Galactorrhoea

Definition

• Milk production from the breast unrelated to pregnancy or lactation; milk production one year or more after lactation has ended is also considered galactorrhoea.

Occurrence & epidemiology

Epidemiology

• Hyperprolactinaemia is one of the most common problems in clinical endocrinology.
• Prolactinomas, at 57%, are the most frequent subtype of pituitary adenoma, are more common in women and peak in women aged 16 to 48.

Aetiopathogenesis

Aetiology and pathogenesis

• The most common cause is a prolactin-secreting pituitary adenoma (prolactinoma); prolactin is the hormone most frequently produced in excess by pituitary tumours.
• Microprolactinomas measure less than 10 mm and macroprolactinomas more than 10 mm; microadenomas predominate in adult women.
• Non-functioning pituitary masses can compress the pituitary stalk and interrupt the dopamine-mediated suppression of prolactin; prolactin then usually rises no higher than 3 to 4 times normal.
• Other causes include primary hypothyroidism via increased TRH, certain substances such as antipsychotics, metoclopramide, tricyclic antidepressants, opioids and verapamil, renal insufficiency through reduced prolactin clearance, and chest wall lesions such as herpes zoster, scars or trauma.

Clinical features

• The milk is white and fat globules can be seen on microscopy; spontaneous secretion is less common than secretion on manual expression.
• Women with galactorrhoea commonly also have amenorrhoea or oligomenorrhoea, sometimes with signs of oestrogen deficiency such as dyspareunia and reduced libido; other cycle disturbances include infrequent ovulation and corpus luteum dysfunction.
• Space-occupying tumours cause headaches and visual disturbances; this mainly affects men, in whom microadenomas are much less frequent.

Diagnosis

• Diagnosis rests on raised prolactin levels, typically more than 5 times normal in prolactinomas; prolactin levels generally correlate with tumour size.
• Pregnancy is physiologically associated with raised prolactin; primary hypothyroidism is excluded if TSH is not elevated.
• With the extremely high prolactin levels of large prolactinomas, the hook effect can produce artificially low readings, which can be uncovered by repeating the assay at a 1:100 dilution.
• Macroprolactin, mostly complexes of prolactin with IgG or IgA, is considered largely inactive but is detected by immunoassays and can therefore lead to misdiagnosis.
• Contrast-enhanced MRI is the principal method for identifying microadenomas.

Keep learning in the app

Further reading (selection)

1. StatPearls: Galactorrhea (NCBI Bookshelf)
2. MSD Manual Professional: Prolactinoma
3. Hyperprolactinaemia (J Clin Med 2019, PubMed Central)

Cross-references