In women, high blood levels of prolactin may cause changes in menstruation and affect fertility. 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.

In men, the most common symptom of prolactinoma is erectile dysfunction due to low testosterone levels.. 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 visual problems caused by the large pituitary tumor pressing against the nearby optic chiasm or optic nerves.

Although research continues to unravel the mysteries of disordered cell growth, the cause of pituitary tumors remains unknown. Most pituitary tumors are not genetically passed from parents to offspring.

A common cause of an elevated prolactin level is normal pregnancy.

In some people, high blood levels of prolactin can be traced to causes other than a pituitary tumor.

What other conditions cause prolactin levels to rise?

• 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 psychiatric medications, such as haloperidol (Haldol) and risperidone (Risperdal), and metoclopramide (Reglan), used to treat gastroesophageal reflux and nausea.

• Other Pituitary Tumors -- Other tumors arising in or near the pituitary, such as nonfunctioning pituitary tumors, may block the inhibitory effects of dopamine from the brain. Other tumors, particularly growth hormone secreting tumors (those that cause acromegaly), may co-secrete prolactin.

• Hypothyroidism. A mild increase in prolactin levels can be seen in people with hypothyroidism, and doctors routinely test people with hyperprolactinemia for hypothyroidism.

• Kidney dysfunction can also cause an accumulation of prolactin in the blood.

• Breast stimulation also can cause a modest increase in the amount of prolactin in the blood.

What effect do prolactinomas have on pregnancy and nursing?

• If a woman has a small prolactinoma, there is no reason that she cannot conceive and have a normal pregnancy with 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 vision occurs in less than one percent of pregnant women with prolactinomas. In women with large tumors, the risk of damage to the pituitary or vision is greater.
  

• 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 proximity to the visual system, and an eye examination with assessment of visual fields. For patients taking cabergoline, a switch to bromocriptine is generally advised because of the much greater amount of safety data in pregnancy that is available. As soon as a patient is pregnant, her doctor will usually advise that she stop taking bromocriptine. The patient should consult her endocrinologist promptly if she develops symptoms, particularly headaches, or visual changes. An MRI during pregnancy but without contrast may sometimes be indicated in such cases, and bromocriptine treatment can be restarted if necessary. Most patients with prolactinomas can nurse successfully.

Is osteoporosis a risk in women with high prolactin levels?

• Women whose ovaries produce inadequate estrogen are at increased risk for osteoporosis. Hyperprolactinemia can cause reduced estrogen production. Although estrogen production may be restored after treatment for hyperprolactinemia, even a year or two without estrogen can compromise bone density. Women may want to have bone density measurements to assess the effect of estrogen deficiency on bone density.

A doctor will test for prolactin blood levels in anyone with unexplained milk secretion (galactorrhea), women with irregular or absent periods or infertility, and men with erectile dysfunction. If the prolactin level is high in a woman of reproductive age, pregnancy should be ruled out. Thyroid function tests and kidney function tests should be measured and the patient should be asked about other conditions and medications known to raise prolactin levels. If indicated, the next step is often an MRI, which is the most sensitive test for detecting pituitary tumors and determining their size. If a pituitary tumor is seen, an IGF-1 level is often measured to rule out a growth hormone-secreting tumor.

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 assessment of visual fields.

Most prolactinomas can be treated with medication. The goal of treatment is to reduce prolactin levels, stabilize or reduce tumor size, correct any visual abnormalities. and restore normal pituitary function.

There are two medications in common use for the treatment of prolactinomas -- cabergoline and bromocriptine. Both are dopamine agonists, which inhibit the secretion of prolactin and shrink the tumor in most cases. Cabergoline is the more potent of the two medications, has few side effects, and can usually be taken once a week. However, data in patients with Parkinson's Disease who have taken much larger doses of cabergoline than the typical prolactinoma patient has raised concern about possible heart valve effects, and safety during pregnancy has not been established. Therefore, bromocriptine is used in many patients, including those seeking pregnancy. The most common side effect is nausea, which can often be mitigated by increasing the dose slowly, taking the medication before bed with a snack and/or by vaginal administration. Rare patients may experience psychologic effects from the medication, including anger, impulsivity and compulsive behavior. In addition, patients who are at risk for psychosis should not take these medications, which can worsen these psychiatric diseases. In most cases, these medications have to be taken indefinitely, but occasionally patients may experience short-term or even lasting remissions after taking the medications for at least 2-3 years.

Surgery

• Surgery may be considered if medical therapy cannot be tolerated or if it fails to reduce prolactin levels, restore normal vision, reproductive function and pituitary function, and adequately reduce or control tumor size.
  

• The results of surgery depend a great deal on tumor size and prolactin level as well as the skill and experience of the neurosurgeon. Even large and invasive tumors may sometimes respond dramatically to medical treatment.