Hyperprolactinemia Associated with Hypothalamic Disorder
At a Glance
Hyperprolactinemia is the most common endocrine disorder of the hypothalamic-pituitary unit. In premenopausal women, hyperprolactinemia causes hypogonadism, leading to symptoms of infertility, oligomenorrhea or amenorrhea, and galactorrhea. Hyperprolactinemia is often clinically silent in postmenopausal women who, by definition, are already hypogonadal. In men, hyperprolactinemia causes hypogonadism manifested by decreased libido, impotence, infertility, and, rarely, galactorrhea.
The regulation of prolactin secretion is primarily inhibitory through the action of dopamine released from neurons that extend from the hypothalamus to the anterior pituitary. Hypothalamic thyrotropin-releasing hormone has a stimulatory effect on prolactin release.
Hyperprolactinemia due to disorders of the hypothalamus is usually the result of the diminished synthesis or release of dopamine. These disorders include tumors, arterio-venous malformations, head trauma, irradiation, and inflammatory processes, such as sarcoidosis or central nervous system (CNS) infection.
What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?
The measurement of serum prolactin is necessary to identify hyperprolactinemia. Testing can be performed without regard to time of day, because routine daily activities have little influence on prolactin concentration.
Hypothalamic causes of hyperprolactinemia rarely result in a prolactin concentration that exceeds 150 ng/mL.
Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?
Prolactin concentrations slightly greater than the reference interval should be confirmed by repeat testing on a new blood sample, because prolactin may be influenced by strenuous exercise, emotional or physical stress, or rigorous stimulation of breast tissue.
Several medications are known to cause hyperprolactinemia (see chapter on Anterior Pituitary, Hyperprolactinemia Associated with Drugs). These should be ruled-out as potential causes of hyperprolactinemia prior to investigating organic causes.
Macroprolactin is a complex of prolactin and IgG and is a source of hyperprolactinemia in some individuals. Because of its high molecular mass, macroprolactin has prolonged clearance that can cause an apparent hyperprolactinemia. In the absence of clinical symptoms, hyperprolactinemia due to macroprolactin can cause clinical confusion. It is important to be aware that macroprolactinemia can coexist with true hyperprolactinemia.
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