Diagnosis of diffuse toxic goiter

With sufficiently pronounced clinical symptoms, the diagnosis of diffuse toxic goiter is beyond doubt. Laboratory tests help to make a correct and timely diagnosis. Diffuse toxic goiter is characterized by an increase in the basal level of thyroid hormones and a decrease in _TSH. Usually, the basal level of T3 is increased to a greater extent than the level of _T4. Sometimes there are forms of the disease when T3 _is higher, and thyroxine, total and free, are within normal fluctuations.

In doubtful cases, when T3 _and T4 _are slightly elevated and there is a suspicion of thyrotoxicosis, it is useful to perform a test with rifathiroin (TRH). The absence of an increase in TSH with the introduction of TRH confirms the diagnosis of diffuse toxic goiter.

An increase in the basal level of TSH in diffuse toxic goiter is detected in those rare cases when hyperthyroidism is caused by a TSH-producing pituitary adenoma. In this case, against the background of increased levels of T3 _and T4, _high TSH will be determined.

When diagnosing diffuse toxic goiter, the determination of the titer of antibodies to thyroglobulin and the microsomal fraction is of great importance.

An indirect immunofluorescence method for determining antithyroid antibodies has been developed, which can be used to detect four types of antithyroid antibodies (antibodies to microsomal antigen, thyroglobulin, nuclear antigens, and the second colloidal antigen) in the blood of patients with diffuse toxic goiter. In their works, S. L. Vnotchenko and G. F. Aleksandrova showed that classical antithyroid antibodies are markers of the pathological process in the thyroid gland.

The activity of thyroid-stimulating immunoglobulins (TSI) is determined by a biological method based on the increase in cAMP sections of the human thyroid gland.

In addition to the biological method, a method for determining immunoglobulins that inhibit the binding of TSH is used. The most reliable information is provided by their combination with the simultaneous determination of TSH in the blood. As studies have shown, TSI are detected in 80-90% of cases in untreated patients with diffuse toxic goiter. The value of their percentage content does not determine the severity of thyrotoxicosis, does not correlate with the level of thyroid hormones, but can serve as a criterion for the duration of drug therapy. Discontinuation of treatment at a level of thyroid-stimulating immunoglobulins above 35 /o leads to a relapse of the disease. Patients receiving thyrostatic therapy should apparently determine the TSI level at the beginning of therapy and before the expected cancellation of the maintenance dose of the drug. With a long-term elevated level, it is advisable to refer patients for surgical treatment. Maintaining a high TSI indicator is a risk factor for relapse of the disease. After adequate treatment of thyrotoxicosis with thyreostatic drugs or radioactive iodine, the TSI titer decreases in half of the patients, after subtotal resection of the thyroid gland - in 83%. Considering the transplacental penetration of TSI, the determination of the indicator may have diagnostic value in pregnant women to determine the risk of congenital hyperthyroidism.

In recent years, radioisotope examination of thyroid function has been used much less frequently due to the possibility of determining the level of thyroid hormones and TSH. The method is based on the ability of the thyroid gland to selectively accumulate iodine. Its function is assessed by the rate of iodine absorption, its maximum accumulation, and the rate of decline in activity. Radioactive iodine ( ¹³¹ I) is administered orally on an empty stomach in an indicator dose of 1 μCi. Determination of activity after 2 and 4 hours shows the rate of its absorption, after 24-48 hours - maximum accumulation, after 72 hours - the rate of decline.

Absorption of I in thyroid dysfunction, %

Determination time, h	Norm of oscillation	Mild hyperthyroidism	Severe hyperthyroidism	Euthyroid goiter	Hypothyroidism
2 4 24	4.6-13 5.3-22 10.0-34	11-37 14.3-40 25-57	15-69 30-75 31-80	4.4-19 7.3-27 11-37	1-5.8 1-5.6 0.6-9

