Partial peripheral resistance to thyroid hormone.

A 33 year old partially thyroidectomized woman was euthyroid when ingesting 500 microgram of L-triiodothyronine (T3) daily. Her condition was evaluated during therapy with daily T3 doses between 50 and 500 microgram. She was hypothyroid and had a markedly subnormal oxygen consumption rate when taking 50 to 100 microgram T3 daily, and oxygen consumption did not increase greatly above predicted normal values despite serum T3 concentrations up to 3,200 ng/dl. Her pulse rate, blood pressure, systolic time intervals and exercise tolerance changed minimally and remained within the normal range during the different dosage schedules. Urinary creatine and hydroxyproline, indices of muscle and skeletal protein catabolism, increased normally with higher T3 doses, but serum cholesterol, creatine phosphokinase, calcium and alkaline phosphatase did not change substantially. Basal and thyrotropin-releasing hormone (TRH) stimulated thyrotropin secretion were suppressed during all T3 doses. The prolactin response to TRH was normal at 50 microgram T3/day and was reduced by higher doses of T3. Absorption of T3, serum T3 protein binding and T3 metabolic clearance rates were all within normal limits. The findings in this patient are compared to clinical and biochemical findings in 17 previously described patients. The manifestations of peripheral thyroid hormone resistance are quite variable in the organ systems involved and in the degree of involvement. The molecular basis of the abnormality in our patient remains undefined.