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 tissues. Based on size, a prolactinoma can be classified as a microprolactinoma (<10 mm diameter) or a macroprolactinoma (>10 mm diameter).
Signs and symptoms
The symptoms due to a prolactinoma are broadly divided into those that are caused by increased prolactin levels or mass effect.
Those that are caused by increased prolactin levels are: Amenorrhea (disappearance of ovulation periods) Galactorrhea (Milk production; infrequent in men) Loss of axillary and pubic hair Hypogonadism (Reduced function of the gonads.) Gynecomastia (an increase in male breast size) Erectile dysfunction (in males)
Those that are caused by mass effect are: Headaches Vision Changes-visual field deficits, blurred vision, decreased visual acuity Cranial nerve palsies-especially with invasive tumors or with pituitary apoplexy Seizures, Hydrocephalus, Unilateral exophthalmos are rare presentations Hypopituitarism Pituitary apoplexy is a medical emergency because of spontaneous hemorrhage into the pituitary tumor and presents with severe headaches, vision changes, and acute panhypopituitarism.
Causes
The cause of pituitary tumors remains unknown. Though most pituitary tumors are sporadic, some genetic syndromes include increased risk for pituitary adenomas including Multiple endocrine neoplasia type 1 (caused by a mutation in the MEN1 gene) and Familial isolated pituitary adenoma (FIPA).
The majority of moderately raised prolactin levels (up to 5000 mIU/L) are not due to microprolactinomas but other causes. The effects of some prescription drugs are the most common. Other causes are other pituitary tumours and normal pregnancy and breastfeeding. This is discussed more under hyperprolactinaemia.
The xenoestrogenic chemical Bisphenol-A has been shown to lead to hyperprolactinaemia and growth of prolactin-producing pituitary cells. The increasing and prolonged exposure of Bisphenol-A from childhood on, may contribute to the growth of a Prolactinoma.
Diagnosis
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. Computed 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.
Treatments
The goal of treatment is to return prolactin secretion to normal, reduce tumor size, correct any visual abnormalities, and restore normal pituitary function. As mentioned above, the impact of stress should be ruled out before the diagnosis of prolactinoma is given. Exercise can significantly reduce stress and, thereby, prolactin levels. In the case of very large tumors, only partial reduction of the prolactin levels may be possible.
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. These drugs shrink the tumor and return prolactin levels to normal in approximately 80% of patients. Both bromocriptine and cabergoline have been approved by the Food and Drug Administration for the treatment of hyperprolactinemia. Bromocriptine is associated with side-effects such as nausea and dizziness and hypotension in patients with already low blood pressure readings. To avoid these side-effects, it is important for bromocriptine treatment to start slowly.