Resistance to Thyroid Hormones: A Disorder Frequently Confused With Graves' Disease

Five patients from two unrelated families were found to have goiter and elevated serum concentrations of thyroxine (T₄) and triiodothyronine (T₃) without symptoms or signs of hyperthyroidism. All had measurable concentrations of thyroid stimulating hormone (TSH), and in four who were tested, there was an increase in TSH concentration following thyrotropin releasing hormone (TRH) administration. We believe these five patients have general resistance to the effects of thyroid hormones and need elevated concentrations of T₄ and T₃ to maintain a eumetabolic state. Study of nuclear T₃ receptors from cultured fibroblasts of one patient disclosed a normal equilibrium association constant and a maximal binding capacity that was greater than normal control values. These findings suggest that thyroid hormone resistance in this patient is not due to a decrease in either the affinity or the number of specific nuclear T₃ receptors. This disorder can easily be confused with Graves' disease and result in inappropriate treatment for hyperthyroidism, as was the case in three of our patients.