Prolactinomas are the most common hormonally active pituitary tumors. They account for 40%-60% of all pituitary tumors. These pituitary adenomas have an unregulated and continuous secretion of the hormone prolactin. The high levels of prolactin (hyperprolactinemia) have a different effect on women and men.
In pre-menopausal women, the elevated prolactin causes suppression of LH and FSH, then estrogen and progesterone levels, resulting in irregular or complete cessation of menses (amenorrhea). Hyperprolactinemia can also cause breast enlargement and milk production or discharge (galactorrhea). The low levels of estrogen mimic menopause and can result in diminished libido, osteoporosis, and vaginal dryness. Even mild elevations in prolactin have been associated with infertility.
Because the symptoms of amenorrhea and galactorrhea occur early in the development of these tumors, prolactinomas are often diagnosed when the tumor is small. In men and post-menopausal women, the hormonal symptoms are less pronounced. Hyperprolactinemia in men can cause suppression of testosterone release, resulting in diminished libido. Even in men, breast enlargement (gynecomastia) and breast discharge can occur. High levels of prolactin can also result in weight gain and neuropsychological disturbances. The size of the tumor correlates with the amount of prolactin secreted. Larger tumors can cause mass effects by compression of local structures.
For microprolactinomas, treatment options include surgical resection of the tumor or medical therapy. Surgical resection by an experienced neurosurgeon is highly successful. Medical therapy with agents such as bromocriptine or cabergoline is very effective for controlling both hyperprolactinemia and growth of the prolactinoma, but does require life-long treatment.
Dopamine agonists inhibit production and secretion of prolactin from lactotroph adenomas and results in the shrinkage of the cell size and a decrease in secretory vesicles, which results in shrinkage of the overall tumor size. Dopamine agonists also prevent tumor cells from replicating, causing the tumor to stop growing. An appropriate discussion with both an endocrinologist and a neurosurgeon specialized in this disorder is needed to determine the most appropriate therapy.
For macroprolactinomas, surgical resection is less effective due to the invasive nature of the tumor. Surgery is usually reserved for patients planning a pregnancy, patients with visual deterioration not reversed by dopamine agonists, or those who are intolerant of medical therapy.
Treatment for the increased levels of prolactin depends on the cause. Normalization of prolactin levels results in immediate restoration of menstrual function and fertility in women and libido and potency in men, assuming the residual normal gland remains functional. In cases of drug-induced hyperprolactinemia, cessation of the offending drug is often sufficient to return prolactin levels to normal. In patients with psychosis, selection of anti-psychotics that do not induce hyperprolactinemia should be instituted. For hypothyroid-related hyperprolactinemia, treatment of the hypothyroidism with thyroxine will result in normalization of prolactin levels in the body.