Effective TRIAC treatment of a THRβ-mutated patient with thyroid hormone resistance.

Resistance to thyroid hormone (RTH) is a rare autosomal dominant disease characterized by an alteration of thyroid hormone negative feedback, usually as a consequence of a mutation in the thyroid hormone receptor-b gene (THRβ). It is characterized by high variability of clinical manifestations, ranging from isolated abnormal thyroid function tests without symptoms to severe and impaired clinical conditions. Here we report the case of a woman who was diagnosed with RTHβ when she was 35 years old and was treated with 3,5,3-triiodiothyroacetic acid (TRIAC) because of the onset of clinical symptoms of hyperthyroidism. This therapy has been effective in controlling thyrotoxicosis for 5 years. After this time the patient developed an autoimmune hyperthyroidism, with TSH receptor autoantibodies appearance, which caused a loss of efficacy of the drug in controlling the disease. The development of different pathophysiological mechanisms of thyrotoxicosis, as in this case, could be the reason for both variability of disease manifestations and of loss of response to drug therapy.