In healthy individuals, the maximum uptake of radioactive iodine occurs by 24-72 hours and is 20-40% of the indicator dose. In hyperthyroidism, uptake figures are usually increased depending on the degree of thyroid activity, over 40% after 24 hours. In hypothyroidism, ¹³¹ I uptake, as a rule, does not exceed 15% of the indicator dose. When evaluating the results of this test, it is necessary to remember that many drugs can, to varying degrees, reduce ¹³¹ I uptake by the thyroid gland (salicylates, bromides, antithyroid agents, iodine-containing compounds such as enteroseptol, mixase, valocordin, some antibiotics, sulfonamides, mercury diuretics, rauwolfia derivatives, estrogens, glucocorticoids, adrenaline, many hypoglycemic drugs). Radiocontrast iodine-containing preparations are capable of suppressing the uptake of ¹³¹ I to a hypothyroid level for periods ranging from several weeks to several years. In connection with the above, low absorption figures have no diagnostic value without an assessment of clinical manifestations. The diagnostic value of the described study is increased by using the technetium isotope - ^99m Tc.

Radioisotope scanning ( scintigraphy ) of the thyroid gland allows us to identify functionally active tissue, determine its shape and size, and the presence of nodes. In addition, this method can help detect ectopic areas of thyroid tissue that capture isotopes. Scanning is performed 24 hours after taking 1-5 μCi ¹³¹ I or 2-3 μCi ^99m Tc. Diffuse toxic goiter (Graves' disease) is characterized by an enlarged image of the thyroid gland with increased isotope capture.

Ultrasound examination allows determining the size and volume of the thyroid gland, the features of its echostructure. In hyperthyroidism caused by autoimmune processes, a diffuse decrease in the echogenicity of the thyroid tissue is detected.

Among non-specific biochemical blood parameters, hypocholesterolemia and moderate hyperglycemia should be noted.

In the presence of characteristic symptoms of thyrotoxicosis, the diagnosis of diffuse toxic goiter does not present great difficulties. It is more difficult to make a correct diagnosis in cases where symptoms of a disorder of one system predominate, for example, cardiovascular, gastrointestinal tract or mental, and it is necessary to differentiate diffuse toxic goiter (Graves' disease) from the corresponding diseases. Diagnosis is difficult in elderly patients, when, in addition to the symptoms of thyrotoxicosis, concomitant chronic diseases are exacerbated.

In mild forms of thyrotoxicosis, the doctor should conduct differential diagnostics with vegetative-vascular dystopia. Persistent tachycardia, independent of the patient's position and at rest, increased T3, T4 levels _, and _increased thyroid isotope absorption figures indicate hyperthyroidism.

Moderate thyrotoxicosis usually does not cause difficulties in diagnosis. However, in the absence of enlargement of the thyroid gland, eye symptoms and the presence of predominant disorders of the cardiovascular system, there is a need for differential diagnosis with rheumatic myocarditis, heart defects, and TBC intoxication. The diagnosis is confirmed by an increase in the content of thyroid hormones, increased absorption of I, and increased size of the gland.

In severe cases, when almost all internal organs and systems are involved in the process, differential diagnosis with pituitary cachexia, organic lesions of the liver, kidneys, cardiovascular system, and myasthenia gravis is necessary. In addition to the studies indicated above, the presence of pituitary tropic hormones, liver and kidney function are determined; a liver scan is performed, as well as a test with proserin, which allows excluding myasthenia.

Symptoms of toxic adenoma do not differ significantly from those of diffuse toxic goiter (Graves' disease), with the exception of exophthalmos, which is almost never seen in adenoma. The scintigram shows isotope absorption at the site of the palpable compaction with reduced absorption or absence of it in the surrounding tissue. When exogenous TSH is administered, the isotope is concentrated in areas of the gland that did not previously accumulate it, which allows differentiating toxic adenoma from thyroid gland developmental abnormalities.

Hyperthyroidism in de Quervain's thyroiditis, or subacute thyroiditis, is characterized by low isotope uptake. In this case, it is advisable to determine the thyroglobulin level. For example, with an increase in thyroid hormones and low ¹³¹ I uptake figures by the thyroid gland, an increased thyroglobulin level is characteristic of subacute thyroiditis, and a low one is characteristic of thyrotoxicosis.

Hyperthyroidism due to trophoblastic tumors may be suspected in the presence of a history of recent pregnancy, tumor, and high levels of human chorionic gonadotropin.

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