Precocious puberty in juvenile hypothyroidism.

Three children, two girls and one boy, presented with hypothyroidism and precocious sexual development. Serum TSH and PRL were elevated in all cases. In the male patient, pituitary stimulation with TRH produced exaggerated TSH and PRL responses. Elevated serum LH, FSH, estrone, estradiol, and an attenuated gonadotropin response to GnRH were documented in the male patient and in one of the female patients. Serum testosterone was elevated for age in one of the female patients but prepubertal in the male patient. After treatment with L-thyroxine, elevated hormonal levels decreased to normal in one patient who returned for follow-up. Evidence is presented that precocious puberty in juvenile hypothyroidism may be the result of PRL hypersecretion.