Primary hyperparathyroidism

Primary hyperparathyroidism can occur at any age, but children rarely get sick. Hereditary forms of the disease, as a rule, are manifested in children, youth and young age.

[1], [2], [3], [4], [5], [6], [7]

Epidemiology

The notion of the prevalence of the disease radically changed in the early 1970s, when in the United States, and later in Western Europe, automatic biochemical blood analyzers were introduced into general medical practice, and the mandatory components of a regular laboratory examination of all outpatient and hospitalized patients The level of total blood calcium was also included in the healthcare system of these countries. Such an innovative laboratory-diagnostic approach led to the unexpected identification of a huge number of seemingly "asymptomatic" patients with primary hyperparathyroidism who were unlikely to be diagnosed in the usual clinical way. The incidence has increased five-fold in a few years, and the idea of a disease, traditionally accompanied by severe destructive changes in the bones, kidney stones, mental and gastrointestinal complications, has changed dramatically. It became clear that the disease has a long period of latent, low-symptomal course, and in the structure of pathology, erased subclinical forms predominate.

Annually tens of thousands (in the USA - 100 000) of new patients with hyperparathyroidism began to appear in the developed countries of the world, most of whom underwent surgical treatment.

Such high morbidity was explained by the effect of "seizure" of previously previously accumulating malosymptomatic cases of the disease in the population. By the 1990s, the incidence rates began to decline, but in countries where the blood calcium screening system was introduced later, the situation with an epidemic increase in incidence was repeated (for example, in Beijing, China). The current incidence rate, as measured by a large-scale epidemiological study in Rochester, Minnesota, USA, shows a decrease in the incidence rate from 75 to 21 cases per 100 000 population, due to the "washout" of previously accumulated cases of the disease.

However, a recent accurate study of the incidence of primary hyperparathyroidism among women aged 55-75 years in Europe revealed a still high incidence rate of 21 per 1000, which, in terms of the total population, is 3 cases per 1000 population.

No less interesting are the data of autopsy studies of the parathyroid glands in people who died from various causes. The frequency of morphological changes corresponding to different forms of hyperparathyroidism is 5-10% of all autopsies.

Several factors that can affect the change in the incidence of primary hyperparathyroidism are discussed. Among them, an unexpectedly high level of people, especially the elderly, with a vitamin D deficiency (even in Southern Europe), which alleviates hypercalcemia (increases the number of so-called normocalcemic cases of primary hyperparathyroidism), but leads to more severe clinical manifestations of the disease.

Other reasons include the possible impact of ionizing radiation, which can cause a jump in morbidity after 30-40 years of latent period (for example, in connection with man-made accidents, including the consequences of the Chernobyl disaster, nuclear weapons testing, medical radiation in childhood) .

Social factors include an undeveloped system of laboratory screening for hypercalcaemia in countries with inefficient economies and a backward health system, as well as reducing health care costs in developed countries. Thus, in Western Europe, a gradual shift away from total biochemical screening of calcium in the blood is observed, and it is investigated with suspicions of metabolic disorders. On the other hand, increasing attention is paid to screening osteoporosis in older people, which inevitably leads to the identification of a large number of new patients in this common risk group.

An interesting confirmation of the fact that the true incidence rate varies little over time is the recent work of South Korean scientists who identified parathyroid adenoma as a random finding (parathyroid incident) in 0.4% of 6469 patients examined by means of siography and puncture biopsy in communication with the presence of nodes in the thyroid gland.

Thus, Ukraine, where the detection of primary hyperparathyroidism still does not exceed 150-200 cases per year for 46 million people, faces the need to radically change attitudes towards the problem, to introduce a large-scale screening of cases of hypercalcemia, to raise the level of knowledge of physicians of all branches of medicine about primary hyperparathyroidism .

[8], [9], [10], [11], [12], [13],

Causes of the primary hyperparathyroidism

The source of increased synthesis and secretion of parathyroid hormone in primary hyperparathyroidism is one or more pathologically altered  parathyroid glands . In 80% of cases, this pathology is a single sporadically developed benign tumor - adenoma of the parathyroid gland. Hyperplasia of the parathyroid glands, covering, as a rule, all glands (however, not always simultaneously) occurs in 15-20% of cases. In 3-10% of cases (according to different clinical series), the cause of primary hyperparathyroidism can be multiple adenomas (99% double), which, along with hyperplasia of the parathyroid glands, form a group of the so-called multigloydular form of the disease. Many authors now question such a high frequency or even the probability of the occurrence of multiple adenomas of the parathyroid glands, arguing that it is almost impossible to reliably distinguish adenoma from hyperplasia.

Even the use of genetic markers, the principle of monoclonal adenomas, a complex of differential macroscopic and histological criteria does not allow us to distinguish between adenoma and hyperplasia if the site of the normal, unchanged parathyroid gland is not present at the same time in the preparation. In most cases, multi-glandular lesions of the parathyroid glands are hereditary family pathologies that fit into one of the known genetic syndromes or do not have a clear syndrome base.

Rarely (<1% or 2-5% in the clinical diagnosis of the disease, as it predominantly occurs in countries where hypercalcemia is not screened), parathyroid cancer is the cause of hyperparathyroidism.

The pathomorphological classification of tumors and tumor-like formations of the parathyroid glands is based on the International Histological Classification of Endocrine Tumors recommended by the World Health Organization and identifies the following pathology variants of these glands:

1. Adenoma:
   • adenoma from the main cells (central adenoma);
   • oncocytoma;
   • adenoma with vacuolated cells;
   • lipoadenoma.
2. Atypical adenoma.
3. Carcinoma (cancer) of the parathyroid gland.
4. Tumor-like lesions:
   • primary central cell hyperplasia;
   • primary hyperplasia of vacuolated cells;
   • hyperplasia associated with tertiary hyperparathyroidism.
5. Cysts.
6. Parathyreiasis.
7. Secondary tumors.
8. Unclassified tumors.

Typical variants of the pathomorphological picture of lesions of the parathyroid glands with primary hyperparathyroidism are presented in Figures 6.1-6.6 with a brief description of the histological structure.

A rare cause of primary hyperparathyroidism is the parathyroid gland cyst. As a rule, clinically and laboratoryally, such a pathology corresponds to asymptomatic or mild hyperparathyroidism, sonography shows an anechoic formation adjacent to the thyroid gland. When performing differential-diagnostic puncture biopsy, the doctor should be alerted to an absolutely clear (water-clear-water) aspiration fluid, which is not the case with puncture of thyroid nodes, where the cystic fluid has a yellowish-brownish, bloody or colloidal character. The analysis of aspirate on the content of parathyroid hormone, which in case of parathyroid cysts will be greatly increased even in comparison with the patient's blood, can help in the diagnosis.

Excess, parathyroid hormone secretion, which is at the basis of primary hyperparathyroidism, is inadequate to the level of extracellular calcium, is caused either by a decrease in the sensitivity of parathyroid cells to the normal level of calcium in the blood, or by an absolute increase in the mass and quantity of secreting cells. The second mechanism is more characteristic for hyperplasia of the parathyroid glands, the first is much more universal and explains the hyperproduction of parathyroid hormone by both adenomas and some cases of glandular hyperplasia. This discovery was made a little over a decade ago, when Kifor and co-authors in 1996 showed that the specific G-protein of the parathyroid cell membrane bound to the calcium-sensitive receptor is expressed in 2 times less in adenoma cells than in the normal parathyroid gland. This, in turn, leads to a much higher concentration of extracellular Ca ++, necessary to inhibit the production of parathyroid hormone. The reasons for this anomaly are mainly genetic.

However, despite the obvious success of medical genetics, the etiology of most cases of primary hyperparathyroidism remains unknown. There are several groups of genetic disorders that lead to primary hyperparathyroidism or are closely related to its development.

The genetic bases of hereditary syndromic variants of primary hyperparathyroidism have been studied most: the syndromes of multiple endocrine neoplasia - MEN 1 (MEN 1) or MEN 2a (MEN 2a), hyperparathyroidism-jaw tumor syndrome (HPT-JT).

Genetic conditionality has family isolated hyperparathyroidism (FIHPT), as well as a special form of isolated family hyperparathyroidism - autosomal dominant mild hyperparathyroidism or familial hypercalcaemia with hypercalciuria (ADMH).

Family hypocalciuric hypercalcemia (FHH) and severe neonatal hyperparathyroidism (NSHPT) also belong to the category of hereditary syndromes associated with the mutation of the gene encoding the calcium sensory receptor (CASR) in the 3rd chromosome. In the homozygous state of the patient, severe neonatal hyperparathyroidism occurs leading to death from hypercalcemia in the first weeks of life unless an emergency total parathyroidectomy is undertaken. The heterozygous condition is manifested by familial benign hypocalciuric hypercalcemia, which must be differentiated from primary hyperparathyroidism. It, as a rule, does not pose a danger to life and has little effect on the patients' well-being. Operation with this variant of hereditary disease is not shown.

The MEN 1 syndrome, known as Vermeer's syndrome, is genetically mediated by the hereditary tumor lesion of several endocrine organs (primarily the parathyroid glands, pituitary gland, endocrine pancreatic cells), which is caused by the inactivating mutation of the MEN1 gene. This gene is located on the llql3 chromosome, contains 10 epsons and encodes a protein called menin, which is a suppressor of tumors of neuro-ectodermal origin. At the same time, a significant role of a similar mutation in somatic cells was demonstrated in the occurrence of sporadic (non-hereditary) cases of endocrine neoplasias (21% adenoma of the parathyroid glands, 33% gastrin, 17% insulin, 36% bronchial carcinoids), which may indicate a sufficiently high universality of this genetic mechanism.

