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What Is a Prolactinoma? |
A prolactinoma is a benign tumor
of the pituitary gland that produces a hormone called prolactin.
It is the most common type of pituitary tumor. Symptoms of
prolactinoma are caused by too much prolactin in the blood
(hyperprolactinemia) or by pressure of the tumor on surrounding
tissues.
Prolactin stimulates the breast to produce milk during pregnancy. After delivery of the baby, a mother's prolactin levels fall unless she breast feeds her infant. Each time the baby nurses, prolactin levels rise to maintain milk production. |
What Is the Pituitary Gland? |
The pituitary gland, sometimes called the master gland, plays a
critical role in regulating growth and development, metabolism,
and reproduction. It produces prolactin and a variety of other
key hormones. These include growth hormone, which regulates
growth; ACTH (corticotropin), which stimulates the adrenal
glands to produce cortisol; thyrotropin, which signals the
thyroid gland to produce thyroid hormone; and luteinizing
hormone and follicle-stimulating hormone, which regulate
ovulation and estrogen and
progesterone production in women, and sperm formation and
testosterone production in men.
The pituitary gland sits in the middle of the head in a bony box called the sella turcica. The eye nerves sit directly above the pituitary gland. Enlargement of the gland can cause local symptoms such as headaches or visual disturbances. Pituitary tumors may also impair production of one or more pituitary hormones, causing reduced pituitary function (hypopituitarism). |
How Common Is Prolactinoma? |
Autopsy studies indicate that 25 percent of the U.S. population
have small pituitary tumors. Forty percent of these pituitary
tumors produce prolactin, but most are not considered clinically
significant. Clinically significant pituitary tumors affect the
health of approximately 14 out of 100,000 people.
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What Causes Prolactinoma? |
Although research continues to unravel the mysteries of
disordered cell growth, the cause of pituitary tumors remains
unknown. Most pituitary tumors are sporadic--they are not
genetically passed from parents to offspring.
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What Are the Symptoms? |
In women, high blood levels of prolactin often cause
infertility and changes in menstruation. In some women, periods
may disappear altogether. In others, periods may become
irregular or menstrual flow may change. Women who are not
pregnant or nursing may begin producing breast milk. Some women
may experience a loss of libido (interest in sex). Intercourse
may become painful because of vaginal dryness.
In men, the most common symptom of prolactinoma is impotence. Because men have no reliable indicator such as menstruation to signal a problem, many men delay going to the doctor until they have headaches or eye problems caused by the enlarged pituitary pressing against nearby eye nerves. They may not recognize a gradual loss of sexual function or libido. Only after treatment do some men realize they had a problem with sexual function. |
What Else Causes Prolactin To Rise? |
In some people, high blood levels of prolactin can be traced to
causes other than a pituitary tumor.
Prescription Drugs. Prolactin secretion in the pituitary is normally suppressed by the brain chemical, dopamine. Drugs that block the effects of dopamine at the pituitary or deplete dopamine stores in the brain may cause the pituitary to secrete prolactin. These drugs include the major tranquilizers trifluoperazine (Stelazine) and haloperidol (Haldol); metoclopramide (Reglan), used to treat gastroesophageal reflux and the nausea caused by certain cancer drugs; and less often, alpha methyldopa and reserpine, used to control hypertension.
Other Pituitary Tumors. Other tumors arising in or near the pituitary--such as those that cause acromegaly or Cushing's syndrome--may block the flow of dopamine from the brain to the prolactin-secreting cells.
Hypothyroidism. Increased prolactin levels are often seen in people with hypothyroidism, and doctors routinely test people with hyperprolactinemia for hypothyroidism.
Breast Stimulation also can cause a modest increase in the amount of prolactin in the blood. |
How is Prolactinoma Diagnosed? |
A doctor will test for prolactin blood levels in women with
unexplained milk secretion (galactorrhea) or irregular menses or
infertility, and in men with impaired sexual function and, in
rare cases, milk secretion. If prolactin is high, a doctor will
test thyroid function and ask first about other conditions and
medications known to raise prolactin secretion. The doctor will
also request a magnetic resonance imaging (MRI), which is the
most sensitive test for detecting pituitary tumors and
determining their size. MRI scans may be repeated periodically
to assess tumor progression and the effects of therapy.
Computer Tomography (CT scan) also gives an image of the
pituitary, but it is less sensitive than the MRI.
