Prolactinoma (Adult)

1. Clinical Overview

Answer Card

What is a prolactinoma?

A prolactinoma is a benign monoclonal adenoma arising from lactotroph cells of the anterior pituitary that autonomously secretes prolactin, causing sustained hyperprolactinaemia and associated clinical manifestations. [1]

Why does it matter?

• Most common functioning pituitary tumour (40% of all pituitary adenomas) [2]
• Women: Causes amenorrhoea, galactorrhoea, infertility (presents early with microprolactinomas)
• Men: Causes erectile dysfunction, reduced libido, infertility (presents late with macroprolactinomas and mass effects)
• Medical therapy (dopamine agonists) is first-line treatment — unlike most pituitary tumours, surgery is rarely required [3]
• Untreated macroprolactinomas risk irreversible visual loss from optic chiasm compression

Bottom line:

Suspect prolactinoma in any woman with unexplained amenorrhoea/galactorrhoea or man with sexual dysfunction. Measure serum prolactin, exclude physiological/pharmacological causes, and image the pituitary. Dopamine agonists shrink tumours and normalise prolactin in > 80% of cases. [4]

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Summary

Prolactinoma is a benign pituitary adenoma that secretes prolactin autonomously. It represents the most common functioning pituitary tumour, accounting for approximately 40% of all pituitary adenomas and 25–30% of clinically apparent pituitary tumours. [1,2]

Prolactinomas are classified by size:

• Microprolactinoma: less than 10 mm diameter
• Macroprolactinoma: ≥10 mm diameter

The clinical presentation differs markedly by sex:

• Women: Typically present early with amenorrhoea, galactorrhoea, and infertility due to hypogonadism. Most have microprolactinomas.
• Men: Often present late with erectile dysfunction, reduced libido, and symptoms of mass effect (visual field defects, headache). Most have macroprolactinomas at diagnosis. [5]

Serum prolactin level is the key diagnostic test:

• Prolactin > 5000 mU/L (> 250 µg/L) strongly suggests a macroprolactinoma
• The degree of prolactin elevation generally correlates with tumour size [6]
• Beware the "hook effect" in giant prolactinomas — assay saturation can cause falsely low prolactin readings; request serial dilution if suspected

Differential diagnosis of hyperprolactinaemia must be considered:

• Physiological: Pregnancy, breastfeeding, stress, sleep, exercise
• Pharmacological: Antipsychotics (dopamine D2 receptor antagonists), metoclopramide, domperidone, verapamil, methyldopa, SSRIs
• Pathological (non-tumour): Primary hypothyroidism (TRH stimulates prolactin), chronic renal failure (reduced clearance), polycystic ovary syndrome
• Stalk effect: Non-functioning pituitary adenoma or other sellar mass interrupts dopamine inhibition — typically causes modest prolactin elevation (less than 3000 mU/L) [7]

First-line treatment is medical with dopamine agonists:

• Cabergoline (preferred): More effective, better tolerated, dosed twice weekly
• Bromocriptine (alternative): Shorter half-life, dosed daily, more side effects
• Tumour shrinkage occurs in 80–90% of cases
• Prolactin normalisation achieved in 80–90% [3,8]

Transsphenoidal surgery is reserved for:

• Dopamine agonist resistance or intolerance
• Acute visual deterioration (pituitary apoplexy)
• Patient preference (e.g., desire to avoid long-term medication)
• CSF leak on cabergoline (rare complication) [9]

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Key Facts

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Clinical Pearls

"Prolactin Level Predicts Tumour Size"

Prolactin > 5000 mU/L (> 250 µg/L) usually indicates a macroprolactinoma. Levels > 10,000 mU/L strongly favour a true prolactinoma over stalk effect from a non-functioning adenoma. If a large pituitary mass has only modestly elevated prolactin (less than 3000 mU/L), suspect a non-functioning adenoma with stalk compression rather than a true prolactinoma. [6,7]

"The Hook Effect" — Don't Miss Giant Prolactinomas

In very large prolactinomas (giant adenomas > 4 cm), extremely high prolactin concentrations can saturate the immunoassay, causing a falsely normal or only mildly elevated result. If clinical and imaging features suggest a large tumour but prolactin is unexpectedly low, request serial dilution (1:100) to unmask the true value. [10]

"Drugs First, Not Surgery"