The syndrome MEN 2a, also called Sipple syndrome, involves the thyroid gland (medullary cancer from C-cells), adrenal medulla (pheochromocytoma) and parathyroid glands (mainly hyperplasia or adenoma 1-2 glands) into the tumor process. The syndrome is caused by an activating embryonic Ret mutation of the proto-oncogene in the 10th chromosome.

The germline mutation of the HRPT2 gene located on the chromosomal arm of lq is responsible for the HPT-JT syndrome, whereas familial isolated hyperparathyroidism (FIHPT) is a genetically heterogeneous disease.

For a number of adenomas of the parathyroid glands, the over synthesis of the regulator of cell division - cyclin D1 (cyclin D1) - is the cause of their development. The pathology is based on clonal chromosomal inversion, in which the 6'-regulatory region of the parathyroid hormone gene (normally located in the chromosomal position of lip 15) moves to the place of the coding region of the oncogene of parathyroid adenoma 1 (PRAD1 / cyclin D1) located at position llql3. This rearrangement causes overexpression of the gene and cyclin D1, responsible for cell cycle disorders and the development of parathyroid adenomas, as well as some other tumors. Excess expression of PRAD1 oncogene is found in 18-39% of parathyroid adenomas.

For more than a quarter of all adenomas of the parathyroid glands, a characteristic cause is the loss of certain tumor suppressor genes, associated with loss of heterozygosity on the chromosomal shoulders lp, 6q, lip, llq and 15q, however, only well-known p53-suppressor tumor for few parathyroid carcinomas.

For parathyroid cancer, a characteristic, but not 100% genetic sign is the deletion or inactivation of the retinoblastoma gene (RB gene), which is now recognized as an important differential and prognostic criterion for diagnosis. Also, a high risk of developing parathyroid carcinoma - 15% - is noted with the syndrome "hyperparathyroidism of the lower jaw" (HPT-JT).

The hypothesis that the main reason for the development of parathyroid adenomas is the mutation of the calcium receptor gene (CASR gene) remains controversial, since it is confirmed by less than 10% of tumors. At the same time, mutations affecting mainly the caudal, cytoplasmic part of this receptor protein are responsible for ADMH, FHH and NSHPT syndromes, the latter of which is most severe and becomes lethal for newborns.

The polymorphism or mutations of the gene-receptor of vitamin D (VDR-gene) are of significant importance in the etiology of primary hyperparathyroidism. Anomalies of vitamin D receptor concentrations are found in adenomas compared to normal parathyroiditis tissue. In 60% of postmenopausal women with primary hyperparathyroidism, gene expression is weakened compared to control.

None of the genetic markers of hyperparathyroidism is able to help distinguish adenoma from parathyroid hyperplasia, as similar genetic changes are found in both the first and second versions of the disease.

In addition, there was not a sufficiently clear correlation between the mass of adenoma and the severity of hyperparathyroidism.

A definite value in the etiology of primary hyperparathyroidism is ionizing radiation. This was first noted in the study of radiation-induced thyroid cancer in individuals receiving therapeutic radiation in childhood. The latent period exceeds that in comparison with thyroid cancer and is 20-45 years. At least 15-20% of patients with primary hyperparathyroidism have an anamnesis of previous exposure. Analysis of a large number of such patients (2,555 people) with a long follow-up period (36 years) made it possible to establish a dose-dependent relationship with radiation, with a significant increase in the relative risk of the disease (from 0.11 cGy) and no effect of sex or age at the time of the disease.

[14], [15], [16], [17], [18], [19], [20], [21], [22]

Symptoms of the primary hyperparathyroidism

During the first decade of conscious study of clinical cases of primary hyperparathyroidism, almost all patients had fibrocystic osteitis, which was considered to be the main and perhaps the only specific manifestation of the disease. As already indicated in the historical essay on primary hyperparathyroidism, at the beginning of the 20th century, researchers believed that the destruction of bones is primary and only then leads to secondary compensatory hyperplasia of the parathyroid glands. Only in 1934 F. Albright noted that 80% of patients with fibrocystic osteitis have renal damage in the form of urolithiasis or nephrocalcinosis. With the presentation of this authoritative scientist, in the next 20-30 years, urolithiasis became the defining symptom of primary hyperparathyroidism. Later, in 1946, the relationship between primary hyperparathyroidism and peptic ulcers of the stomach and duodenum was traced. A frequent combination of the disease with gout (due to an increase in the concentration of uric acid in the blood) and pseudogout (due to the deposition of calcium phosphate crystals) was also found.

In 1957, summarizing the known clinical symptoms of primary hyperparathyroidism, WS Goer was the first to propose a capacious mnemonic characterization of the manifestations of the disease in the form of a triad of "stones, bones, and abdominal groans" (later bones, stones, abdominal complaints), later supplemented with one more component - mental disorders, that the original received a rhyming sound: "stones, bones, abdominal groans and psychical moans".

Symptoms of primary hyperparathyroidism today rarely fit into such a scheme. The worn-out clinical forms predominate, although urolithiasis continues to occur in approximately 30-50% of patients. Quite often (about 5-10% of cases) as a concomitant disease there is gallstone disease. So, according to the American authors, in 1981 of 197 examined patients with primary hyperparathyroidism in 51% of cases there was urolithiasis and in 24% - X-ray signs of bone damage. In the late 90s of the last century, only 20% had nephrolithiasis, bone involvement became very rare.

Even in countries where the screening of hypercalcemia and primary hyperparathyroidism is low (including in Ukraine), patients are less likely to display vivid symptoms with severe damage to the bones of the skeleton, urolithiasis, gastrointestinal manifestations, neuromuscular and psychiatric disorders.

A sharp increase in the frequency of detection of the disease with the onset of widespread use of biochemical blood tests on automatic analyzers in developed countries led to a "washout" of clinically pronounced cases of primary hyperparathyroidism, which in turn changed the structure of the new patients' clinic to a large predominance of asymptomatic or low-symptom forms 10-20% before the introduction of hypercalcemia screening to 80-95% of such patients in the last two decades). In this regard, interest in describing the clinical picture of the disease in the modern literature has significantly weakened. Large-scale monographs on primary hyperparathyroidism, and those only casually concern the issue of clinical symptoms. The emphasis in them is on the need not selective (with suspicion of disease), but a continuous survey of the population by periodically determining the level of calcium in the blood.

At the same time, it can be assumed that in the context of limited funding for medical projects in developing countries, clinically-oriented approaches to the diagnosis of primary hyperparathyroidism will still be relevant for a long time. Therefore, knowledge of possible manifestations of the disease will undoubtedly benefit both from the point of view of diagnosis and differential diagnosis, and from the point of view of predicting the development of certain pathological conditions associated with primary hyperparathyroidism.

Directly related to the pathological effect of excess parathyroid hormone are only changes in the bone system - systemic osteoporosis and subperiosteal resorption of long bones, which are accompanied by a decrease in the strength of the skeleton, increased propensity to fracture, pain in the bones. The effect of parathyroid hormone on the renal tubules can lead to a decrease in renal function even in the absence of urolithiasis. The possibility of direct action of parathyroid hormone on the muscle of the heart, which causes hypertension, left ventricular hypertrophy and insufficiency is also discussed. Both recent syndromes (renal and cardiac) are now being closely studied in the context of reversibility of these changes after the cure of hyperparathyroidism, but controlled randomized studies have not yet been conducted.

The remaining symptoms are predominantly mediated (via hypercalcemia) origin. These include the formation of calcium deposits (calcification of parenchymal organs, vessels, cornea, soft tissues) and kidney stones, bile and pancreatic ducts, the effect of increased concentrations of extracellular calcium on neuromuscular conduction, muscle contractility, secretion of digestive glands and many other physiological processes (see sections "Physiology of calcium metabolism", "Etiology and pathogenesis of primary hyperparathyroidism").

Symptoms and complaints that can occur in patients with primary hyperparathyroidism

Urinary

• Polyuria, back pain, renal colic, hematuria

Musculoskeletal

• Pain in the bones, especially in the long tubular, joint pain, swelling, tendency to fracture, pathological bone fractures (ray, hip, clavicle, humerus, etc.)

Digestive

• Anorexia, nausea (in severe cases - vomiting), dyspepsia, constipation, abdominal pain

Psychoneurological

• Depression, weakness, fatigue, apathy, lethargy, confusion of different degrees of severity, psychosis

Cardiovascular

• Arterial hypertension, bradycardia, arrhythmia

Many of the patients now can not make specific complaints, even with the targeted questioning. Some of the patients assess their condition only retrospectively, after the successful surgical treatment of primary hyperparathyroidism, noting that they have acquired a "new, better quality of life" consisting of many components: greater vitality, higher physical performance, a positive attitude toward life, better memory, the disappearance of joint stiffness and muscle weakness, etc. Illustrative are works based on the principles of evidence-based medicine, which used subtle tools to assess the psychological and emotional state of patients (the most popular questionnaire of psychosocial well-being is SF-36 and a detailed scale of assessment of psychosomatic symptoms - SCL-90R.

They convincingly showed that after surgical treatment of primary hyperparathyroidism for a certain time (from 6 months to 2 years) significant positive changes in the quality of life, a reduction in pain, a rise in vitality and other positive changes that the patient rarely describes independently can occur. In the same control groups of patients who were under observation, such changes did not occur.

