Merck Manual

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John D. Carmichael

, MD, Keck School of Medicine of the University of Southern California

Reviewed/Revised Apr 2023
Topic Resources

Prolactinomas are noncancerous tumors made up from special cells (lactotrophs) in the pituitary gland. The most common symptom of a prolactinoma is galactorrhea, which is the production of breast milk in men or in women other than during and following pregnancy.

  • Prolactinomas cause the overproduction of the hormone prolactin (hyperprolactinemia) by 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 medication alone does not control prolactin production or shrink the tumor, surgery or sometimes radiation therapy may be done.

In both sexes, the most common cause of galactorrhea is a prolactin-secreting tumor (prolactinoma) in the pituitary gland Overview of the Pituitary Gland The pituitary is a pea-sized gland that is housed within a bony structure (sella turcica) at the base of the brain. The sella turcica protects the pituitary but allows very little room for expansion... read more . Prolactin is a hormone that stimulates the breasts to produce milk.

The Pituitary and Hypothalamus

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.

Other tumors just above the pituitary gland that do not produce prolactin can also 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.

Did You Know?

  • Galactorrhea can occur in both women and men.

Symptoms of Prolactinoma

Although unexpected breast milk production may be the only symptom of a prolactinoma, many women also stop menstruating (amenorrhea Absence of Menstrual Periods Having no menstrual periods is called amenorrhea. Amenorrhea is normal in the following circumstances: Before puberty During pregnancy While breastfeeding read more ) 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 also have reduced libido and hirsutism (excessive hair growth on the face and body). Some women (and rarely, men) have infertility.

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 Visual Pathways and the Consequences of Damage Visual Pathways and the Consequences of Damage .

Diagnosis of Prolactinoma

  • Measurement of blood prolactin level

  • Computed tomography or magnetic resonance imaging

A prolactinomas is usually suspected in women when menstrual periods are reduced or absent or when breast milk is unexpectedly produced (galactorrhea). It is 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 Computed Tomography (CT) In computed tomography (CT), which used to be called computed axial tomography (CAT), an x-ray source and x-ray detector rotate around a person. In modern scanners, the x-ray detector usually... read more Computed Tomography (CT) (CT) or magnetic resonance imaging Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more Magnetic Resonance Imaging (MRI) (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 medication), 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.

Treatment of Prolactinoma

  • Medications to block prolactin production

  • Sometimes surgery or radiation therapy

Medications can be given that mimic dopamine, the chemical in the brain that blocks prolactin production. They include bromocriptine and cabergoline. These medications 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 medications after 3 years of therapy.

In most people, these medications 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 medications 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 treatment with medication 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.

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 and are not receiving dopamine agonist treatment. Although estrogen treatment does not shrink the tumor so 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 medications similar to dopamine (dopamine agonists), for example, bromocriptine or cabergoline, or with surgery. If medications reduce the prolactin levels and symptoms disappear, surgery may not be necessary. These medications 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.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Calan, Calan SR, Covera-HS, Isoptin, Isoptin SR, Verelan, Verelan PM
Cycloset, Parlodel
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