AKT · Endocrine/Pituitary & ADH

Hyperprolactinaemia / prolactinoma

Prolactin excess (prolactinoma; dopamine-antagonist drugs; stalk effect)

Overview

Raised prolactin — from a lactotroph adenoma (prolactinoma, the commonest functioning pituitary tumour), dopamine-antagonist drugs (antipsychotics, metoclopramide), pituitary stalk compression (loss of dopamine inhibition), hypothyroidism or pregnancy. Causes galactorrhoea, hypogonadism (amenorrhoea/low libido) and, with a macroadenoma, mass effects. Treated with a dopamine agonist (NOT surgery first).

Recognise

Women: oligo/amenorrhoea, GALACTORRHOEA, infertility, low libido
Men: erectile dysfunction, low libido, gynaecomastia, infertility (often present late with mass effects)
Macroadenoma: headache, bitemporal hemianopia, hypopituitarism

Red flags

Visual field loss from a macroprolactinoma → urgent
Always exclude drug cause, pregnancy and hypothyroidism before imaging

Differentials & how to tell them apart

Drug-induced (antipsychotics, metoclopramide, antiemetics)dopamine antagonists — the commonest non-tumour cause; mild-moderate elevation

Pituitary stalk compression (non-functioning adenoma)mildly raised prolactin (loss of dopamine inhibition) with a mass — 'disconnection hyperprolactinaemia'

Pregnancy / primary hypothyroidismphysiological / TRH-driven prolactin rise — check βhCG and TSH

Macroprolactinbiologically inactive aggregate — asymptomatic raised prolactin

Investigations

Serum prolactin (very high → prolactinoma; mild → drugs/stalk/macroprolactin). Exclude pregnancy, hypothyroidism (TSH), drugs. MRI pituitary; visual fields; other pituitary axes. Beware the 'hook effect' (falsely low in huge tumours).

Management

Dopamine agonist (cabergoline) — first-line, even for macroadenomas

1Exclude pregnancy, hypothyroidism and drugs first. For a true prolactinoma, start a DOPAMINE AGONIST (cabergoline) — it both normalises prolactin and shrinks the tumour.Gate: Unlike other pituitary tumours, prolactinomas are treated MEDICALLY first (dopamine agonist), not surgically; a mildly raised prolactin with a large tumour is usually stalk compression (a non-functioning adenoma), not a prolactinoma — that distinction changes management
2Surgery/radiotherapy only if intolerant/resistant to dopamine agonists or for apoplexy; treat drug-induced cases by reviewing the drug.

Dopamine agonist (cabergoline/bromocriptine) — first-line even for macroadenomas — shrinks the tumour and normalises prolactin

Stop/switch the offending drug — drug-induced cause (with psychiatry if antipsychotic)

Key points

Galactorrhoea + amenorrhoea + very high prolactin = prolactinoma → cabergoline (medical, tumour-shrinking). The traps: drugs (antipsychotics), pregnancy and hypothyroidism first; and the stalk effect (mildly raised prolactin from a non-prolactin tumour). This is the bridge to the breast/galactorrhoea paraneoplastic chain.

Monitor & prognosis

Prolactin, tumour size on MRI, visual fields.

Excellent — most respond to dopamine agonists.

Source: Endocrine Society; Society for Endocrinology