Patients with primary hypothyroidism presenting as prolactinomas.

Hyperprolactinemia can occur in patients with primary hypothyroidism. Two women with hypothyroidism who had elevated serum prolactin levels, galactorrhea, amenorrhea, and pituitary computed tomographic scans that demonstrated the presence of "pituitary tumors" were recently evaluated. It was believed that they had prolactinomas, and they were referred for possible surgery. An elevated serum thyroid-stimulating hormone level, however, suggested that they had primary hypothyroidism and probably pituitary enlargement secondary to pituitary hyperplasia. Detailed evaluation of thyroid-stimulating hormone and prolactin secretion was performed. These studies revealed several abnormalities in dopamine-prolactin interactions; however, the primary event responsible for the hyperprolactinemia is unclear. These women were given thyroxine therapy, and subsequent radiologic and endocrine studies documented resolution of their "pseudotumors" and normalization of the serum thyroxine and prolactin levels. Hence, thyroid-stimulating hormone levels should be measured in all patients presenting with a suspected prolactinoma so that any hypothyroidism that is noted is not presumed to be due to secondary hypothyroidism from tumor involvement of the pituitary.