Peripheral resistance to thyroxine: a cause of short stature in a boy without goitre

A euthyroid pubertal boy was investigated for short stature and was found to have an elevated serum thyroxine and delayed bone age. In spite of high thyroxine levels, there were no clinical signs of hyperthyroidism and kinetic studies revealed a normal rate of thyroxine metabolism. Plasma TSH levels were elevated but there was no goitre. Administration of up to 900 mug of thyroxine or 225 mug of triiodothyronine led to minimal changes in urinary hydroxyproline excretion, pulse rate and body weight. These observations indicate that this boy has a target organ insensitivity to thyroid hormones. When compared with other patients with this disorder, the studies further emphasize that this condition may have a variable clinical presentation. In addition, the extent of the target organ defect may not be evident from routine clinical and laboratory observations. The possible molecular basis of the defect is discussed.