A prolactinoma is a tumor (adenoma) of the pituitary gland that produces the hormone prolactin. It is the most common type of functioning pituitary tumor. Symptoms of prolactinoma are due to abnormally high levels of prolactin in the blood (hyperprolactinemia), or due to pressure of the tumor on surrounding brain tissue and/or the optic nerves. Based on its size, a prolactinoma may be classified as a microprolactinoma (<10mm diameter) or a macroprolactinoma (>10mm diameter).

Signs and symptoms

The most common symptoms at the time of diagnosis often differ between males and females. Females tend to experience more symptoms related directly to abnormally high prolactin levels, such as inappropriate lactation (occurring outside of nursing or recent childbirth) or an absence of menstruation. By contrast, males are more likely to initially present with symptoms of the tumor compressing their brain tissue, such as headaches and vision changes, as well as exhibit fertility issues and hormonal disruptions such as a loss of libido.

The symptoms due to a prolactinoma are broadly divided into those that are caused by increased prolactin levels and those caused directly by the mass itself. Those that are caused by increased prolactin levels are:

  • amenorrhea (lack of menstrual periods)
  • galactorrhea (breastmilk production; less common in males)
  • loss of axillary and pubic hair
  • hypogonadism (reduced function of the gonads)
  • gynecomastia (an increase in breast size in males)
  • erectile dysfunction

Those that are caused directly by the mass itself are:

  • vision changes (visual field deficits, blurred vision, decreased visual acuity)

Causes

Prolactinoma is most frequently a sporadic tumor, occurring in people without any concrete risk factors or family members with similar conditions.

Sporadic cases of prolactinoma which are not related to a mutation of SF3B1 remain poorly understood. However, many studies show a link between estrogen and prolactinoma. This is theorized to be related to why prolactinomas are more common in women than men.

Diagnosis

Prolactinoma is often one of the first diagnoses considered by a physician when a patient presents with symptoms of hyperprolactinemia.

  • Galactorrhea
  • Amenorrhea (in women)
  • Erectile dysfunction (in men)
  • Infertility
  • Diminished libido
  • Weight gain

If these symptoms occur with the simultaneous presence of mass effects, particularly vision problems or severe neurological symptoms such as seizures or coma, aggressive prolactinoma is highly likely.

Medications

Dopamine is the chemical that normally inhibits prolactin secretion, so clinicians may treat prolactinoma with drugs that act like dopamine such as bromocriptine and cabergoline. This type of drug is called a dopamine agonist.

Cabergoline is also associated with side effects such as nausea and dizziness, but these may be less common and less severe than with bromocriptine. However, people with low blood pressure should use caution when starting cabergoline treatment, as the long half-life of the drug (4–7 days) may inadvertently affect their ability to keep their blood pressure within normal limits, creating intense discomfort, dizziness, and even fainting upon standing and walking until the single first dose clears from their system. As with bromocriptine therapy, side effects may be avoided or minimized if treatment is started slowly. If a patient's prolactin level remains normal for 6 months, a doctor may consider stopping treatment. Cabergoline should not be interrupted without consulting a qualified endocrinologist.

Other dopamine agonists that have been used less commonly to suppress prolactin include dihydroergocryptine, ergoloid, lisuride, metergoline, pergolide, quinagolide, and terguride. 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. In non-selective surgical series, this tumor accounts for approximately 25-30% of all pituitary adenomas. Some growth hormone (GH)–producing tumors also co-secrete prolactin. More than 90% of prolactinoma is microprolactinomas, which are much more common than macroprolactinomas.

See also

  • Hypothalamic–pituitary–prolactin axis
  • Hyperprolactinaemia

References

  • Adapted from Prolactinoma. U. S. National Institutes of Health Publication No. 02-3924 June 2002. Public Domain Source