Hyperprolactinemia is a condition characterized by abnormally high concentrations of the hormone prolactin in the blood. While prolactin is known for stimulating milk production in women, it also plays a part in the male endocrine system. In men, prolactin normally maintains a low level and helps regulate reproductive functions, metabolism, and the immune system. An excess of this hormone can disrupt the balance of other hormones, particularly testosterone, leading to health issues.
Manifestations of High Prolactin
The most common signs of hyperprolactinemia stem from its effect of suppressing sex hormone production, resulting in male hypogonadism. This hormonal imbalance frequently leads to pronounced sexual dysfunction, including a noticeable decrease in libido and difficulty achieving or maintaining an erection. High prolactin levels directly impair testosterone production, causing these symptoms.
Infertility is another frequent consequence, as the hormone imbalance impairs testicular function, leading to reduced sperm production and lower sperm counts. Physical changes due to the shift in hormone levels include gynecomastia (the development of excess breast tissue). A less common but specific sign is galactorrhea, the spontaneous production of a milky discharge from the nipples.
Systemic signs related to prolonged low testosterone include loss of body hair and muscle mass, alongside reduced bone density, which may increase fracture risk. If the cause is a large pituitary tumor (macroadenoma), the tumor can press on surrounding brain structures. This pressure can manifest as persistent headaches or visual field disturbances, typically affecting peripheral vision.
Common Causes and Underlying Conditions
High prolactin levels generally stem from three categories: tumors, medications, and systemic diseases. The most frequent pathological cause is a prolactinoma, a noncancerous growth (adenoma) of the pituitary gland that actively secretes prolactin. These tumors are classified by size: microadenomas measure less than 10 millimeters, and macroadenomas are larger.
Many hyperprolactinemia cases are drug-induced, resulting from medications that interfere with dopamine signaling. Dopamine naturally inhibits prolactin release, so any drug blocking its action can cause levels to rise. Common culprits include certain antipsychotic medications (such as risperidone), some antidepressants, opioids, and specific blood pressure medications.
Systemic health problems can also disrupt the body’s ability to regulate or clear prolactin. Untreated primary hypothyroidism (an underactive thyroid gland) can cause an increase in prolactin due to a compensatory mechanism. Chronic kidney failure and liver disease can diminish the body’s metabolic clearance of the hormone, contributing to its accumulation. Other non-tumorous causes include damage to the pituitary stalk, which carries dopamine from the hypothalamus to the pituitary gland.
Confirmation and Measurement
Identifying hyperprolactinemia begins with a blood test to measure the serum prolactin level. For adult men, a normal concentration is typically below 20 nanograms per milliliter, though this range varies between laboratories. If the initial result is mildly elevated, a repeat test is often performed to rule out a transient rise due to stress, strenuous exercise, or recent nipple stimulation.
Testing for macroprolactinemia is important; this is a condition where prolactin circulates in a large, biologically inactive complex. This form does not usually cause symptoms, but it can artificially inflate the measurement, potentially leading to unnecessary investigation. If the prolactin level is persistently high (especially above 200 nanograms per milliliter) or if symptoms are present, magnetic resonance imaging (MRI) of the brain is typically ordered. MRI is the preferred imaging method to visualize the pituitary gland and determine if a prolactinoma or another mass is the underlying cause.
Treatment and Management Strategies
Management of hyperprolactinemia is determined by the underlying cause and symptom severity. For prolactinomas, medical therapy with dopamine agonists is the established first-line treatment. These medications mimic dopamine, effectively suppressing prolactin secretion and often shrinking the tumor size.
Cabergoline is often the preferred dopamine agonist due to its superior efficacy, better tolerability, and convenient twice-weekly dosing. Bromocriptine is an effective alternative, typically used if cabergoline is not tolerated or available. When high prolactin is a medication side effect, management involves consulting a healthcare provider to adjust the dosage or switch to an alternative drug.
If a systemic condition like hypothyroidism is the root cause, treating the primary disease with thyroid hormone replacement usually normalizes prolactin levels. Surgical removal of the tumor, via a transsphenoidal approach through the nose, is reserved for patients who cannot tolerate medical therapy, whose tumors do not respond to dopamine agonists, or whose large tumors cause acute visual field loss. Radiation therapy is a third-line option when both medical and surgical treatments have failed.