Regression of a pituitary adenoma following levothyroxine therapy of primary hypothyroidism.

Two patients are described who were suffering from primary hypothyroidism and who developed a pituitary microadenoma and macroadenoma with suprasellar extension, respectively, diagnosed by CT scan of the pituitary. Both patients originally presented with amenorrhea and galactorrhea. In addition to low serum T4 and T3 levels and an elevated TSH level, they also had hyperprolactinemia. The TRH test performed in one of the patients showed an exaggerated response of both TSH and PRL to TRH. Correction of hypothyroidism by prolonged (months) treatment with levothyroxine resulted in normalization of thyroid function tests as well as hyperprolactinemia and in regression of the pituitary tumor. It was concluded that primary hypothyroidism was the cause of the pituitary adenoma and the amenorrhea/galactorrhea syndrome. It is recommended that routine thyroid function tests be obtained for patients with hyperprolactinemia. Demonstrable primary hypothyroidism should be corrected for prolonged periods of time by levothyroxine therapy, and CT scanning of the pituitary should be repeated before any other treatment such as bromocriptine or surgery is attempted.