The most common cause of galactorrhea is overproduction of the hormone prolactin (hyperprolactinemia) due to a tumor in the pituitary gland.
Hyperprolactinemia can cause galactorrhea, or unexpected milk production, and infertility in both men and women.
The diagnosis is based on measuring the blood levels of the hormone prolactin.
Imaging tests may be done to look for a cause.
When drugs alone do not control prolactin production or shrink the tumor, surgery or sometimes radiation therapy may be done.
(See also Overview of the Pituitary Gland.)
In both sexes, the most common cause of galactorrhea is a prolactin-secreting tumor (prolactinoma) in the pituitary gland. Prolactin is a hormone that stimulates the breasts to produce milk.
Prolactinomas usually are very small when first diagnosed. They tend to be larger in men than in women, possibly because they may come to attention later. Tumors just above the pituitary gland that do not produce prolactin can increase prolactin secretion if they compress the stalk of the pituitary gland. Compressing the stalk can prevent the hormone dopamine from reaching the pituitary gland, where it normally acts to decrease prolactin production.
Overproduction of prolactin and the development of galactorrhea may also be induced by drugs, including phenothiazines, certain drugs given for high blood pressure (especially methyldopa and verapamil), opioids, and birth control pills, and by certain disorders outside the pituitary. Such disorders include an underactive thyroid gland (hypothyroidism), chronic kidney disease, liver disease, and certain lung cancers.
Although unexpected breast milk production may be the only symptom of a prolactinoma, many women also stop menstruating (amenorrhea) or have less frequent menstrual periods. Women with prolactinomas often have low levels of estrogen, which can lead to vaginal dryness, and thus discomfort during sexual intercourse. Some women (and rarely, men) have infertility. About two thirds of men with prolactinomas lose interest in sex (reduced libido) and have erectile dysfunction. Some women also have reduced libido and hirsutism (excessive hair growth on the face and body).
When a prolactinoma is large, it may press on the nerves of the brain that are located just above the pituitary gland, causing the person to have headaches or to become blind in specific visual fields.
The diagnosis is usually suspected in women when menstrual periods are reduced or absent or when breast milk is unexpectedly produced. It is also suspected in men with reduced libido and decreased levels of testosterone in the blood, especially if they are producing breast milk.
It is confirmed by finding a high level of prolactin in the blood.
Computed tomography (CT) or magnetic resonance imaging (MRI) is done to search for a prolactinoma or other tumor near the pituitary. If no tumor is detected and there is no other apparent cause of the high prolactin level (such as a drug), a pituitary tumor is still the most likely cause, particularly in women. In this case, the tumor is probably too small to be seen on the scan.
If a prolactinoma is large on imaging studies, an ophthalmologist tests the person's visual fields for possible effects on vision.
Drugs can be given that mimic dopamine, the chemical in the brain that blocks prolactin production. They include bromocriptine and cabergoline. These drugs are taken by mouth and are effective only as long as they are used. However, studies have shown that about 20 to 25% of people may be able to safely stop taking these drugs after 3 years of therapy.
In most people, these drugs lower prolactin levels enough to restore menstrual periods, stop galactorrhea (in women and men), and increase estrogen levels in women and testosterone levels in men. The drugs are often able to restore fertility. They also usually shrink the tumor and decrease any vision problems.
Surgery is also effective for treating small prolactinomas but is not usually used first because drug treatment is safe, effective, and easy to use.
When a person's prolactin levels are not extraordinarily high and CT or MRI shows only a small prolactinoma or none at all, a doctor may not recommend treatment. This recommendation is probably appropriate in women who are not having problems getting pregnant as a result of the high prolactin level, whose menstrual periods remain regular, and who are not troubled by galactorrhea, and in men whose testosterone level is not low. Low estrogen levels usually accompany amenorrhea and increase the risk of osteoporosis in women. Low testosterone levels increase the risk of osteoporosis in men.
To overcome the effects of low estrogen levels caused by a prolactinoma, estrogen or oral contraceptives that contain estrogen may be given to women with small prolactinomas who do not want to become pregnant. Although estrogen treatment has not been shown to stimulate the growth of small prolactinomas, most experts recommend CT or MRI every year for at least 2 years to be sure the tumor is not enlarging substantially.
Doctors generally treat people who have larger tumors with drugs similar to dopamine( dopamine agonists), for example, bromocriptine or cabergoline, or with surgery. If drugs reduce the prolactin levels and symptoms disappear, surgery may not be necessary. These drugs are generally safe, but formation of excess connective tissue (fibrosis) in heart valves and leakage of blood across the valves have been reported when they were used to treat Parkinson disease in much higher doses than they are used to treat increased prolactin levels. Subsequent studies in people treated with doses used for prolactinomas do not show the same impact on heart valves.
Even when surgery is necessary, dopamine agonists may be given to help shrink the tumor before surgery. They are often given after surgery, because a large prolactin-secreting tumor is unlikely to be cured with surgery. Occasionally, prolactinomas shrink and secrete less prolactin so the dopamine agonists can be stopped without the prolactin level rising again. Being able to stop taking dopamine agonists is more common in people with small tumors and in women after pregnancy.
Radiation therapy is sometimes needed, as for other pituitary tumors, when the tumor does not respond to medical or surgical treatment.