The work, which investigated the dynamics of the condition of patients who did not receive treatment, noted the gradual progression of complaints or their appearance during 10 years of follow-up. One of the studies recorded clear indications for surgical treatment in 26% of patients and death from various causes in 24%. In another long prospective study of the course of mild forms of hyperparathyroidism, progression of the disease in 24%, the appearance of new concrements in the urinary tract, hypercalcemia crises, the need for emergency parathyroidectomy was established. A large number of works demonstrate a steady progression of reducing bone mineral density with an increase in the duration of the disease, regardless of the initial condition, sex and age.

The accumulation of such data led to an understanding of the need to develop consensus on indications for surgical treatment of asymptomatic clinical forms of primary hyperparathyroidism. Such consensus under the auspices of the National Institutes of Health of the United States (NIH) has been accepted and amended three times since 1991 (the latest revision in 2009). The essence of these recommendations is reduced to attempts to objectify the indications for surgery with erased forms of the disease, based on such criteria as the severity of hypercalcemia, severity of osteoporosis, renal dysfunction, the presence of urolithiasis, the age of patients (less than or more than 50 years) and their adherence to a thorough medical observation. This will be discussed in the section on the surgical treatment of primary hyperparathyroidism. In addition, a thorough study of the patient's psychoneurological condition shows the presence of such "small" symptoms in almost all patients, which makes the concept of the asymptomatic variant of the disease not entirely legitimate.

Renal manifestations of the disease remain one of the most recurring clinical symptoms, although their severity and frequency decrease. It is unclear why the renal concrements are not formed in a number of patients with a long history of hyperparathyroidism, as well as the lack of correlation between the severity of hyperaratyroidism, the severity of hypercalciuria, and the presence of urolithiasis. The formation of kidney stones is facilitated by tubular acidosis, which arises from increased excretion of bicarbonate under the influence of parathyroid hormone. In addition to anatomical changes in the kidneys (stone formation, nephrocalcinosis, secondary-wrinkled kidney due to chronic pyelonephritis against the background of a long-term urolithiasis), the primary hyperparathyroidism is also characterized by functional changes that develop with the progression of hyperparathyroidism, resulting in chronic renal failure and associated mainly with a lesion of the proximal renal tubules. Typical manifestations of functional renal impairment are proximal tubular acidosis of the second type, amino- and glucosuria, polyuria.

The effect of bone parathyroid hormone, previously considered the only manifestation of primary hyperparathyroidism, is capable of demonstrating destructive effects in patients with very severe and prolonged primary hyperparathyroidism, although it is increasingly rare in the form of the classical form of fibrocystic osteitis. According to foreign authors, if in the 30s of the XIX century the frequency of this syndrome exceeded 80%, by the 50th years it decreased to 50%, to 70% to 9%, and in the era of calcium screening - almost to zero. It is extremely rare to see a detailed X-ray picture of bone lesions - subperiosteal resorption, cyst formation, hypertrophy of the periosteum, pathological fractures, diffuse demineralization ("transparent" bones), uneven resorption and rearrangement of bone substance in the bones of the skull, manifested by the X-ray symptom "salt and pepper" .

The effect of parathyroid hormone is dual, as it was established in the 90s of the last century, and depends not only on the absolute amount of the secreted hormone, but also on the nature of the secretion - constant or pulsating. The maximum osteorheptive effect is observed in bones with a pronounced cortical structure (long tubular bones), whereas the bones of the trabecular structure (vertebrae, iliac crest) can retain their density or even increase it. This effect has a certain differential diagnostic value when, in the X-ray absorption densitometry of patients with primary hyperparathyroidism, bone density in the radius of the radius is recorded, less in the femoral bone and is often absent in the vertebrae. In the typical case of postmenopausal hypoestrogenic osteoporosis in women older than 50 years, a decrease in density is observed primarily in the vertebrae.

At the same time, the fact of increasing the mineral density in the first place, namely sponge bones (vertebral bodies and proximal thigh), and to a lesser degree of radius after surgical treatment of patients with primary hyperparathyroidism, remains inconclusive. This fact was confirmed by independent studies of different years that evaluated the comparative dynamics of bone density in groups of patients with moderate hyperparathyroidism who underwent surgery or who received conservative treatment (bisphosphonates, calcium mimetics) or who were under observation. It is believed that the restoration of the normal (pulsating) type of parathyroid hormone secretion is a more powerful stimulus for restoring the density of spongy bones than the absolute decrease in the concentration of the hormone. The defeat of the compact substance of the tubular bones remains almost irreversible even after the elimination of hyperparathyroidism.

In the process of observation and even treatment with calcium mimetics (zincalcet), a significant increase in the mineral density of bones was not achieved. Tsinakalcet, although it led to a decrease in the level of calcium in the blood, but practically did not affect the level of parathyroid hormone.

Thus, long-term primary hyperparathyroidism is fraught with catastrophic consequences for the skeleton, regardless of the type of bone structure. In addition to the risk of pathological fractures of long bones, flattening of vertebral bodies, kyphoscoliosis, and a sharp decrease in human growth are observed.

A rare but very specific radiologic symptom is the formation of "brown" or "brown" tumors (in the foreign literature - brown tumors), more often in spongy bones - jaws, collarbones. These pseudotumoral formations of the granulomatous structure simulate the bone neoplastic process, causing tragic diagnostic and medical errors. So because of a false diagnosis of sarcomas, bones perform amputations, make crippling operations on the jaws, whereas similar changes in hyperparathyroidism are reversible and require only the elimination of the cause of primary hyperparathyroidism.

It should be remembered the possible combination of such jaw tumors and primary hyperparathyroidism within the hereditary syndrome of the same name (JT-PHPT syndrome), in which there is a high probability of a malignant tumor of the parathyroid gland (up to 20%), which requires correction of therapeutic tactics.

Joints are also a weak link in the body of patients with primary hyperparathyroidism. The load on them increases due to erosive changes in the epiphyses, the violation of the geometry of the bones. Another pathogenetic factor of arthropathy is the deposition of calcium salts in synovial membranes, cartilage and periarticular, which leads to chronic trauma and severe pain syndrome.

Neuromuscular changes in primary hyperparathyroidism are manifested in weakness and fatigue, mainly affecting the proximal muscles of the lower limbs. This reversible syndrome, rapidly disappearing after surgery, characterized in vivid cases by a typical complaint - difficulty getting out of the chair without help.

Psychoneurological disorders can sometimes be very difficult to assess because of the personal or age characteristics of patients. In general, they respond to the symptoms of depressive conditions, personality changes, memory impairment. Sometimes, especially with significant hypercalcemia, there may be obvious psychotic states or confusion, inhibition, lethargy right up to coma. To identify personal changes helps to communicate with relatives or close people to the patient. Some patients, because of the lack of timely diagnosis of hyperparathyroidism, become dependent on antidepressants, analgesics, neuroleptics of other psychotropic substances.

Gastrointestinal symptoms may include a clinic of  peptic ulcer of the stomach  or duodenum, hyperacid gastritis, cholelithiasis, chronic, and sometimes acute pancreatitis. Disturbances of the digestive system can be both true manifestations of hyperparathyroidism and hypercalcemia, and the consequences of concomitant hypergastrinemia within the framework of MEN-1 syndrome or Zollinger-Ellison syndrome.

The causal relationship between hyperparathyroidism and pancreatitis, which is observed in 10-25% of patients, is not completely understandable. Probable causes are called gastric juice hyperacidity and camp formation in the ducts. Not only hypercalcemia, but also normocalcemia in acute pancreatitis should alert clinicians, since free fatty acids due to excessive lipolysis bind calcium, leading to a decrease in its concentration in the blood.

Arterial hypertension is much more common in patients with primary hyperparathyroidism than in the general population, although the exact mechanisms for this effect remain poorly understood. Among the possible causes are the direct action of parathyroid hormone on the heart muscle, left ventricular hypertrophy, calcification of heart valves, myocardium and aorta (more than half of patients). By itself, parathyroidectomy does not always significantly affect the further course of hypertension, although left ventricular hypertrophy turns out to be reversible in most patients.

Bradycardia, unpleasant sensations in the heart, interruptions in his work are often found in primary hyperparathyroidism and correlate with the severity of hypercalcemia.

Primary hyperparathyroidism, in addition to gradually developing pathological changes in many organs and tissues, can also cause urgent life-threatening conditions, the main of which is the hypercalcemic crisis. The severity of clinical manifestations as a whole correlates well with the severity of hypercalcemia, but there are cases with a relatively mild course of the disease with calcicemia exceeding 4 mmol / l and cases with a severe clinical picture of severe hypercalcemia with a calcium level of 3.2-3.5 mmol / l. This depends on the rate of increase in the concentration of calcium in the blood and the presence of intercurrent diseases.

Expressed hypercalcemia (usually more than 3.5 mmol / l) leads to anorexia, nausea, vomiting, which further exacerbates the increase in calcium concentration. Weakness and lethargy associated with the central and neuromuscular action of abnormally high levels of calcium lead to immobilization of the patient, which enhances the osteorheptive processes. Gradually pathological brain disorders are aggravated, confusion occurs and in the future - coma (the level of calcium usually exceeds 4.3-4.4 mmol / l). If the patient is not in such a condition, then the oliguric renal failure, heart rhythm disturbance and death develop.

