Thinking About the Pituitary With Amenorrhea, Osteopenia, and Impotence: Prolactinomas

Under what circumstances is a screening prolactin test warranted?

Amenorrhea, infertility, osteopenia, decreased libido, and impotence are common primary care complaints. Typical evaluations effectively address potential problems—estrogen excess or depression as examples—leading to these abnormalities. One organ that may be overlooked in the work-up is the pituitary gland. Forty percent of pituitary tumors produce prolactin. This hormone may be the culprit for all the symptoms and signs mentioned in the opening sentence. A “Top Paper” provides a comprehensive, but clear review of this important pathology.^1,2

WHEN TO SUSPECT A PROLACTINOMA

Women and men have different presenting complaints from prolactinomas. Although both sexes may exhibit neurological signs from larger tumors as well as decreased bone mineral density, premenopausal women usually complain of galactorrhea (80%), infertility, and amenorrhea. Men conversely present with decreased libido and impotence.

Normal levels of prolactin are 20 to 25 µg/L. A single blood test may suffice to suggest prolactin excess in the appropriate clinical situation. In addition to adenomas, drugs (metoclopramide and verapamil as 2 examples), hypothyroidism, chronic renal failure, and pregnancy can lead to elevated levels. If the prolactin level is elevated and other causes are absent (for example, a negative pregnancy test or a normal thyroid-stimulating hormone level), a gadolinium-enhanced MRI scan of the sella is indicated. Functioning adenomas are classified as “micro-” if they are smaller than 10 mm; “macro-” if they are larger.

TREATMENT

The best news about prolactinomas is they are usually amenable to medical therapy. Treatment with either bromocriptine or cabergoline (dopamine antagonists) can normalize prolactin levels and decrease tumor size. Cabergoline is superior in normalizing prolactin, and it is especially effective in reversing hypogonadism. Fertility can be completely restored with dopamine antagonists. Bromocriptine is favored in this regard, since it is less expensive and has been proven safe in pregnancy. If bromocriptine therapy fails, however, cabergoline should be tried before resorting to surgery. Surgery (trans-sphenoidal) is used only when medication therapy fails. The last resort is radiation therapy.

Recently, it has been demonstrated that some patients have remission of disease that continues after withdrawal of either bromocriptine or cabergoline. However, this decision should not be made without consultation. Careful follow-up during the first year after discontinuation is critical.

AN ADDITION TO THE PRIMARY CARE TOOL KIT

I have not consistently considered the contribution of excess prolactin to the common complaints of amenorrhea or impotence. Since diagnosis of prolactin excess is so simple and non-invasive (a single blood test), causes other than adenomas easily uncovered (pregnancy or hypothyroidism, for example), and treatment so beneficial, a screening prolactin measurement will become a more common addition to my primary care tool kit.