In addition to assessing the size of the pituitary tumor, doctors also look for damage to surrounding tissues, and perform tests to assess whether production of other pituitary hormones is normal. Depending on the size of the tumor, the doctor may request an eye exam with measurement of visual fields. |
How Is Prolactinoma Treated? |
Medical Treatment The goal of treatment is to return prolactin secretion to normal, reduce tumor size, correct any visual abnormalities, and restore normal pituitary function. In the case of very large tumors, only partial achievement of this goal may be possible. Because dopamine is the chemical that normally inhibits prolactin secretion, doctors may treat prolactinoma with bromocriptine or cabergoline, drugs that act like dopamine. This type of drug is called a dopamine agonist. These drugs shrink the tumor and return prolactin levels to normal in approximately 80 percent of patients. Both have been approved by the Food and Drug Administration for the treatment of hyperprolactinemia. Bromocriptine is the only dopamine agonist approved for the treatment of infertility. Another dopamine agonist, pergolide, is available in the U.S., but is not approved for treating conditions that cause high blood levels of prolactin.
Bromocriptine is associated with side effects such as nausea and dizziness. To avoid these side effects, it is important for bromocriptine treatment to start slowly. An example of a typical approach used by an experienced endocrinologist follows:
Begin by taking a quarter of a 2.5 milligram tablet of bromocriptine with a snack at bedtime. After 3 days, increase the dose to a quarter of a tablet with breakfast and a quarter at bedtime. After 3 more days, take half a tablet twice a day, and 3 days later, one tablet at night and half with breakfast. Finally, the dose is increased to one tablet twice a day. If prolactin is still high, add half a tablet with lunch. If the medication is well tolerated, increase the dose to a full tablet. If side effects develop with a higher dose, return to the previous dosage. With time, side effects disappear while the drug continues to lower prolactin.
Bromocriptine treatment should not be interrupted without consulting a qualified endocrinologist. Prolactin levels often rise again in most people when the drug is discontinued. In some, however, prolactin levels remain normal, so the doctor may suggest reducing or discontinuing treatment every two years on a trial basis.
Cabergoline is also associated with side effects such as nausea
and dizziness, but these may be less common and less severe than
with bromocriptine. As with bromocriptine therapy, side effects
may be avoided if treatment is started slowly. An example of a
typical approach used by an experienced endocrinologist
follows:
Cabergoline should not be interrupted without consulting a qualified endocrinologist.
Surgery
The results of surgery depend a great deal on tumor size and prolactin level as well as the skill and experience of the neurosurgeon. The higher the prolactin level, the lower the chance of normalizing serum prolactin. In the best medical centers, surgery corrects prolactin levels in 80 percent of patients with a serum prolactin less than 250 ng/ml. Even in patients with large tumors that cannot be completely removed, drug therapy may be able to return serum prolactin to the normal range after surgery. Depending on the size of the tumor and how much of it is removed, studies show that 20 to 50 percent will recur, usually within five years.
How do I choose a skilled neurosurgeon? |
How Does Prolactinoma Effect Pregnancy and Oral Contraceptives? |
If a woman has a small prolactinoma, there is no reason that
she cannot conceive and have a normal pregnancy after successful
medical therapy. The pituitary enlarges and prolactin
production increases during normal pregnancy in women without
pituitary disorders. Women with prolactin-secreting tumors may
experience further pituitary enlargement and must be closely
monitored during pregnancy. However, damage to the pituitary or
eye nerves occurs in less than one percent of pregnant women
with prolactinoma. In women with large tumors, the risk of
damage to the pituitary or eye nerves is greater, and some
doctors consider it as high as 25 percent. If a woman has
completed a successful pregnancy, the chances of her completing
further successful pregnancies is extremely high.
A woman with a prolactinoma should discuss her plans to conceive
with her physician, so she can be carefully evaluated prior to
becoming pregnant. This evaluation will include a magnetic
resonance imaging (MRI) scan to assess the size of the tumor and
an eye examination with measurement of visual fields. As soon
as a patient is pregnant, her doctor will usually advise that
she stop taking bromocriptine or cabergoline, the common
treatments for prolactinoma. Most endocrinologists see patients
every two months throughout the pregnancy. The patient should
consult her endocrinologist promptly if she develops
symptoms--particularly headaches, vi" VALIGN="TOP">
Pituitary Tumor Network Association
This e-text is not copyrighted. NIDDK encourages users to duplicate and distribute as many copies as needed. Printed single copies may be obtained from the Office of Communications and Public Liaison, 31 CENTER DRIVE, MSC 2560, Bethesda, Maryland 20892-2560. |
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NIH Publication No. 95-3924 February 1995 e-text posted: 20 February 1998 |