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Abstract
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.