Diagnosis of acromegaly and gigantism
Last reviewed: 23.04.2024
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When diagnosing acromegaly, it is necessary to take into account the stage of the disease, the phase of its activity, as well as the shape and features of the pathological process. It is expedient to use the data of X-ray study and methods of functional diagnostics.
When radiographing the bones of the skeleton, the phenomena of periosteal hyperostosis with signs of osteoporosis are noted . The bones of the hands and feet are thickened, their structure is usually preserved. The nail phalanges of the fingers are pagodically thickened, the nails have a rough, uneven surface. Of the other bone changes with acromegaly, the growth of spurs on the calcaneus is constant, somewhat less often on the elbows.
Radiography of the skull reveals true prognathism, discrepancies in teeth, an increase in the occiput and a thickening of the cranial vault. Often, the internal hyperostosis of the frontal bone is detected. Calcification of the dura mater is noted. The accessory nasal cavity, especially the frontal and sphenoid sinuses, are highly pneumatized, which is also observed in the latticed and temporal bones. There is proliferation of air cells of the mastoid processes. In 70-90% of cases, the size of the Turkish saddle increases. The size of the pituitary tumor in acromegaly depends not so much on the duration of the disease as on the nature and activity of the pathological process, as well as the age at which the disease began. There is a direct correlation between the size of the Turkish saddle and the level of somatotropic hormone in the blood and the reverse - with the age of the patients. Due to the growth of the tumor, the destruction of the walls of the Turkish saddle is noted. The absence of radiographic and ophthalmological signs of a pituitary tumor does not exclude its presence in acromegaly and requires the use of special tomographic methods of investigation.
The thorax is deformed, has a barrel shape with dilated intercostal spaces. Develops kyphoscoliosis. For the spine, the disappearance of the "waist" in the ventral areas of the thoracic vertebrae is characteristic, multiple contours are observed with the formation of the newly formed bone on the old, beak-like protrusions and paravertebral arthroses. Joints are often deformed with restriction of their function. The phenomena of deforming arthrosis are most pronounced in large joints.
The thickness of soft tissues on the plantar surface of the feet in patients exceeds 22 mm and directly correlates with the levels of STG and IRF-1. This test can be used to determine the activity of acromegaly and a dynamic assessment of the adequacy of the therapy.
Laboratory methods for the study of acromegaly show the following changes in somatotropic function: a disturbance in the physiological secretion of growth hormone, manifested by a paradoxical increase in the content of growth hormone in response to glucose loading, intravenous administration of thyroidiberin, lylyberyrin, there is no increase in somatotropic hormone levels during sleep; a paradoxical decrease in the level of growth hormone during the test with insulin hypoglycemia, the introduction of arginine, L-dopa, dopamine, bromocriptine (parlodel), and also during exercise.
The most common tests that allow to assess the condition of the hypothalamic-pituitary system in acromegaly and the safety of feedback mechanisms include oral glucose tolerance and a test with insulin hypoglycemia. If the normal intake of 1.75 g of glucose per 1 kg of body weight leads to a significant decrease in the level of growth hormone in the blood, then in acromegaly, there is either no reaction / decrease in the growth hormone below 2 ng / ml for 2-3 hours, or a paradoxical increase level of growth hormone.
The introduction of insulin in a dose of 0.25 units per 1 kg of body weight in normal, leading to hypoglycemia, promotes an increase in the content of growth hormone in the serum with a maximum of 30-60 minutes. In acromegaly, depending on the size of the initial level of growth hormone, hyporeactive, areactive and paradoxical reactions are revealed. The latter is manifested by a decrease in the level of somatotropic hormone in the blood serum.
The most characteristic changes that allow using them for diagnostic purposes are manifested at the pituitary level. The formation of pituitary adenoma promotes the formation of less differentiated somatotrophs with an altered receptor apparatus. As a result, tumor cells acquire the ability to respond by increasing somatotropic secretion in response to the effect of nonspecific stimuli for a given cell type. Thus, hypothalamic releasing factors (lylyberin, thyreoliberin), without affecting normal production of growth hormone, in acromegaly activate somatotropic secretion in approximately 20-60% of patients.
To establish this phenomenon, thyreoliberin is administered IV in a dose of 200 μg, followed by blood collection every 15 minutes for 90-120 minutes. The presence of altered sensitivity to tiroliberin, determined with an increase in the level of growth hormone by 100% or more from the initial, is a sign indicating a violation of receptor activity of somatotrophs and pathognomonic for a pituitary tumor. However, in the final diagnosis, it should be taken into account that a similar nonspecific increase in the level of STH in response to the administration of tyroliberin can be observed even in certain pathological conditions (depressive syndrome, anorexia nervosa, primary hypothyroidism, renal insufficiency). In the diagnosis of the tumor process in the pituitary gland, additional research on the secretion of prolactin and TSH in response to the administration of tyroliberin may have some value. The blocked or delayed reaction of these hormones can indirectly indicate a tumor of the pituitary gland.
In clinical practice, a functional test with L-dopa, a stimulant of dopaminergic receptors, has spread. Taking the drug at a dose of 0.5 g orally with the active phase of acromegaly leads not to an increase, as noted in the norm, but to the paradoxical activity of the hypothalamic-pituitary system. Normalization of this reaction during treatment is a criterion of rationality of the therapy.
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