endocrine and metabolic disorders
Prolactinoma
Etiology of Prolactinoma
Prolactinomas are noncancerous tumors composed of lactotrophs, which are prolactin-secreting adenomas. Prolactin is produced in cells called lactotrophs that constitute about 30% of the cells of the anterior pituitary. In humans, the major function of prolactin is stimulating milk production. Prolactin is the hormone most frequently produced in excess by pituitary tumors. In contrast to other anterior pituitary hormones, prolactin is regulated primarily by suppression bydopamine, and not by negative feedback from peripheral hormones. Galactorrhea is generally due to a prolactin-secreting pituitary adenoma (prolactinoma) but may result from any cause of hyperprolactinemia (see table). Most tumors in women are microadenomas (<10 mm in diameter), but a small percentage are macroadenomas (>10 mm) when diagnosed. The frequency of microadenomas is much lower in men, perhaps because of later recognition; however, for reasons that are unclear, prolactin secreting adenomas have more aggressive growth and cause more severe symptoms of mass effect (eg headaches or visual complaints) and fewer symptoms related to hormone deficiency in men. Nonfunctioning pituitary mass lesions also can increase prolactin levels by compressing the pituitary stalk and thus interrupting the action ofdopamine, which normally suppresses prolactin secretion. ), and opioids. Primary Hypothyroidism can cause hyperprolactinemia and galactorrhea because increased levels of thyroid-releasing hormone increase secretion of prolactin as well as thyroid-stimulating hormone (TSH). Prolactin levels may rise in circulation as a consequence of renal insufficiency due to impaired renal clearance of prolactin. Nipple stimulation and pregnancy are physiologic causes of increased prolactin secretion. Hyperprolactinemia may be associated with hypogonadotropism and hypogonadism probably through inhibition of gonadotrophin-releasing hormone (GnRH) release or action on the pituitary gonadotropes (see table Cause Example Physiologic Early infancy (up to 3 months) Food ingestion Hypoglycemia None Nipple stimulation in women Pregnancy Postpartum period Sexual intercourse in some women Sleep Stress Hypothalamic disorders Head trauma Hypothalamic tumors Idiopathic galactorrhea (presumed abnormality indopaminesecretion) Nontumerous hypothalamic infiltration: Sarcoidosis , Postencephalitis Pituitary disorders Empty sella syndrome None Prolactin-secreting pituitary tumors Surgical pituitary stalk section and other stalk lesions Tumors causing pituitary stalk compression Other endocrine disorders Gigantism and Acromegaly None Cushing Syndrome None Primary Hypothyroidism None Disorders of other systems Chronic Kidney Disease None Ectopic production of prolactin: Bronchogenic carcinoma (not squamous cell; mostly small cell undifferentiated) Hypernephroma Liver disease Chest wall lesions Herpes Zoster None Surgical scars Trauma Tumors Pharmacologic Antihypertensive medications: Alpha-methyldopa,atenolol,clonidine,labetalol, reserpine,verapamil H2-antagonists Oral contraceptives andestrogens Opioids Psychoactive medications, eg, benzamides (metoclopramide, sulpiride), butyrphenones (haloperidol), phenothiazines, tricyclic and some other antidepressants Thyrotropin-releasing hormone Data from Rebar RW: Practical evaluation of hormonal status. InReproductive Endocrinology: Physiology, Pathophysiology and Clinical Management, edited by SSC Yen and RB Jaffe. Philadelphia, WB Saunders Company, 1978, p. 493. 