In general, even moderate severity of primary hyperparathyroidism significantly increases the risk of premature death, mainly from cardiovascular and circulatory complications, the consequences of bone fractures, peptic ulcers and, according to some reports, more frequent oncological diseases. Recent population studies of Scottish scientists on a vast array of data (more than 3,000 cases of disease) showed a twofold increase in the risk of developing malignant tumors and a threefold increase in the risk of death for patients with primary hyperparathyroidism compared with the corresponding cohorts of people without hyperparathyroidism.

It is characteristic that for patients who were operated in the pre-erasing era (ie, predominantly with a long history and a vivid clinical picture), the risk of premature death remains elevated for 15 years or more after the operation. At the same time, patients diagnosed in the early stages of the disease, with a short history, gradually equalize the risk of premature death with population control groups. Danish scientists confirmed such data, establishing increased risks of diseases and death from cardiovascular diseases, bone diseases and peptic ulcers of the stomach, these risks decreased after surgical treatment, although they did not reach the level of control groups. It was possible to calculate even the mathematical dependence of the expected risk of death on sex, age and weight of the tumor of the parathyroid gland.

Thus, primary hyperparathyroidism is a chronic disease with a multifaceted clinical picture (now far from classical descriptions of the disease) involving many organs and systems in the pathological process, leading to a significant quality of life deficit, an increased risk of premature death and the risk of malignant tumors. Early diagnosis and timely surgical treatment can significantly reduce or eliminate the above risks, significantly improve the quality of life of patients.

Diagnostics of the primary hyperparathyroidism

Laboratory diagnosis of primary hyperparathyroidism is the basis for timely recognition of primary hyperparathyroidism and the widest possible detection of the disease in the population.

The key criteria for the laboratory diagnosis of primary hyperparathyroidism are two indicators: elevated levels of parathyroid hormone and elevated levels of calcium in the blood plasma. Simultaneous detection in the patient of these two laboratory signs leaves little doubt in the diagnosis of primary hyperparathyroidism. Thus, with classical bright variants of the course of the disease, its laboratory diagnostics can not but amaze with its simplicity. Why then are mistakes made so often in the diagnosis? Why does the unrecognized disease continue to develop for decades, leaving devastating traces in the body? ..

Further, we will try to analyze possible pitfalls in the laboratory diagnosis of primary hyperparathyroidism, the causes of errors, the ways of verification of the diagnosis, as well as pathological conditions that mask or simulate the biochemical picture of the disease.

Let's start with the main indicators: calcium and blood parathyroid hormone.

Calcium in the blood learned to determine in the clinic a little over a hundred years ago - in 1907. In blood, calcium is in three main forms: the ionized fraction of the element is 50%, the fraction associated with proteins is 40-45%, the fraction consisting of complex phosphate and citrate compounds - 5%. The main clinical laboratory parameters of studying this element in the body are the concentration of total calcium and the concentration of ionized (or free) calcium of blood.

The range of normal values of total calcium is 2.1-2.55 mmol / l; ionized calcium - 1.05-1.30 mmol / l.

It should be noted that the upper limit of the normal values of total calcium has been reviewed repeatedly over the past 30 years, each time with a downward correction and decreased from 2.75 to 2.65 and 2.55 mmol / l in the latest guidelines. Total calcium is the most widely used indicator, which is used as one of the main components of complex biochemical blood tests using modern automatic analyzers. It was the introduction of an automatic study of total calcium that helped to discover the true frequency of primary hyperparathyroidism in the population.

With this research technique, this parameter is sufficiently reliable, since it depends little on the human factor, while observing the standard requirements for fencing and determination. However, in real practice of domestic medicine, it is possible to meet more often with a manual biochemical study of blood for total calcium, in which quite gross deviations are possible both in the direction of diminution (prolonged blood stay in a test tube at room temperature, calibration errors, etc.). And in the direction of increase (glassware, not plastic vacuumers for blood sampling and centrifugation, impurities of other reagents, etc.).

In addition, even a correctly performed analysis of the determination of total blood calcium requires adjustments in blood levels of proteins, especially albumin. The lower the albumin concentration compared to the norm (40 g / l), the higher the true calcium concentration should be when compared with the recorded concentration, and conversely, when the albumin concentration increases, the correction should be made towards decreasing the level of calcium in the blood. The method is rather approximate and requires an adjustment of 0.2 mmol / L for every 10 g / L deviation from the average albumin value.

For example, if the laboratory concentration of total calcium is 2.5 mmol / l, the albumin level is 20 g / l, then the adjusted calcium concentration is 2.9 mmol / l, i.е. 2.5 + (40-20): 10 PROGRESS

Another method of correcting the indicator of total calcium by blood protein level implies correction of the total calcium value depending on the concentration of the total protein of the blood.

Thus, it is realistic not to miss the true hypercalcemia with a reduced level of albumin or a common protein of the blood. The reverse picture can be observed with an increase in the concentration of plasma proteins, which happens, for example, in myeloma. A sharp increase in the protein-bound fraction of calcium will lead to an elevated level of total calcium in the blood. Such errors can be avoided by directly determining the ionized blood calcium. This indicator is less variable, but for its determination requires special equipment - an analyzer using ion-selective electrodes.

The correctness of the definition and interpretation of the indicator of the level of ionized calcium depends on the technical condition and careful calibration of the equipment, as well as on the influence of the blood pH level on the calcium concentration. The acid-base state affects the content of ionized calcium in the blood by affecting the process of binding calcium to proteins. Acidosis reduces the binding of calcium to blood proteins and leads to an increase in the level of ionized calcium, while alkalosis increases the process of calcium binding to proteins and reduces the level of ionized calcium. This correction is incorporated in the automatic program of modern ionized calcium ion analyzers, but was not used in earlier models, which may lead to an incorrect evaluation of the indicator and be one of the reasons for the delay in establishing the correct diagnosis of primary hyperparathyroidism.

The main external factors affecting the level of calcium blood are the intake of vitamin D and thiazide diuretics (both factors contribute to its increase). More details on the regulation of calcium metabolism and the causes of hypercalcemia are mentioned in the relevant sections of the monograph.

The second of the main components of laboratory diagnosis of primary hyperparathyroidism - the level of parathyroid blood hormone - also requires a competent evaluation and consideration of objective and subjective factors capable of distorting its true meaning.

We will not consider the features of the previously used laboratory tests for fragments of the parathyroid hormone (C- and N-terminal parts of the molecule). They had a number of limitations and inaccuracies, so now they are practically not used, giving way to immunoradiometric or enzyme immunoassay of an entire (intact) parathyroid hormone molecule consisting of 84 amino acid residues.

The normal range of parathyroid hormone concentrations in healthy subjects is 10-65 μg / L (pg / ml) or 12-60 pmol / dl.

Possessing undoubted advantages over the terminal fragments of the parathyroid hormone in terms of the adequacy of the parameter to the investigated targets, the determination of intact parathyroid hormone is associated with a number of difficulties. First of all, it is a very short half-life of the molecule in the body (several minutes) and the sensitivity of the analysis to the timing of blood and serum stay at room temperature. That's why sometimes the analyzes made on the same day in different laboratories vary. After all, it is enough to collect blood not in a vacuum, but into an open test tube, leave the tube at room temperature for 10-15 minutes or use an uncooled centrifuge - and the result of the analysis can significantly change in the direction of underestimation of concentration. As a rule, in practice, it is a false underestimation of the results of the study, which is why, from a few serial studies in a short time, you should trust the highest result. Therefore, critically important is not only the standardization of hormonal research itself, but also the stage of blood sampling and preparation of serum for analysis. This should occur with the shortest possible length of blood stay in the uncooled form. In short, the more standardized and automated the process of blood sampling and analysis, the more reliable the results.

In the last decade, reagents of the second and third generation appeared, as well as automatic devices for instant blood testing for parathyroid hormone, used primarily intraoperatively to assess the radical nature of the operation. The latest development of the Dutch firm Phillips, promulgated at the congress of the European Society of Endocrine Surgeons (ESES-2010, Vienna) promises to simplify the procedure to a minimum, automate all processes (the device is loaded not with plasma but with whole blood!) And shorten the study time to 3-5 minutes.

When assessing the results of the study of blood parathormone, it is necessary to take into account the daily rhythm of hormone secretion (with peak concentration at 2 am and minimum at 2 pm), the possibility of interference in the night mode of operation.

Some medicines may alter the natural concentration of parathyroid hormone. So, phosphates, anticonvulsants, steroids, isoniazid, lithium, rifampicin increase the concentration, and cimetidine and propranolol reduce the level of parathyroid hormone in the blood.

Apparently, the most significant effect on the correct assessment of the main laboratory pair of criteria - calcium / parathyroid hormone - is a decrease in kidney function and vitamin D deficiency, the frequency of which is largely underestimated by physicians.

Violation of renal function has a multifaceted impact on both primary diagnosis and clinical evaluation of the course of primary hyperparathyroidism. Thus, a decrease in creatinine clearance by 30%, and in the latest edition of the manual on asymptomatic primary hyperparathyroidism, a decrease in glomerular filtration below 60 ml / min is recognized as an indication for surgical treatment of low-symptom variants of the disease. However, a prolonged impairment of renal function, which could be caused by direct action of the parathyroid hormone or secondary pyelonephritis on the background of urolithiasis, is itself accompanied by an increased loss of calcium in the urine (primarily in response to reduced phosphate excretion due to a loss of ability to remove it from the affected kidneys ). The early appearance of a deficiency of active 1,25 (OH) 2-vitamin D3 in renal failure (due to a decrease in renal la-hydroxylase activity) also contributes to a certain decrease in serum calcium concentration due to reduced absorption in the intestine. These factors are largely able to explain the frequent cases of normocalcemic primary hyperparathyroidism or the lack of stable hypercalcemia, which makes it difficult to diagnose.