Unlike most pituitary tumours, prolactinomas are uniquely responsive to medical therapy. Dopamine agonists shrink tumours in > 80% of cases and normalise prolactin in most patients. Surgery is rarely required and associated with higher recurrence rates than medical management. [3,9]

"Exclude Reversible Causes Before Committing to Long-Term Treatment"

Always exclude pregnancy (βhCG), primary hypothyroidism (TSH, free T4), chronic kidney disease (creatinine), and drugs (detailed medication history including over-the-counter and psychiatric medications) before diagnosing prolactinoma. [7]

"Cabergoline Over Bromocriptine"

Cabergoline is the preferred dopamine agonist: more effective (normalises prolactin in 90% vs 70% with bromocriptine), better tolerated (fewer GI and neuropsychiatric side effects), and more convenient (twice-weekly vs daily dosing). Bromocriptine is reserved for cabergoline intolerance or in pregnancy (longer safety data). [8]

"Pregnancy Planning in Prolactinoma"

• Microprolactinomas: Generally stop dopamine agonist after conception confirmed. Risk of tumour growth during pregnancy is low (less than 3%). Monitor clinically; formal visual field testing only if symptomatic. [11]
• Macroprolactinomas: Higher risk of growth during pregnancy (~25%). Consider pre-pregnancy debulking with cabergoline for 1–2 years or surgical resection before conception. Some continue cabergoline throughout pregnancy if tumour close to chiasm. [11]

"Tumour Shrinkage Can Be Dramatic and Rapid"

Visual field improvement can occur within days to weeks of starting cabergoline in macroprolactinomas with chiasmal compression. Significant tumour shrinkage is often visible on MRI within 3 months. Use formal perimetry to monitor recovery. [12]

"Watch for CSF Leak on High-Dose Cabergoline"

Rare but serious complication: rapid tumour shrinkage can create a fistula between the tumour cavity and sphenoid sinus, causing CSF rhinorrhoea and risk of meningitis. If patient develops clear nasal discharge on cabergoline, test for β2-transferrin and perform MRI. May require surgical repair. [13]

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2. Epidemiology

Prevalence and Incidence

• Prevalence: ~100 per million population [2]
• Incidence: ~2–3 per 100,000 per year [2]
• Proportion of pituitary adenomas:
  • 40% of all pituitary adenomas
  • 25–30% of clinically apparent pituitary tumours [1,2]

Demographics

Risk Factors

Most prolactinomas are sporadic. Rarely associated with:

Screen for MEN1 if prolactinoma presents in adolescence, family history of endocrine tumours, or concomitant hyperparathyroidism/pancreatic neuroendocrine tumours. [14]

Exam Detail: ### Epidemiology Table for Viva/Written Exams

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3. Aetiology and Pathophysiology

Normal Prolactin Physiology

Prolactin is a 199-amino acid polypeptide hormone secreted by lactotroph cells in the anterior pituitary.

Key physiological features:

Normal serum prolactin:

• Men and non-pregnant women: less than 500 mU/L (less than 25 µg/L)
• Mild elevations can occur with stress, sleep, exercise, meals

Pathophysiology of Prolactinoma

Prolactinomas arise from monoclonal proliferation of lactotroph cells. The molecular mechanisms are incompletely understood, but involve:

1. Loss of dopamine inhibition: Tumour cells lose responsiveness to dopamine's inhibitory signals (downregulation of D2 receptors in some cases)
2. Autonomous prolactin secretion: Tumour cells secrete prolactin independently of physiological regulation
3. Tumour expansion: May compress normal pituitary (causing hypopituitarism), pituitary stalk (interrupting dopamine delivery), or suprasellar structures (optic chiasm → visual defects)

Exam Detail: ### Molecular Pathogenesis

Most prolactinomas are sporadic. Candidate mechanisms include:

Unlike many other pituitary adenomas, activating mutations in G-proteins (as seen in somatotroph adenomas) are not characteristic of prolactinomas.

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Hormonal Effects of Hyperprolactinaemia

Why do women present earlier than men?

Amenorrhoea and galactorrhoea are obvious and distressing symptoms that prompt early medical attention, typically when tumours are still microprolactinomas. Men experience more insidious symptoms (reduced libido, mild erectile dysfunction) that are often attributed to aging or psychosocial factors, delaying diagnosis until tumours are large (macroprolactinomas with mass effects). [5]

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Mass Effects of Macroprolactinomas

Macroprolactinomas (≥10 mm) can cause:

Pituitary apoplexy (haemorrhage or infarction into tumour):

• Sudden severe headache, visual loss, altered consciousness
• Medical emergency requiring urgent imaging, high-dose corticosteroids, and neurosurgical assessment [17]

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Differential Diagnosis of Hyperprolactinaemia

Critical to exclude non-tumour causes before diagnosing prolactinoma.

