Peripheral insensitivity to thyroid hormones in a euthyroid girl with goitre.

A 9-year-old girl was euthyroid with a small goitre, exophthalmos, scaphocephalic skull, minor sketelal abnormalities, and raised serum thyroid hormone concentrations. Other members of the family did not have goitres and their thyroid hormone levels were normal. From age 3 years the patient was treated for Graves's disease, but after 4 years treatment was stopped because of enlargement of the goitre. Despite increased serum thyroxine (T4), free T4 (FT4), and triiodothyronine (T3), basal serum TSH, and the TSH response to thyrotropin-releasing hormone (TRH) were normal. Pituitary refractoriness was present because full suppression of the TSH response to TRH was achieved only after daily administration of 500 micrograms thyroxine. Urinary excretion of hydroxyproline, and the activity of red cell glucose-6-phosphate dehydrogenase remained normal when excess T4 was administered, demonstrating the tissue resistance to thyroid hormones. Peripheral lymphocytes were found to have nuclear receptors for T3 with normal affinity, but the relatively low binding capacity indicated that the biochemical defect might be a deficiency of nuclear receptor protein. The findings in this patient differ somewhat from previously reported cases of peripheral resistance to thyroid hormones.