Metabolic and Cardiovascular Responses to Exogenous Triiodothyronine Favour Nontreatment of a Girl with Familial Receptor-Positive Thyroid Hormone Resistance

. A father and daughter with inappropriate TSH secretion due to generalized relative receptor-positive thyroid hormone resistance are described. Minor variations of tissue peripheral resistance were observed in the adolescent girl. Shortened ankle reflex relaxation time and other clinical signs were consistent with a mild hyperthyroid state of the neuromuscular unit. The response of sex hormone-binding globulin concentration, 24 hour-ECG data and left ventricular echocardiographic parameters to increasing doses of triiodothyronine confirmed an euthyroid state of heart and liver tissue in the presence of excess thyroid hormone. Based on these findings and the benign course of the disease, treatment was withheld. Careful assessment, including echocardiography and 24 hour-ECG, of the functional state of thyroid hormone target tissues during triiodothyronine administration is recommended in these patients. No treatment is required when the functional state of the target tissues is eumetabolic.