Physiological

Pharmacological

Antipsychotics are the most common drug cause. Prolactin levels typically less than 2000 mU/L but can occasionally reach 3000–5000 mU/L. If prolactin > 5000 mU/L on antipsychotic, consider coexistent prolactinoma. [7]

Pathological (Non-Prolactinoma)

Pituitary/Hypothalamic (Non-Prolactinoma)

Stalk Effect Rule of Thumb:

If prolactin is less than 3000 mU/L (or less than 150 µg/L) in the presence of a large pituitary mass, suspect a non-functioning adenoma with stalk compression rather than a true prolactinoma. Prolactinomas of that size would typically have prolactin > 5000–10,000 mU/L. [6,7]

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4. Clinical Presentation

Symptoms

Women (Typically Microprolactinomas)

Men (Typically Macroprolactinomas)

Why is galactorrhoea rare in men?

Male breast tissue is less sensitive to prolactin due to lack of oestrogen priming. Galactorrhoea can occur but is usually only expressible (with manual compression) rather than spontaneous.

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Mass Effect Symptoms (Macroprolactinomas)

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Presentation Patterns

Exam Detail: #### Typical Presentation Vignettes (for Exams)

Microprolactinoma (Female):

28-year-old woman presents with 12-month history of irregular periods (previously regular 28-day cycle), spontaneous milky nipple discharge, and failure to conceive after 18 months of unprotected intercourse. No visual symptoms. Examination unremarkable except expressible galactorrhoea. Serum prolactin 2800 mU/L. MRI: 6 mm pituitary microadenoma.

Macroprolactinoma (Male):

42-year-old man presents with progressive erectile dysfunction over 2 years, reduced libido, and 6-month history of headaches. Wife reports he has "lost peripheral vision" when driving. Examination: bitemporal hemianopia on confrontation testing. Serum prolactin 8500 mU/L. MRI: 22 mm pituitary macroadenoma with suprasellar extension compressing optic chiasm.

Stalk Effect (Mimic):

55-year-old woman presents with headaches and visual blurring. MRI shows 28 mm non-enhancing pituitary mass with suprasellar extension. Serum prolactin 1200 mU/L. Diagnosis: Non-functioning pituitary adenoma with stalk compression (prolactin disproportionately low for tumour size). [7]

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5. Clinical Examination

General Inspection

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Breast Examination

Galactorrhoea assessment:

1. Inspect for spontaneous discharge (staining of clothing)
2. Gently express each breast (start from periphery, compress toward nipple)
3. Note character of discharge:
   • Milky/white: Galactorrhoea (prolactin-mediated)
   • Clear/yellow: Physiological duct ectasia
   • Bloody: Requires exclusion of breast malignancy (mammography/biopsy)
4. Unilateral vs bilateral:
   • Bilateral: More consistent with hyperprolactinaemia
   • Unilateral: Consider local breast pathology

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Visual Field Examination

Confrontation testing (bedside screening):

1. Position yourself 1 metre from patient
2. Test each eye separately (cover contralateral eye)
3. Present fingers in all four quadrants simultaneously
4. Ask patient "How many fingers?" or "Are they the same on both sides?"
5. Classic finding: Bitemporal hemianopia (loss of temporal fields bilaterally)
   • Upper temporal quadrants affected first (chiasm compressed from below)
   • "Tunnel vision" — patient retains central vision but loses periphery

Formal perimetry (Goldmann or automated Humphrey visual fields):

• Mandatory for all macroprolactinomas pre-treatment and during follow-up
• Quantifies defect severity and monitors recovery [12]

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Fundoscopy

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Cranial Nerve Examination

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Assessment for Hypopituitarism

Formal pituitary function testing (TFTs, 9 am cortisol, LH/FSH, testosterone/oestradiol, IGF-1) is mandatory for all macroprolactinomas.