Normocalcemic primary hyperparathyroidism, according to authoritative modern scientists, is a real diagnostic problem and a challenge to modern laboratory diagnostics; it must be differentiated from cases of idiopathic hypercalciuria associated with increased calcium absorption in the intestine, reduced tubular reabsorption of calcium, or primary hyperphosphaturia in order to avoid unnecessary operations. On the other hand, untimely diagnosis of primary normocalcemic hyperparathyroidism will lead to an increase in renal failure, the formation of new urinary stones.

A test with thiazide diuretics can help distinguish between these two conditions, which are close in laboratory terms. The appointment of the latter will lead to correction of hypercalciuria associated with "dumping" excess calcium and normalizing the level of parathyroid hormone. With normocalcemic primary hyperparathyroidism, thiazide diuretics will promote hypercalcemia and will not reduce the level of parathyroid hormone.

In connection with the above circumstances, it is necessary to mention another very important criterion of laboratory diagnostics - the level of daily calciuria. This indicator is more differential than diagnostic value. It allows you to differentiate similar to the main criteria (simultaneous increase in the level of calcium and parathyroid hormone in the blood) disease - family benign hypocalciuric hypercalcemia. This pathology has now become more understandable and represents more than one, but a whole group of conditions associated with a violation of the regulation of calcium metabolism, which is based on mutations in the gene of the calcium receptor (they are known for more than 30). A major difference in this condition, in which stable hypercalcemia and a slight increase in the level of parathyroid hormone will be observed, is a decrease in the level of calciuria (usually less than 2 mmol / day), whereas in primary hyperparathyroidism, the calcium level remains normal or increases (more than 6-8 mmol / l) , depending on the severity of the process and the state of kidney function.

The most accurate method of assessing calciuria is to calculate the calcium clearance ratio for creatinine clearance, as calcium excretion directly depends on the glomerular filtration rate. The calculation formula is as follows:

Clearance Sa / Clearance Cr = Sau X Crs / Cru x Cas

Where Cau - urine calcium, Cr, - serum creatinine, Cru - urine creatinine, Cas-serum calcium.

It is important that all indicators are converted to the same units of measurement (eg, mmol / L). Differentiation (in favor of familial hypocalciumuric hypercalcemia) is the ratio of 1: 100 (or 0.01), whereas in primary hyperparathyroidism it is usually 3: 100-4: 100. The investigation of blood relatives (siblings of the 1st line) , since the disease is autosomal dominant and probabilistically affects half the offspring (with the development of laboratory manifestations already in early childhood). Due to the low-symptom course of the disease, treatment is generally not required, and the operation does not have a significant clinical effect.

No less difficult is the effect of vitamin D deficiency on clinical manifestations and laboratory diagnosis of primary hyperparathyroidism.

Vitamin D acts as a whole synergistically with parathyroid hormone, exerting a hypercalcemic effect. However, there is also a direct negative interaction of vitamin D with parathyroid cells, inhibiting the synthesis of parathyroid hormone (with excess of vitamin) and stimulating its production (with its lack) through molecular mechanisms of gene transcription and, possibly, by direct action on certain receptors.

Deficiency of vitamin D, previously associated exclusively with pediatric problems, has proved extremely prevalent in all age groups, even in well-developed developed countries. So among hospitalized patients in the US, vitamin D deficiency was detected at a frequency of 57%. The problem is now so urgent that the question of revising the normal limits of the concentration of parathyroid hormone in the blood (with the establishment of an optimum minimum and a safe upper limit), taking into account the degree of vitamin D deficiency, is being debated. Consensus guidance on the diagnosis and treatment of asymptomatic primary hyperparathyroidism calls for determining the level 25 (OH) of vitamin D in all patients with suspected primary hyperparathyroidism.

If a lower (or less than 20 ng / ml) or low-normal 25 (OH) vitamin D level is detected, a careful correction should be made with a subsequent re-examination to decide the treatment strategy. At the same time, many authors focus on changing the clinical course of primary hyperparathyroidism in conditions of vitamin D deficiency (mainly in the direction of weight gain), in spite of less pronounced biochemical shifts. Unfortunately, the determination of vitamin D concentration in Ukraine remains inaccessible due to the high cost of research and its implementation only in commercial laboratories.

Among the primary additional criteria for diagnosis and differentiation of primary hyperparathyroidism and some other conditions with similar clinical and laboratory indicators is the level of phosphorus in the blood. The normal value of phosphatemia for adults is in the range of 0.85-1.45 mmol / l. Primary hyperparathyroidism is characterized by a decrease in this index to the lower limit of the norm or below it with severe hypercalcemia, which occurs in about 30% of patients. This parameter is particularly indicative in the detection of a simultaneous increase in renal excretion of phosphorus, associated with the inhibition of phosphate reabsorption by PTH. Hypophosphatemia can occur in some patients with cholestatic liver disease.

Recall that the levels of calcium and phosphorus in the blood are extremely closely related in an inverse proportion; the index of the product of serum concentrations of total calcium and phosphorus (Ca x P) is a very important and stable parameter of human homeostasis, controlled by many systems. Exceeding this product to values greater than 4.5 (mmol / L) 2 or 70 (mg / L) 2 leads to massive formation in the blood of insoluble calcium phosphate compounds, which can cause all kinds of ischemic and necrotic lesions. In addition to the diagnostic value (to confirm the diagnosis of primary hyperparathyroidism), the level of phosphorus in the blood serves as a differentiating criterion for the disengagement of primary and secondary hyperparathyroidism caused by chronic renal failure.

In this case, the level of phosphorus tends to increase depending on the severity of impaired renal function, which is associated with a loss of ability to actively excrete phosphates. Severe hyperphosphatemia in terminal stages of chronic renal failure can be corrected only by hemodialysis, so it is necessary to evaluate the indicator before dialysis. In addition to hyperphosphatemia, a distinctive feature of secondary hyperparathyroidism will always be a normal or reduced level of calcium in the blood, until the disease goes into the next phase - tertiary hyperparathyroidism (development of adenomas against the background of prolonged hyperplasia of parathyroid glands with autonomization of their function).

An additional laboratory diagnostic criterion is also moderate hyperchloremia. It refers to non-permanent symptoms. A more accurate indicator is the ratio of the concentration of chlorine to phosphorus in the blood - in primary hyperparathyroidism it exceeds 100 when measured in mmol / l, and in the norm - less than 100.

Useful for diagnosing and determining the severity of the disease are the indicators of enhanced bone reshaping and osteorheal resection under the effect of prolonged excessive release of parathyroid hormone into the blood. Among the markers of osteorecorrection include elevated levels of alkaline phosphatase (its bone fraction), osteocalcin of the blood, as well as urinary excretion of hydroxyproline and cyclic adenosine monophosphate. However, these indices are non-specific, can occur in any form of hyperparathyroidism and other conditions associated with active bone reshaping (for example, in Paget's disease). Their values are more informative as indicators of the severity of the lesion of the bone system.

Thus, summarizing the principles of laboratory diagnosis of primary hyperparathyroidism, the following key theses can be formulated.

Screening of hypercalcemia is the most rational method of detecting primary hyperparathyroidism in a population.

The most important diagnostic indicators are the simultaneous increase in calcium and blood parathyroid hormone. In this case, certain proportions of this increase should be taken into account: calcium in primary hyperparathyroidism rarely exceeds the level of 3 mmol / l; severe hypercalcemia, usually accompanied by a very high level of parathyroid hormone (at least 5-10-fold).

Implicit hypercalcemia and a slight increase in the level of parathyroid hormone (or its upper-normal values) are more typical for familial hypocalciuric hypercalcemia. Confirm it can be studied daily calcium (should be reduced), preferably in relation to the clearance of creatinine, as well as a survey of blood relatives.

Moderate increase (or upper-normal values) of blood calcium and a slight increase in the level of parathyroid hormone are more evidence of primary hyperparathyroidism (erased forms) due to the unsuppressed parathyroid hormone level, which normally decreases rapidly due to a mammoth reactive decrease in its secretion by the parathyroid glands in response to a slight increase in blood calcium levels.

All cases of endothelial hyperscalcaemia (malignant tumors, myeloma, granulomatosis, thyrotoxicosis, etc.) or exogenous (hypervitaminosis D, thiazide diuretics, milk-alkaline syndrome, etc.) are accompanied by a suppressed or even zero blood parathyroid hormone level.

Secondary hyperparathyroidism presents a diagnostic problem more often with a primary vitamin D deficiency, when there is a moderate increase in the level of parathyroid hormone and a normal level of calcium in the blood. Secondary hyperparathyroidism of renal genesis is easier to diagnose because of the presence of hyperphosphataemia and a lower or lower normal level of calcium in the blood, as well as signs of impaired renal function.

In any of the clinical variants of the disease, a weighted decision on the final diagnosis, a serial study of the parameters, a study of additional diagnostic factors is very important in connection with the fundamental differences in therapeutic tactics with primary hyperparathyroidism and other conditions.

Among the necessary laboratory tests for primary hyperparathyroidism, genetic testing for the presence of possible mutations determining the development of hereditary forms of hyperparathyroidism (MEN-1, MEN-2a, PHT-JT-syndrome) and variants of the pathology of the gene coding for the calcium receptor should be attributed. However, we still have to state the practical inaccessibility of genetic methods for widespread clinical use in Ukraine.

How is primary hyperparathyroidism diagnosed?

