Failure of nomifensine administration to discriminate between tumorous and nontumorous hyperprolactinemia

It has recently been claimed that the PRL-lowering response to nomifensine administration (200 mg, orally) reliably discriminates patients with PRL-secreting tumors from those with so-called functional hyperprolactinemia. In the present study, this test was performed in 15 healthy controls, 7 hyperprolactinemic subjects without evidence of pituitary tumor, and 16 patients with prolactinoma. A decrease of serum PRL to below 65% of basal levels, which seemed to be the cut-off point in the previous study, was obtained in 11 subjects of the first group, in 4 subjects of the second group, and in 4 subjects of the third group. The decrease of mean serum PRL concentration after nomifensine was only significant in the first and second groups. Analysis of variance showed a significant difference in the PRL inhibition by nomifensine between the tumor group and the two groups without evidence of pituitary adenoma. Nevertheless, this study shows that the nomifensine test is unable to discriminate in the individual patient the tumorous or nontumorous origin of excessive PRL secretion.