Endocrinology Made Simple : Prolactinomas

Prolactinomas

Prolactinoma is a benign tumor (adenoma) of the pituitary gland that produces a hormone called prolactin. 

It is the most common type of pituitary tumor.

Epidemiology

Prolactin is a hormone that triggers the breasts to produce milk (lactation).

Prolactinoma is the most common type of pituitary tumor (adenoma). It makes up at least 30% of all pituitary adenomas. 

Almost all pituitary tumors are noncancerous (benign). Prolactinoma may occur as part of an inherited condition called multiple endocrine neoplasia type 1 (MEN 1)

Prolactinomas occur most commonly in people under age 40. They are about five times more common in women than in men, but are rare in children.

At least half of all prolactinomas are very small (less than 1 cm or 3/8 of an inch in diameter). These small tumors are more common in women. 

They stay small and never get larger.

Larger tumors are more common in men. They tend to occur at an older age. 

The tumor can grow to a large size before symptoms appear.

The tumor is often detected at an earlier stage in women than in men.

Medicines that treat low thyroid function (hypothyroidism) and mental illnesses can raise prolactin level. 

This can cause symptoms similar to prolactinoma or an actual prolactinoma.

Symptoms:

Symptoms of prolactinoma are too much prolactin in the blood (hyperprolactinemia) or caused by pressure of the tumor on surrounding tissues.

In women:

Abnormal milk flow from the breast in a woman who is not pregnant or nursing (galactorrhea)

Breast tenderness

Decreased sexual interest

Decreased peripheral vision

Headache

Infertility

Stopping of menstruation not related to menopause, or irregular menstruation

Vision changes

In men:

Decreased sexual interest

Decreased peripheral vision

Enlargement of breast tissue (gynecomastia)

Headache

Impotence

Infertility

Vision changes

Symptoms caused by pressure from a larger tumor may include:

HEADACHE

Lethargy

Nasal drainage

Nausea and vomiting

Problems with the sense of smell

Vision changes, such as double vision, drooping eyelids or visual field loss

There may be no symptoms, especially in men.

Those that are caused by increased prolactin levels are:

Amenorrhea

Galactorrhea (infrequent in men)

Loss of axillary and pubic hair

Hypogonadism, gynecomastia, erectile dysfunction (in males)

Those that are caused by mass effect are:

Bitemporal hemianopsia (due to pressure on optic chiasm)

Vertigo

Nausea, vomiting

Prolactin stimulates the breast to produce milk, and has many other functions such as regulation of 

mood. 

Hence prolactin levels are usually higher during pregnancy and after childbirth.

Each time the milk is dispensed, prolactin levels rise; this process may cycle to maintain milk production.

In males it is responsible for the sexual refractory period after orgasm and excess levels can lead to erectile dysfunction.

Classification

Based on size, a prolactinoma can be classified as a microprolactinoma (<10 mm diameter) or macroprolactinoma (>10 mm diameter).

Microprolactinomas are much more common than macroprolactinomas.

Diagnosis:

Prolactin blood levels

Imaging studies: Brain MRI and CT Scan

In addition to assessing the size of the pituitary tumor, damage to surrounding tissues is assessed, and tests are performed 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.

Management

Medicine is usually successful in treating prolactinoma. Some people have to take these medicines for life. 

Some people can stop taking them, especially if their tumor has disappeared from the MRI. But there is a risk that the tumor may grow and produce prolactin again, especially if it is a large tumor.

The goal of treatment is to return prolactin secretion to normal, reduce tumor size, correct any visual abnormalities, and restore normal pituitary function.

A large prolactinoma can sometimes get larger during pregnancy.

Surgery is done in some cases when symptoms are severe such as sudden worsening of vision.

Radiation is usually only used in patients with prolactinoma that continues to grow or gets worse after 

both medication and surgery. It may be given in the form of:

Conventional radiation

Gamma knife or stereotactic radiosurgery -- a type of radiation therapy that focuses high-powered x-rays on a small area in the brain.

Dopaminergic receptor agonists ( Bromocriptine and Cabergoline) are the first line treatment for prolactinomas including large prolactinomas

With this treatment,the size of tumors decreases within days and patients vision improves even before the decrease in tumor size is appreciated on Brain MRI.

Once treatment with these medications is started,the patients would require close monitoring of his clinical symptoms,

prolactin levels,

visual fields assessments and

MRI of his pituitary gland

Transphenoidal and transcranial surgery is rarely required for patients with prolactinomas.

Even patients with visual field defects and compressive symptoms may respond to treatment with

dopaminergic receptor agonists.

Hypogonadism secondary to hyperprolactinemia is likely to respond to dopaminergic receptor

agoinists and not to treatment with testosterone