Instrumental research methods for primary hyperparathyroidism are aimed at:

1. confirmation of diagnosis;
2. the establishment of the severity of the course of the disease and the defeat of other organs and systems (bones, kidneys);
3. topical diagnostics and visualization of pathologically altered and hyperfunctioning parathyroid glands.

The truly diagnostic role of instrumental methods of examining patients with suspected primary hyperparathyroidism is low. Detection of certain indirect symptoms will still be of an auxiliary nature and will not be qualified in the diagnosis without the basic laboratory criteria of the disease. At the same time, it should not be forgotten that for a significant part of patients, the impetus to purposeful diagnosis is still the accidental detection of certain clinical, radiologic, sonographic or densitometric signs of the disease. Therefore, in the aggregate of data allowing you to think about the diagnosis, it is certainly worth taking into account the data of ultrasound examination of the abdominal cavity and retroperitoneal space: echo-positive concretions in the kidneys and urinary tracts, concrements of the biliary tract and gallbladder, nephrocalcinosis. Especially should be alarmed by recurrent stones in the kidneys and coral concrements. The frequency of primary hyperparathyroidism among their owners reaches 17%.

Although ultrasound examination of the kidneys is not considered mandatory for primary hyperparathyroidism, however, the presence of urolithiasis, even with minor biochemical changes, will indicate a clinically pronounced disease requiring surgical treatment.

X-ray methods for primary hyperparathyroidism include an overview radiograph of the chest and abdominal cavity (they allow to identify accidentally consolidated fractures of the ribs, calcification of the heart valves, pericardium and aorta, X-ray positive kidney stones, so-called "brown" tumors or granulomatous growths in the spongy bones - crest of the ilium, ribs, vertebrae, establish kyphoscoliotic curvature of the spine, detect foci of metastatic calcification of soft tissues, calcium the fication of tendons, synovial bags, joints), as well as targeted x-ray examination of the bones of the skeleton.

The greatest experience of X-ray semiotics of primary hyperparathyroidism was accumulated at the time of the vast predominance of bone forms of primary hyperparathyroidism, in the pre-scraping era of the first half of the 20th century. Now, when the disease is recognized mainly by the laboratory pathway in the early stages of the development of pathology, the frequency of X-ray signs of hyperparathyroidism has significantly decreased. Moreover, the errors of radiologists that do not notice or misinterpret the marked osteodystrophic changes in the skeleton, which are characteristic of primary hyperparathyroidism, are inadmissible.

In order to reduce the incidence of X-ray changes in bones in primary hyperparathyroidism, there are:

1. diffuse thinning of the cortical bone;
2. osteosclerosis (mainly pelvic bones, skull);
3. osteolysis of nail phalanges of brushes and feet;
4. subperiosteal resorption (in the first place - the radial surfaces of the middle phalanx of the fingers of the hand, the distal part of the ulna);
5. formation of bone cysts in long tubular bones and upper and lower jaws, ribs, collarbone;
6. pathological fractures and traces of their delayed consolidation.

X-ray signs of skeletal lesion in primary hyperparathyroidism (uneven focal resorption and alteration of skull bone substance - "salt and pepper").

One of the characteristic features of severe secondary hyperparathyroidism is massive diffuse and focal deposits of insoluble calcium-phosphate compounds in soft tissues of various locations, which can be clearly seen both in conventional planar radiography and in computed tomography. With primary hyperparathyroidism and preserved kidney function, metastatic calcium deposits are rare because of a simultaneous reduction in the level of phosphorus in the blood with hypercalcemia.

The electrocardiographic changes characteristic of primary hyperparathyroidism and reflecting the predominantly hypercalcemic state of patients, as well as hypertrophy of the myocardium, also have definite diagnostic value. Such changes in the ECG curve include shortening of the QT interval, prolongation of the PR interval, expansion of the QRS complex, shortening of the ST interval, flattening or inversion of the T wave, its extension.

The results of densitometric studies of bones are of great diagnostic and prognostic significance. A tumor-like accumulation of calcium phosphates (metastatic extravascular calcification) in the hip region of a patient with severe secondary hyperparathyroidism has become particularly important in the last two decades, when for most patients the classic radiographic evidence of bone loss has lost its relevance. Precise non-invasive methods for assessing the osteorheptive effect of chronic parathyroid hormone excess in such conditions help prevent serious complications from the skeleton, predict an unfavorable development of the disease, prevent prolongation with surgical treatment.

In the world, a method of studying bone mineral density with the help of dual X-ray absorptiometry (Dual X-ray absorptiometry - DXA) has spread. The device is a computerized complex containing two X-ray sources of different energy levels directed to the parts of the patient's skeleton. After subtracting radiation absorbed by soft tissues, the absorption of bone energy by energy from each radiator is calculated and the final index of bone mineral density is calculated. This method is not only the most accurate, standardized, but also does not carry the risk of irradiation due to the minimal dose loads (about 1 μSv). Usually, the research is aimed at studying the mineral density of the skeleton areas most susceptible to fractures due to osteoporosis (thigh, vertebrae, ray), but it can also measure bone density of the whole organism. It is important not only to register a decrease in bone mineral density, but also to accurately assess this decrease, as well as the response of the bone system to treatment and the dynamics of changes in monitoring patients.

Other methods for determining bone mass and density are known and are being used in practice. These include peripheral DXA (pDXA), which conducts the densitometry of peripheral bone fragments (fingers, wrist, heel); peripheral quantitative computed tomography (pQCT), which requires special equipment and is used mainly for research purposes to study cortical and spongy bone material; Quantitative computed tomography on conventional equipment, but with special volumetric programs (although it carries more radiation with it, it can serve as an alternative to DXA); ultrasonic quantitative densitometry aimed at the study of distal bone fragments (heel bone, elbow, wrist), using an approximate evaluation of bone mineral density by changing the ultrasonic wave transmission speed (used as a screening and evaluation method, gives a calculated index equivalent to the T-test); radiographic absorptiometry (or photodensitometry) using conventional X-ray radiation to photograph finger bones of the hand with subsequent program analysis of images; Single X-ray absorptiometry (with one X-ray source) is used to study the density of peripheral bone segments (heel bone, wrist) submerged in an aqueous medium.

For the diagnosis and treatment of osteoporosis, only dual X-ray absorptiometry is recommended by WHO specialists for clinical use.

It is important to understand the basic indicators of bone densitometry. These are the T-test and the Z-test. The T-test demonstrates the mineral density of the bone substance of an individual when compared to the average of a group of healthy young adult volunteers who are considered to have reached peak bone mass (usually women 30-40 years old).

The deviation from the mean, measured by the number of standard deviations in the simple distribution diagram, will determine the numerical characteristic of the T-test.

In 1994, the WHO working group developed a classification of osteoporosis based on the bone mineral density index obtained by double x-ray absorptiometry. The four proposed classification categories reflect the overall risk of fractures throughout life:

• norm: the bone mineral density in the proximal part of the femur is within 1 standard deviation below the average reference value of young adult women - the T-test is greater than -1;
• low bone mass (osteopenia) - T-test in the range -1 ...- 2,5;
• osteoporosis - the T-score of the femur is lower than -2.5 compared to young adult females;
• severe osteoporosis (or clinically manifested osteoporosis) - T-test less than -2.5 and there are one or more fractures associated with pathological brittleness of bones.

Another key indicator used in studying the mineral density of bones is the Z-test, which compares the state of the bone substance of an individual with the age-appropriate, sex, ethnic group relative norm. Thus, the Z-criterion makes it possible to estimate how the individual mineral density of bones correlates with the expected index for a given age and body weight.

Both indicators (T- and Z-criteria) are used in the guidelines for the treatment of primary hyperparathyroidism. However, if in the first NIH consensus (1991) it was proposed to evaluate the indications for surgery only on the basis of the T-test (less than -2), then in the following it is important to study the Z-criterion for premenopausal women and men younger than 50 years .

Due to the fact that the osteorheptive effect of the parathyroid hormone is most pronounced in a compact bone substance, namely in the distal part of the radius bone, less in the femur containing equal amounts of compact and spongy substance, and even less in the vertebrae, for densitometry in patients with hyperparathyroidism it is recommended to use all these three points.

As the criteria that determine the indications for surgery for asymptomatic primary hyperparathyroidism, the last manual of the National Institutes of Health uses the T-score -2.5 or less for post- and perimenopausal women and men over 50 years of age when examining the lumbar vertebrae, the femoral neck, femur or lower third of the radius. For premenopausal women and men under the age of 50 years, the use of the Z-criterion in the value of -2.5 or less is more appropriate.

[23], [24], [25], [26], [27], [28]

Methods of visualization of hyperfunctioning parathyroid glands

The last two decades were marked by revolutionary changes in the clinical application of modern methods of visualization of the parathyroid glands. Classical parathyroidology is skeptical about the importance of visualization methods for diagnosis and improvement of the effectiveness of primary hyperparathyroidism treatment. In the consensus guide to the treatment of asymptomatic hyperparathyroidism in 2002, the well-known postulate that the best technology for detecting parathyroid glands is the presence of an experienced surgeon undertaking a traditional operation with the revision of all four parathyroid glands was again confirmed.

An example of the effectiveness of such an approach may be the experience of one of the coryphaees of modern endocrine surgery JAvan Heerden, which gives unrivaled results (99.5%!) For surgical cure of patients with primary hyperparathyroidism in a series of 384 consecutive operations using traditional methods over a two-year period, or technical means of preoperative visualization of parathyroid adenomas.

