Prolactinoma
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Prolactinoma is a benign adenoma of the pituitary gland causing hyperprolactinaemia. It is the most common functioning pituitary tumour (40%). Elevated Prolactin inhibits GnRH release, causing Hypogonadism (Low FSH/LH, Low Testosterone/Oestrogen).
Clinical Scenario: The Man with Low Libido
A 45-year-old man presents with a 2-year history of erectile dysfunction and loss of libido. He mentions he has bumped his car recently while parking. Serum Prolactin is 25,000 mU/L.
Key Teaching Points
- **Diagnosis**: **Macroprolactinoma**.
- **Symptoms**: Men present late because sexual dysfunction is often dismissed. The tumour grows large enough to compress the optic chiasm (Visual Field Defect).
- **Levels**: A level of >5,000 mU/L confirms a secreting tumour (unlike the 'Stalk Effect' which is usually <2,000).
- **Treatment**: **Cabergoline** (Medical therapy is first line, even for large tumours).
Image Integration Plan
| Image Type | Source | Status |
|---|---|---|
| Management Algorithm | AI-generated | PENDING |
| MRI (Microadenoma) | Web Source | PENDING |
| MRI (Macroadenoma) | Web Source | PENDING |
| Visual Fields (Bitemporal) | Web Source | PENDING |
[!NOTE] Image Generation Status: Diagrams illustrating the Dopamine inhibition pathway are queued.
Drug induced vs Stalk Effect vs Prolactinoma
| Cause | Mechanism | Prolactin Level (mU/L) |
|---|---|---|
| Drug Induced | Dopamine Antagonists (e.g. Haloperidol, Metoclopramide) remove inhibition. | 500 - 3,000 |
| Stalk Effect | Non-functioning mass compresses stalk, blocking Dopamine flow. | 500 - 2,000 |
| Microprolactinoma | Secreting Tumour < 10mm. | 2,000 - 5,000 |
| Macroprolactinoma | Secreting Tumour > 10mm. | > 5,000 (Often >0,000) |
- Prevalence: Most common pituitary tumour.
- Sex:
- Women: Present early (Microadenomas) due to amenorrhoea.
- Men: Present late (Macroadenomas) due to mass effect.
- Normal Physiology: Prolactin secretion is tonically inhibited by Dopamine (Prolactin Inhibiting Factor) from the hypothalamus.
- Tumour: Adenoma cells secrete Prolactin autonomously.
- HPA Axis: High Prolactin -> Inhibits GnRH pulsatility -> Hypogonadotropic Hypogonadism.
Women (Premenopausal)
Men
Mass Effect (Macroadenomas)
- Visual Fields: Confrontation testing (Red pin).
- Cranial Nerves: III, IV, VI palsy (Cavernous sinus invasion).
- Breast: Check for galactorrhoea (expressible).
- Serum Prolactin:
- Ideally fasting, non-stressed (stress raises PRL).
- Macroprolactin Screen: Essential to exclude "Macroprolactin" (Prolactin bound to IgG, biologically inactive but detected by assay).
- MRI Pituitary (with Gadolinium):
- Definitive imaging.
- Anterior Pituitary Profile:
- Check IGF-1, TSH, Cortisol, LH/FSH, Testosterone/Oestradiol (to exclude co-secretion or hypopituitarism).
- Visual Fields: Formal perimetry (Humphrey).
Unlike other pituitary tumours, Medical Therapy is FIRST LINE.
A. Medical Therapy (Dopamine Agonists)
- Cabergoline:
- Drug of choice (weekly dosing, fewer side effects).
- High affinity D2 receptor agonist.
- Effect: rapid fall in PRL and Tumour Shrinkage (even massive macroadenomas melt away).
- Bromocriptine: Older, daily dosing, more nausea. Used in pregnancy.
- Side Effects: Nausea, Postural Hypotension.
- Impulse Control Disorders: Gambling, Hypersexuality (warn patients/partners!).
- Fibrosis: Cardiac valve fibrosis seen in high doses (Parkinson's) but rare in endocrine doses. Echocardiogram if high dose.
B. Surgery (Trans-sphenoidal)
- Indications:
- Resistance/Intolerance to medical therapy.
- Acute visual loss not responding to drugs.
- Pituitary Apoplexy (Haemorrhage).
- Cerebrospinal Fluid (CSF) Rhinorrhoea (drug shrinks tumour, exposing a hole in the skull base).
C. Pregnancy
- Microprolactinoma: Stop Cabergoline when pregnancy confirmed. (Risk of growth is low <2%).
- Macroprolactinoma: Continue Bromocriptine. Monitor visual fields (Risk of growth 20-30%).
- Osteoporosis: Due to long-standing hypogonadism.
- Infertility.
- Pituitary Apoplexy: Infarction/Haemorrhage of tumour. Medical Emergency.
- Excellent response to Dopamine Agonists (>90%).
- Can often trial withdrawal of drug after 2 years if PRL normal and tumour vanished.
- Endocrine Society Guidelines: Diagnosis and Treatment of Hyperprolactinemia.
- Pituitary Society Guidelines.
What is a Prolactinoma? It is a small, benign growth (not cancer) on the pituitary gland, which is the master gland behind your eyes. The growth produces too much of the hormone Prolactin, which normally helps women produce milk for breastfeeding.
What does it do? In women, it can cause breast milk leakage and stop periods (making you infertile). In men, it drastically lowers testosterone, causing loss of sex drive and erection problems. If the growth gets big, it can press on the nerves to your eyes, affecting your side vision.
Do I need brain surgery? Usually, NO. This tumour is unique because it melts away with medication. We use a drug called Cabergoline (a tablet taken once or twice a week). It tricks the gland into stopping production and shrinking the tumour. Surgery is only a backup plan.
Can I get pregnant? Once the prolactin levels drop, your periods and fertility will return. We usually stop the drug once you are pregnant.
- Melmed S, et al. Diagnosis and treatment of hyperprolactinemia: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011.
- Casanueva FF, et al. Guidelines of the Pituitary Society for the diagnosis and management of prolactinomas. Clin Endocrinol. 2006.
- Molitch ME. Diagnosis and Treatment of Pituitary Adenomas. JAMA. 2017.