The syndrome of resistance to thyroid hormone, misdiagnosed as thyrotoxicosis

Abstract EN

Objective: to report two cases of resistance to thyroid hormone to increase the awareness of this syndrome, which is frequently misdiagnosed and incorrectly treated.

Methods: we described two siblings, both of whom were diagnosed as having thyrotoxicosis and one of them was treated with carbamazole and subsequently developed hypothyroidism.

Both patients showed features of resistance to thyroid hormone and required additional L-thyroxine to normalize the thyroid stimulating hormone level while remaining clinically euthyroid.

Results: Laboratory evaluation revealed increased serum thyroxine and tri-iodothyroxine levels as well as increased thyroid stimulating hormone (TSH) levels.

The free alpha subunit/TSH ratio was normal, and CT of the pituitary gland showed no tumour.

Metabolic studies using graded doses of tri-iodothyroxine supported the diagnosis.

Conclusion: The two patients have resistance to thyroid hormone but were erroneously diagnosed as thyrotoxic and one of them inappropriately treated.

Patients with elevated plasma levels of thyroid hormones with high or normal TSH level need careful evaluation of the hypothalamic-pituitary function & peripheral action of thyroid hormones.

Key words: Thyroid function, hypothyroidism, TSH, goitre