However, the development of new imaging methods, primarily parotyroid gland scintigraphy using the 99mTc-MIBI radiopharmaceutical, provides a unique opportunity to verify the ectopic location of the parathyroid adenoma before surgery, which in itself can not but attract surgeons.

As methods of visualization of parathyroid glands are used:

• ultrasonography in real time with Doppler study;
• scintigraphy of parathyroid glands with various radiopharmaceuticals and isotopes;
• spiral computed tomography;
• Magnetic resonance imaging;
• angiography of the vessels of the parathyroid glands;
• positron emission tomography.

The most accessible and attractive, because of the possibility of a volumetric and structural study of the pathological parathyroid gland, is an ultrasound study that can reveal hyperplastic parathyroid glands larger than 5-7 mm in size with cervical localization. The drawbacks of the method include its uselessness with a traumatic (intrastimic or mediastinal) arrangement of adenomas, as well as a direct-proportional dependence of the success of localization on the size of the gland and the experience of the doctor. The sensitivity of the method of sonography for visualization of hyperfunctioning parathyroid glands averages 75-80% (from 40% to 86% according to different data). The specificity of the method is much lower (35-50%), due to a variety of objective and subjective factors (the presence of an enlarged thyroid gland and nodal formation in it, the phenomenon of autoimmune thyroiditis, cervical lymphadenitis, cicatricial changes associated with previous operations, individual features of the anatomical structure of the neck, experience and the intuition of a sonographer).

The latter factor currently plays a decisive role in Ukraine. With the widespread dissemination of ultrasound devices in cities and towns, in specialized and non-specialized institutions, the ubiquity of doctor-sonographers with thyroid problems remains with virtually no experience of diagnosis of primary hyperparathyroidism and enlarged parathyroid glands. After all, even with the occasional detection of a suspicious parathyroid adenoma, around the neck, thousands of new patients would be diagnosed every year, given the huge mass of thyroid gland examinations (often unreasonable and useless) that are carried out in polyclinics, diagnostic centers and hospitals. In fact, it is necessary to deal with long-term (sometimes - within 5-10 years) ultrasound monitoring of thyroid nodules, often even with puncture biopsies of the latter (!), Which in reality are parathyroid adenomas.

The presence of constant feedback between physicians-sonographers, endocrinologists and surgeons within the framework of one specialized institution, in conditions when it is possible to trace the verification of the diagnosis of primary hyperparathyroidism from suspicion (according to sonography) to laboratory and intraoperative confirmation, allows to significantly improve the competence of physicians and the effectiveness of ultrasound diagnosis of enlarged parathyroid glands. It is necessary to maximally encourage the practice of intra- and inter-agency improvement of physicians, send ultrasound doctors, investigating the neck organs, to advanced training courses in specialized endocrinological medical centers.

Ultrasound examination of the parathyroid glands is performed in a position where the patient lies on his back with a slightly upturned head and a small ridge under the shoulders (the latter is especially important with a short neck). A linear transducer (similar to a thyroid sensor) with a frequency of 5-7.5 MHz is used, which allows to ensure an optimal depth of study of 3-5 cm. Scanning is carried out systematically, bilaterally and comparatively for both sides. First, a lateral scan is performed, then a longitudinal scan. Initially, the area of the typical location of the parathyroid glands is investigated - from the long neck muscles to the thyroid gland in the front and from the trachea medially to the carotid arteries laterally.

Then the study continues on a wider range, capturing submandibular areas, vascular bundles of the neck and anterior-superior mediastinum (for this the sensor is immersed in the jugular incision as much as possible). On the left, it is necessary to investigate the parasophageal space, for which the patient's head rotates in the opposite direction. The linear dimensions of parathyroid glands, as well as their shape, echogenicity, homogeneity and location are studied. At the end, the study is supplemented by color Doppler mapping to assess vascularization, interposition with large vessels. In addition, the structure of the thyroid gland is studied, the presence of focal formations in it, the possible intrathyroid location of the parathyroid glands.

In typical cases, the ultrasound picture with a single adenoma of the parathyroid gland is sufficiently characteristic and has a number of specific features. An experienced researcher can not only detect parathyroid adenoma (or significant hyperplasia) and differentiate it from thyroid nodules and lymph nodes of the neck, but also determine its probable accessory to the upper or lower parathyroid glands. And the last question is solved not so much by the height of the location of the pathological substrate along the longitudinal axis of the thyroid lobe as by the spatial relationships with the posterior surface of the thyroid gland, the trachea and the esophagus.

Adenomas emanating from the upper parathyroid glands are located, as a rule, at the level of the upper two thirds of the thyroid lobe, adjacent to the posterior surface, often occupying the space between the lateral surface of the trachea and the posterior-medial surface of the thyroid gland. In this case, parathyroid adenoma is formed by pressure on it of these neighboring organs and, being much softer and more tender in texture, gets polygonal irregular irregularities (often triangular, sometimes rounded with constrictions from vessels passing by or recurrent laryngeal nerve usually located on the ventral surface such an adenoma).

A typical sonographic picture of the parathyroid adenoma is a small (1-2 cm), clearly delineated hypoechoic formation of an irregularly ovoid form with an intensified intrahepatic blood flow, located behind the thyroid gland, separated from it by a fascial interlayer. Adenoma (hyperplasia) of the parathyroid gland is characterized by a very low echogenicity, which is always below the echogenicity of the thyroid gland, sometimes almost indistinguishable from the echogenicity of cystic fluid formation. The echo structure of the parathyroid tissue is very tender, fine-grained, often completely homogeneous.

Exceptions are long-existing adenomas with secondary changes (sclerosis, hemorrhages, calcifications) or malignant tumors, which, as a rule, are large (more than 3-4 cm) and are accompanied by a clinic of severe hypercalcemia. Difficulties may arise in the differentiation of the intrathyroid adenoma of the parathyroid gland and thyroid nodes.

It should also be remembered that the natural migration of the adenomas of the upper parathyroid glands occurs in the direction of the superior posterior mediastinum, to the left along the tracheo-esophageal furrow, to the right-retro-tracheal in front of the spine. The lower adenomas migrate into the anterior premiginal mediastinum, being located in a more surface plane with respect to the anterior thoracic wall.

Pathologically enlarged lower parathyroid glands are usually located near the lower poles of the thyroid gland, sometimes along the posterior, sometimes along the anterior-lateral surface.

In 40-50% of cases they are in the thyreotymic tract or the upper poles of the thymus. In general, the more superficial is the adenoma, the more likely that it comes from the lower parathyroid glands.

Puncture biopsy of the adenomas of the parathyroid glands is an undesirable element of a patient's examination because of the possible parathyroidism (seeding by tumor cells) surrounding the cellulose. However, if such a study was conducted (differentiation with thyroid nodules), then the probable similarity of the cytological pattern to colloidal or atypical (suspicious for cancer) thyroid nodes should be considered. A differentiating criterion in such cases would be a coloration for thyroglobulin or parathyroid hormone, but the real possibilities of such studies are very limited and require at least an initial suspicion of the presence of hyperparathyroidism.

The second in frequency of application and the first for diagnostic imaging capabilities - radioisotope scintigraphic examination of parathyroid glands with the use of radiopharmaceutical 99mTc-MIBI.

Earlier, in the 80-90s of the 20th century, a study of parathyroid glands with a thallium isotope (201T1) was used alone or in the method of subtraction of images together with scintigraphy with 99тТс with sensitivity of about 40-70%. With the discovery in the early 1990s of the selectivity of absorption by the parathyroid tissue of the radiopharmaceutical 91raTc-M1B1, an isotope of technetium coupled to methoxy isobutyl-isonitrile (cationic lipophilic isonitrile derivative), other isotope preparations lost their importance. Scintigraphy with 99raTc-MGV1 has a certain functional character, although it is not absolutely specific for parathyroid tissue, since the organically bound isotope has a tropicity to other tissues with high mitochondrial activity (in the neck region it is the thyroid and parathyroid glands, salivary glands). The images obtained during scanning can be a static flat image or be combined with a computer tomography (so-called single photon emission computerized tomography (SPECT) or single photon emission computerized tomography (SPECT), which gives a three-dimensional image.

To obtain images of parathyroid glands, either a two-phase protocol is used, or a two-hatch (subtraction, based on subtraction of images) protocol. The two-phase protocol is based on a different rate of leaching of the isotope from the thyroid and parathyroid glands. Static images are taken at 10-15, 60 and 120 minutes of the study after iv introduction of 740 MBq 99gA-M1B1. Positive result is the delay of the isotope in the area of possible localization of parathyroid adenoma on delayed images. It is important to take pictures at the 60th and 120th minutes (in Ukraine, the 120-minute interval is mainly used), since the rate of leaching of the isotope can vary in a significant range (Figure 10.14).

The subtraction protocol of scintigraphy is based on the "subtraction" of the image obtained with the use of 99mTc-MIBI (accumulates both thyroid and parathyroid glands) images of the thyroid gland obtained with the use of the triple isotope alone; preferable to use iodine-123 (in Ukraine because of the high cost of the latter is used by technetium-99m-pertechnetate sodium). For this purpose, initially, 12 MBq of iodine-123 is prescribed 2 hours before the study. Two hours later, the first scan was carried out, then 740 MBq of 99mTc-MIBI was introduced and the scanning was repeated. The image is evaluated after "subtracting" images normalized by the patient's position. Positive is the focus of accumulation, obtained after "subtraction".

