Endocrine Abstracts

Resistance to thyroid hormones (RTH) is a genetic syndrome characterized by reduced responsiveness of target tissues to thyroid hormones (TH) and accompanied by normal or slightly high TSH values with high serum concentrations of fT₄ or fT₃. We present two cases of RTH, one pituitary and one generalised resistance.

Case 1: A 31 y.o. male presented with thyrotoxicosis symptoms and a biochemical profile showing increased serum fT₄ 28.02 pmol/l (N 12–22) and T₃ 209.7 ng/dl (80–200) but normal TSH (4.33 mUI/l); he had a small goitre, increased SHBG and ATPO was negative. His CT scan revealed a pituitary microadenoma of 7/4 mm, but TRH test documented increasing TSH with 10 mUI/l from baseline to a maximum at 20 min. He was diagnosed with RTH syndrome with hyperthyroidism and started on Methimazole and beta blockers, with good clinical and biochemical response at follow-up.

Case 2: A female aged 57 with a small goiter, obesity, dyslipidaemia, glucose intolerance, infiltrated skin was diagnosed with subclinical hypothyroidism – TSH 7.41 mUI/l, normal fT₄, and negative ATPO. She was given 50 μg/day L-thyroxine and had normal thyroid profile for one year, when she presented with very high fT₄ values (61.96 pmol/l-N 10.6–19.4) and a TSH in the upper limit, with the same clinical and biochemical features, suggestive of hypothyroidism. TRH test confirmed RTH syndrome, in a generalized form considering the clinical and biochemical profile. She is well under L-thyroxine treatment in the same dose. The genetic determination was not available in the two cases.

Conclusion: Despite rare, RTH syndrome should be considered when there are mismatches between the clinical and the thyroid functional profile.