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Review Article



Atypical Thyroid Function Tests, Thyroid Hormone Resistance [Atipik Tiroid Fonksiyon Testleri: Tiroid Hormon Direnci]

Soner Cander, Ozen Oz Gul, Canan Ersoy.




Abstract

The assessment of thyroid function tests for to the diagnose hyperthyroidism (thyrotoxicosis) or hypothyroidism does not constitute a nuisance when the clinical suspicion is strong. However, substantial proportion of discordant results with clinical findings or atypical results possible to come across in the thyroid function tests. In such cases, accurate diagnosis is very important for appropriate management to the patient, prevention of unnecessary tests and cost increases. For accurate diagnosis in these patients, a detailed clinical evaluation with specific laboratory studies are needed. Atypical hyperthyroxinemia (high thyroid hormone levels are incompatible with TSH) is an atypical thyroid function test pattern can be seen in the rare cases of thyrotropin releasing pituitary adenoma or thyroid hormone resistance syndrome. However, in this case, assay interferences and euthyroid situations such as thyroxin replacement therapy with poor-compliance, euthyroid sick syndrome including acute psychiatric disorders, hyperthyroxinemia due to drugs like heparin, disorders with protein binding abnormalities (familial dysalbuminemic hyperthyroxinemia, transthyretin related hyperthyroxinemia) which are seen more common, should be excluded primarily. Then should be consulted further examinations for the differential diagnosis of thyrotropin-secreting pituitary adenomas and thyroid hormone resistance syndrome. The Refetoff Syndrome is developing due to a defect in the beta-receptor and is most common in thyroid hormone resistance syndromes. It includes a combination of findings of hyperthyroidism and hypothyroidism and suggests an autosomal dominant inheritance feature. Therefore, family screening should be done in patients diagnosed. Mostly, beta blockers is sufficient in the treatment. Other rare syndromes of thyroid hormone resistance that occurs due to alpha-receptor defects, thyroid hormones membrane transport defect and thyroid hormone metabolism defect related with deficiency of deiodinases. The clinical pictures of this rare syndromes are more severe compared to classic syndrome and often the choice of treatment is only supportive therapy.

Key words: Thyroid function tests, atypical TFT, thyroid hormone resistance






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