Subclinical hyperthyroidism: diagnostic criteria and principles of treatment
Keywords:thyroid, thyroid stimulating hormone, hyperthyroidism, thyrotoxicosis, subclinical hyperthyroidism, Graves’ disease, toxic multinodular goiter
This article presents the European Thyroid Association guidelines for diagnosis and treatment of subclinical hyperthyroidism, 2015. Determination of thyroid-stimulating hormone levels can help to diagnose a variety of pathological conditions: disorders of sexual development, amenorrhea (primary or secondary), infertility, miscarriage, which require specific treatment after detection of hormonal status disorders (subclinical, overt), taking into account the patient’s age.
Diagnosis of endogenous subclinical hyperthyroidism is based solely on the results of laboratory tests, not clinical criteria. Endogenous subclinical hyperthyroidism is defined by the presence of sub-normal levels of thyroid-stimulating hormone with normal levels of free thyroxine, total triiodothyronine, and/or free triiodothyronine. There are two categories of endogenous subclinical hyperthyroidism: class 1 – the level of thyroid-stimulating hormone is 0.1–0.39 mIU/l; class 2 – the level of thyroid-stimulating hormone is < 0.1 mIU/l. The levels of free thyroxine and free triiodothyronine, as a rule, are medium-high value at a subclinical level of thyroid hormone and can help differentiate between endogenous subclinical hyperthyroidism from overt hyperthyroidism.
Not recommended to study the thyroid-stimulating hormone level as the first test for the diagnosis of subclinical hyperthyroidism. In identifying low levels of thyroid-stimulating hormone it is necessary to investigate the level of free thyroxine, free and bound triiodothyronine.
Patients with primary sub-normal levels of thyroid-stimulating hormone with concentration of thyroid hormones in the upper limit or in normal range should be evaluated within 2–3 months.
It is recommended to perform scintigraphy and possible 24-hour test the absorption of radioactive iodine if in patient with 2nd degree endogenous subclinical hyperthyroidism there is nodular goiter to determine treatment strategy.
Ultrasonography with color Doppler can be informative in patients with endogenous subclinical hyperthyroidism and nodular goiter.
Determining the level of antibodies to thyroid-stimulating hormone receptors can confirm the etiology of autoimmune-induced hyperthyroidism.
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