SPECT (or OPEST) -investigation is allowed to be performed in both variants of scintigraphy protocols 45 minutes after the injection of 99mTc-MIBI. Scanning captures not only the neck area, but also the area of the mediastinum and thorax. A tremendous advantage of the method is the opportunity to assess the relative position of the thyroid and parathyroid glands, as well as foci of ectopic accumulation of the isotope with their exact attachment to the anatomical structures.

The "posterior" location of the isotope accumulation center relative to the frontal plane of the thyroid gland on the scintigram corresponding to the upper parathyroid gland

Foci of local isotope accumulation are classified as posterior and anterior (in relation to the posterior surface of the thyroid gland), which is more informative. The frontal plane passing through the tip of the lower pole of the thyroid gland divides the foci of the isotope capture from the anterior (almost always correspond to the upper parathyroid glands) (most often correspond to the lower parathyroid glands.

Serial shots in the EPECT study are much more accurate than planar scintigraphy.

The use of parathyroid scintigraphy becomes especially important in repeated operations on the neck, after one or more unsuccessful attempts at surgical treatment of primary hyperparathyroidism, with relapses of the latter or suspected metastases of parathyroid carcinoma.

The effectiveness of the method reaches 80-95%, but it decreases significantly with low hormonal activity and adenoma size, with parathyroid gland hyperplasia or lesions of several glands. Thus, the sensitivity for detection of single parathyroid adenomas reaches 95-100%, with hyperplasia of the gland is reduced to 50-62%, and for multiple adenomas - up to 37%. In this case, one should remember the possibility of false-negative data in a double adenoma, when a large and more active tumor dominates the image and simulates a single lesion, although the correct detection of double adenomas is not uncommon.

Currently, other radiopharmaceuticals that promise greater diagnostic efficacy compared with 99mTc-MIBI are the compounds of technetium-99t with tetrofosmin and furifosmine, but they have not yet been introduced into clinical practice.

Other visualization methods of investigation have significantly less sensitivity, much less specificity and are used mainly in the ineffectiveness of the above methods.

Thus, spiral multidetector computed tomography with the use of 3 mm slices and in / in contrast enhancement (it is necessary to remember the difficulty of subsequent radioisotope investigation of the thyroid gland).

Magnetic resonance imaging has no significant advantages over computed tomography and is less commonly used. Its disadvantages include, as in the case of computed tomography, the appearance of artifacts associated with swallowing, breathing and other movements of the patient, as well as low specificity of the results. Typically, parathyroid adenomas exhibit an increased signal intensity at T2-weighting and iso-intensity at a T1-weighted signal. It is possible to amplify the signal when contrasting with gadolinium.

Angiography of vessels feeding the parathyroid glands is used casuistically rarely and predominantly in the unsuccessful localization of a recurrent or persistent tumor (sometimes in conjunction with blood sampling to determine the relative concentration of parathyroid hormone from the right and left jugular veins to localize the side of the lesion).

Extremely popular and promising in recent years is the method of positron emission tomography (PET), which already at the first comparative studies with 11T-fluorine-deoxy-glucose (FDG) showed higher sensitivity compared to scintigraphy, as well as using n -O-methionine. The obstacle to widespread introduction of the PET method remains the high cost of the study.

In the last few years, there have been reports of the possibility of combining (computer fusion-fusion) images obtained with several imaging techniques - scintigraphy, computed tomography, PET, angiography, sonography. Such a "virtual" image, according to a number of authors, has significantly increased the effectiveness of treatment of relapses of primary hyperparathyroidism.

In addition to the previously mentioned advantages of the correct preoperative localization of pathologically altered parathyroid glands, it should be mentioned that the positive and concurrent (ultrasound + ssiutigraphy) results of visualization studies are an indispensable condition for performing mini-invasive surgical interventions in primary hyperparathyroidism that have become so popular in the last decade (in specialized clinics at the share of these operations is 45-80% of all interventions).

Treatment of the primary hyperparathyroidism

The lack of an effective alternative to the surgical treatment of primary hyperparathyroidism, as well as the destructive effect of the disease on many body systems with its long flow, make surgery the only true tactical option for managing patients after diagnosis. This is also facilitated by progress in improving the technique of surgical treatment of primary hyperparathyroidism, a high cure rate (up to 99%) and a low risk of complications.

The experience of the surgeon in operations on the parathyroid glands, as well as 80 years ago (with the formation of parathyroid surgery), remains the main factor determining the success of surgical intervention by the factor. This is clearly illustrated by the following statements of the coryphaees of the study of primary hyperparathyroidism.

"The success of parathyroid surgery should be based on the ability of the surgeon to recognize the parathyroid gland when he sees it, to know the probable places of the secretive arrangement of the glands, and also its delicate technique of operating which will make it possible to apply this knowledge."

"Detection of the parathyroid gland adenoma by an experienced parathyroid surgeon is more effective than using preoperative imaging tests; Parathyroidectomy should be performed only by the most experienced surgeon-experts in this field, they are responsible for the preparation of a new generation of experts in parathyroid surgery. "

"Parathyroid surgery requires the participation of only an experienced specialist in this field, otherwise the frequency of unsuccessful operations and the level of complications will be unacceptably high."

The goal of surgical intervention is to remove one or more pathologically enlarged parathyroid glands, ensuring the restoration of permanent normocalcemia. The operation should be accompanied by a minimal possible injury of surrounding tissues and normal parathyroid glands.

Despite the obvious advantages of rapid and effective treatment of primary hyperparathyroidism by surgery, the question of weighted determination of indications for surgery remains relevant for a number of patients. The reason for this were several circumstances: an increasing number of low-symptomatic or asymptomatic cases of the disease, very slow progression in 2/3 patients with an asymptomatic variant of the disease, potential (albeit low) risks of surgical intervention and anesthesia that may increase in intercurrent pathological conditions. The importance of this aspect of the problem is confirmed by three international consensus guidelines for the management of patients with asymptomatic primary hyperarteriatosis, prepared under the auspices of the National Institutes of Health (NIH) and published in 1991, 2002 and 2009. Of course, for Ukraine this issue is not so acute today, because in the main there are still quite bright cases of the disease, often in a neglected state, when there are no alternatives to surgical treatment. However, with the wide introduction of screening for primary hyperparathyroidism, we will inevitably face the fact of the existence of a large number of patients with "mild" forms of the disease, the risk of surgery for which, due to age or other health problems, may be higher than the potential benefits of surgical cure.

Indications for operation

The operation is indicated for all clinical symptom forms of primary hyperparathyroidism, that is, in a laboratory-confirmed disease that has typical clinical manifestations or consequences of long-existing hypercalcemia or elevated parathyroid hormone levels.

On clinical manifestations, we stopped in the corresponding section. It should only be recalled that, with careful questioning and examination of the patient, registration of subtle disturbances of the psychoneurological condition, only a few cases will remain for the true asymptomatic variants of the disease.

Pregnancy is not a contraindication to surgical treatment. Pregnancy in the second trimester, but in the case of severe hypercalcemia, pregnancy does not play a role in connection with the transplacental negative effect of high calcium levels and the risk of complications for the fetus (80%), the threat of miscarriage, labor weakness and other complications for the mother (67% ). The operation in the last weeks of pregnancy is indicated for critical hypercalcemia with simultaneous consideration of the issue of delivery by caesarean section.

The higher the level of calcium in the blood, the more urgent the operation should be, since it is very difficult to predict the development of a hypercalcemic crisis - a potentially fatal complication.

Patients with severe renal dysfunction should be operated under the conditions of the possibility of hemodialysis in connection with the risk of temporary deterioration of renal filtration.

When choosing the treatment tactics for patients with a true asymptomatic course of primary hyperparathyroidism, one should rely on the recommendations of the international working group first collected under the auspices of the National Institutes of Health of the USA in 1990. The third revision of such recommendations, which was held at the meeting in 2008, was stated in the press in 2009 It will be interesting to follow trends in the treatment of asymptomatic hyperparathyroidism over the past 20 years by comparing previous and current recommendations.

The authors repeatedly emphasize in these recommendations that only surgical treatment is exhaustive and definitive, therefore, when selecting the observational therapeutic tactics, it is important not only to strictly adhere to the proposed criteria, but also to take into account the need for regular monitoring of the main indicators (level of calcium, parathyroid hormone, glomerular filtration rate or creatinine clearance , as well as the dynamics of bone mineral density) at least once a year.

In addition, attention should be paid to the fact that for patients younger than 50 years, surgery is always preferable, as a steady decrease in bone mineral density with an increased risk of fractures and a lifelong risk of developing other irreversible systemic changes is more relevant for patients of this age. Another serious criterion is the degree of hypercalcemia. The level of calcium exceeding the upper limit of the norm by more than 0.25 mmol / l (ie> 2.8 mmol / l) is incompatible with the concept of asymptomatic primary hyperparathyroidism and the choice of a different, but surgical, treatment tactic.

Particular influence is given to the characteristic of renal function. In accordance with the recommendations of K / DOQI, it was decided to evaluate the estimated glomerular filtration rate of less than 60 ml / min (ie, stage 3 of chronic kidney disease) as a serious argument in favor of surgery, despite the fact that the causes affecting kidney function , can be associated not only with hyperparathyroidism.

The most argued are the provisions concerning the need for surgery in the case of progressive osteoporosis in primary hyperparathyroidism. They are based on several randomized controlled studies that support the view that a progressive decrease in bone mineral density is observed with mild asymptomatic primary hyperparathyroidism and, on the other hand, that only surgery can stop development and lead to regression of osteoporosis in a disease such as primary hyperparathyroidism.