Resistance to thyroid hormone: report of 2 kindreds with 35 patients.
OBJECTIVE
To report two kindreds with resistance to thyroid hormone (RTH), particularly the clinical and laboratory evolution after thyroidectomy and with antithyroid drug treatment.


METHODS
Clinical data and thyroid function were determined in 82 members from three different generations of both families. Unaffected relatives were used as a control group. Response of thyroid-stimulating hormone (TSH) to the hypothalamic thyrotropin-releasing hormone (TRH) was evaluated in five patients and compared with five nonaffected relatives.


RESULTS
Thirty-five (22 male and 13 female) patients had high serum levels of thyroxine and triiodothyronine in conjunction with nonsuppressed TSH. Goiter was present in 66% of affected family members; prevalence was 10% in childhood and 88% in adulthood. The prevalence of goiter was 18% in nonaffected relatives. No patient showed evidence of thyroid hypofunction or hyperfunction, and the TSH response to TRH was similar to that of nonaffected relatives. The incidence of RTH in offspring was 60%, consistent with autosomal dominant transmission. Four patients had undergone thyroidectomy, and two required a second operation because of recurrence of goiter. Patients who had undergone thyroidectomy had normal or near-normal levels of thyroid hormone and very high values of TSH despite thyroid hormone therapy. Five patients were treated with antithyroid drugs for 2 to 10 years, but their thyroid function remained similar to that of nontreated patients.


CONCLUSIONS
RTH is a relatively rare and benign condition that can be misdiagnosed as hyperthyroidism. The disease is responsible for a high prevalence of goiter in affected families. Thyroidectomy and treatment with antithyroid drugs are not indicated and may have lifelong implications.
Anselmo
J
J
Endocrinology Unit, Hospital of Ponta Delgada, Azores-Portugal.
César
R
R