Resistance of peripheral tissues and pituitary to thyroid hormone.

We describe a 29-year-old male with thyroid hormone resistance. He was first seen because of a goiter, and was considered to have hyperthyroid Graves' disease. Despite subtotal thyroidectomy followed by radioiodine therapy, serum thyroxine levels were elevated with high serum TSH levels. Baseline thyroid function showed serum thyroxine of 16.6μg/dl, free thyroxine of 4.60 ng/dl, triiodothyronine of 197 ng/dl, and TSH of 34μU/ml. Triiodothyronine administration by gradually increased doses of 75, 150, 225, 300, and 375μg/d over a 25-day period resulted in gradual reduction of serum TSH and T4 levels, but serum TSH still responded to TRH even during this period. The basal metabolic rate was-14% and showed a minimal rise even with large doses of triiodothyronine. The results led to the diagnosis of generalized thyroid hormone resistance including the pituitary gland. Increased pulse rate, finger tremor and emotional lability in the patient suggest that the severity of peripheral refractoriness to the hormone may vary from tissue to tissue. In addition, a reduced thyroidal responsiveness to TSH as a consequence of inappropriate radioiodine therapy was observed in this patient.