# Hyperprolactinaemia > Hyperprolactinaemia for FMGE Medicine: galactorrhoea with amenorrhoea, macroprolactin hook effect, cabergoline therapy and pituitary MRI. - Canonical URL: https://prepelephant.com/topics/fmge/medicine/hyperprolactinaemia-fmge - Exam / course: FMGE · Subject: Medicine - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Hyperprolactinaemia", PrepElephant, https://prepelephant.com/topics/fmge/medicine/hyperprolactinaemia-fmge ## Direct answer Hyperprolactinaemia is an elevated serum prolactin producing galactorrhoea, oligomenorrhoea or amenorrhoea, infertility, low libido and — when a prolactinoma is the cause — mass effects such as headache and bitemporal visual field loss. Causes divide into physiological (pregnancy, lactation, stress), pharmacological (dopamine D2 antagonists — antipsychotics, metoclopramide, domperidone; oestrogens; verapamil), pathological (prolactinoma — microadenoma under 10 mm, macroadenoma 10 mm or more; stalk disease; hypothyroidism; chronic kidney disease) and the assay artefact macroprolactinaemia. After excluding pregnancy, drugs and hypothyroidism, significant elevations warrant pituitary magnetic resonance imaging. Treatment of prolactinoma is dopamine agonist first — cabergoline 0.25-1 mg twice weekly (more effective and better tolerated than bromocriptine), which shrinks most macroadenomas; surgery is reserved for agonist resistance or apoplexy. ## What you must remember - **Symptom split by sex:** women — galactorrhoea, amenorrhoea, infertility, osteoporosis risk from hypo-oestrogenism; men — low libido, erectile dysfunction, gynaecomastia, often late diagnosis with macroadenoma. - **Physiological suppression:** hypothalamic dopamine tonically inhibits prolactin — hence stalk compression raises it modestly (usually under 200 ng/mL) while prolactinomas push it far higher. - **Level-to-lesion logic (a rule of thumb, not a law):** prolactin above 200 ng/mL (about 4000 mIU/L) suggests prolactinoma, with macroadenomas commonly over 500 ng/mL; mild rises with a macroadenoma on imaging suggest stalk effect from a non-functioning adenoma — a distinction that changes management entirely. - **Macroprolactin and the hook effect:** macroprolactin (polymeric, biologically inactive) causes spurious elevation — request polyethylene glycol precipitation when the level and the clinical picture disagree; the high-dose hook effect can artefactually lower prolactin in giant prolactinomas — dilute the sample. - **Work-up order:** pregnancy test, thyroid-stimulating hormone, renal and liver function, drug history; then MRI pituitary with contrast for significant elevations or any visual/neurological sign; formal visual fields for macroadenoma. - **Therapy of choice:** cabergoline 0.25 mg twice weekly titrated (usual range 0.25-1 mg weekly in two doses; up to 2 mg weekly in resistant cases) — shrinkage of macroadenoma, restoration of menses and fertility in most; bromocriptine 2.5-7.5 mg daily preferred when pregnancy is planned because of its longer safety record, then discontinued once pregnancy is confirmed in microprolactinoma. - **Dopamine agonist cautions:** echocardiographic surveillance for valvulopathy at high cumulative cabergoline doses; start low to avoid orthostatic hypotension and nausea; monitor visual fields rather than rushing to surgery when a macroadenoma abuts the chiasm, since medical shrinkage is often dramatic. - **When surgery or radiotherapy:** resistance or intolerance to agonists, apoplexy with deficits, or cerebrospinal fluid leak — trans-sphenoidal surgery in experienced hands. ## Sorting a raised level into its cause A 29-year-old woman presents with six months of amenorrhoea and milky nipple discharge; she takes domperidone for bloating. Step one clears the obvious: pregnancy test negative; thyroid-stimulating hormone mildly raised at 7 mIU/L — hypothyroidism is itself a cause (thyrotropin-releasing hormone stimulates prolactin), so levothyroxine is started and prolactin repeated in eight weeks. It falls but remains 90 ng/mL, and the domperidone is stopped; a further repeat is planned. Only when two reversible causes are removed and the level stays high does imaging enter: MRI shows a 7 mm microadenoma, and cabergoline 0.25 mg twice weekly restores cycles within two months. The contrast case is the man with bitemporal field loss, impotence and a prolactin of 30 ng/mL with a 3 cm sellar mass: the mild elevation marks stalk effect, and the tumour is a non-functioning adenoma or other mass — treating it as a prolactinoma wastes time while a compressive lesion needs surgery. Reading the level against the mass size is the single most consequential judgement in the topic, and the exam constructs exactly this mismatch to test it. ## Where students slip The persistent error is treating every raised prolactin with cabergoline on day one: the marks lie in the sequence — pregnancy, thyroid, drugs, macroprolactin, then MRI. Second, the stalk-effect mismatch (big tumour, small prolactin rise) is the trap of every exam bank; the mirror mismatch (no tumour visible, huge prolactin) suggests giant prolactinoma with hook effect — dilute the assay. Third, in pregnancy planning bromocriptine's safety record is longest, and agonists are stopped on confirmation of pregnancy in microprolactinoma, with monitoring in macroadenoma. Fourth, oestrogen-deficiency bone loss in long-standing untreated amenorrhoea is a viva addition. Fifth, cabergoline valvulopathy surveillance is the modern detail that separates updated candidates from older question banks. ## Frequently asked questions ### What are the commonest causes of hyperprolactinaemia? Pregnancy and lactation, dopamine-antagonist drugs (antipsychotics, metoclopramide, domperidone), hypothyroidism, prolactinoma, and macroprolactinaemia as an assay artefact. ### Which drug is first-line for prolactinoma and at what dose? Cabergoline 0.25-1 mg weekly in two divided doses, superior to bromocriptine in efficacy and tolerance, with shrinkage of macroprolactinomas in most patients. ### What is macroprolactin and why does it matter? Biologically inactive prolactin aggregates causing spuriously high assays with few symptoms; polyethylene glycol precipitation identifies it and avoids unnecessary imaging and treatment. ### Why can a large pituitary tumour cause only mild hyperprolactinaemia? Stalk compression disconnects the pituitary from hypothalamic dopamine, a "stalk effect" (typically under 200 ng/mL), indicating a non-prolactinoma mass rather than a prolactinoma. ### Which dopamine agonist is preferred when pregnancy is planned? Bromocriptine, with the longest pregnancy safety record, discontinued once pregnancy is confirmed in microprolactinoma, with closer monitoring in macroadenoma.