Comparison of the responses in the nomifensine test with hyperprolactinemia due to prolactin-secreting pituitary tumors and nonprolactin-secreting hypothalamic tumors.

It has recently been proposed that nomifensine (Nom) administration discriminates those patients with PRL-secreting pituitary tumors from those who have hyperprolactinemia due to other causes. In the present study, this test was performed on 12 presumed functional hyperprolactinemic subjects, 9 patients with surgically proved PRL-secreting pituitary adenoma (6 microadenoma and 3 macroadenoma), and 7 patients with surgically proved non-PRL-secreting hypothalamic tumors (3 craniopharyngioma, 3 suprasellar germinoma, and 1 suprasellar ependymoma). The Nom test suppressed the plasma PRL level to below 60% of the basal level in all 12 women with presumed functional hyperprolactinemia, but did not alter plasma PRL levels in the patients with PRL-secreting pituitary adenoma or hypothalamic tumor. This evidence confirms that the test is, at least in part, able to discriminate those individuals with PRL-secreting pituitary adenoma from those without, regardless of the size of the tumor. However, the test is not capable of distinguishing between hyperprolactinemia due to PRL-secreting pituitary tumors and that due to non-PRL-secreting hypothalamic tumors. A lack of response to Nom is not necessarily due to the presence of a PRL-secreting tumor, and may be related to dysfunction to the hypothalamic-pituitary system.