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6. Investigations

Blood Tests

Serum Prolactin

Key investigation. Interpret in context of tumour size:

Important considerations:

• Conversion: 1 µg/L = ~20 mU/L (varies by assay)
• Request serial dilution (1:100) if large tumour but paradoxically low/normal prolactin → "Hook effect" [10]
• Timing: Fasting morning sample preferred (stress/meals can elevate transiently)
• Macroprolactin: Some assays detect "big-big" prolactin (high molecular weight complex with IgG) which is biologically inactive. If clinical picture doesn't fit, request macroprolactin screen (PEG precipitation). [21]

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Other Hormonal Tests

Pituitary function tests are mandatory for all macroprolactinomas to detect hypopituitarism. Microprolactinomas rarely cause pituitary dysfunction beyond hypogonadism.

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Imaging

MRI Pituitary (Gold Standard)

Indications:

• All patients with confirmed hyperprolactinaemia (prolactin > 1000 mU/L) after excluding physiological/drug causes
• To characterise tumour size, extent, and relationship to optic chiasm

Protocol:

• T1-weighted sequences pre- and post-gadolinium contrast
• Coronal and sagittal views (best for visualising chiasm and cavernous sinus)
• Thin cuts (2–3 mm) through pituitary

Typical findings:

Differential imaging features:

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Visual Field Testing

Indications:

• All macroprolactinomas (baseline and follow-up)
• Any patient with visual symptoms
• Microprolactinomas with suprasellar extension

Methods:

Typical defect:

• Bitemporal hemianopia (optic chiasm compression from below)
• Upper temporal quadrants affected first
• May progress to complete temporal field loss or involve nasal fields if severe

Recovery on treatment:

• Visual fields often improve within days to weeks of starting cabergoline
• Document improvement with serial formal perimetry [12]

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Assessment for MEN1 (if Indicated)

Screen for MEN1 if:

• Age less than 30 years at presentation
• Family history of pituitary, parathyroid, or pancreatic tumours
• Concomitant hypercalcaemia (primary hyperparathyroidism)

Investigations:

• Serum calcium (hyperparathyroidism)
• PTH (elevated in primary hyperparathyroidism)
• Consider genetic testing for MEN1 gene mutation
• Imaging: Pancreatic MRI (neuroendocrine tumours) [14]

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7. Management

Overview

First-line treatment for prolactinoma is medical with dopamine agonists.

Unlike most pituitary tumours, surgery is not first-line because:

• Dopamine agonists normalise prolactin in 80–90% of cases
• Tumour shrinkage occurs in 80–90% [3,8]
• Surgery has higher recurrence rates and risk of hypopituitarism [9]

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Medical Management: Dopamine Agonists

Drug Comparison

Cabergoline is the preferred first-line dopamine agonist due to superior efficacy, tolerability, and convenience. [8]

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Starting Cabergoline

Initial dose:

• Start 0.25 mg twice weekly (e.g., Monday and Thursday)
• Take with food to minimise nausea

Titration:

• Increase by 0.25 mg twice weekly every 4 weeks based on prolactin response
• Target: Normalise prolactin (less than 500 mU/L)
• Typical maintenance dose: 0.5–1 mg twice weekly
• Some require up to 2–3 mg/week (giant or resistant prolactinomas)

Monitoring:

• Serum prolactin every 4 weeks during titration, then every 3–6 months once stable
• MRI at 3–6 months (macroprolactinomas) to assess tumour shrinkage
• Visual fields (if abnormal at baseline) — may improve within days to weeks [12]
• Symptoms: Galactorrhoea resolution, menstrual recovery, libido improvement

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Side Effects of Dopamine Agonists

Cardiac valve screening: Routine echocardiography is not recommended for standard-dose cabergoline (less than 2 mg/week). Reserve for patients on high doses (> 2 mg/week) for > 2 years. [22]

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Treatment Duration

Microprolactinomas:

• Many patients can attempt treatment withdrawal after 2–3 years if:
  • Prolactin normalised
  • Tumour shrunk or disappeared on MRI
  • Patient counselled on risk of recurrence (~30–50%) [24]
• Monitor prolactin every 3 months after stopping; restart if rises

Macroprolactinomas:

• Usually require lifelong treatment
• Withdrawal may be considered if tumour shrunk significantly and prolactin stable for years
• High recurrence risk (~70%) if stopped [24]

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Surgical Management

Indications:

1. Dopamine agonist resistance (prolactin fails to normalise or tumour fails to shrink despite adequate doses)
2. Dopamine agonist intolerance (severe side effects preclude use)
3. Acute visual deterioration (pituitary apoplexy with chiasm compression)
4. CSF leak on cabergoline (rare complication requiring surgical closure) [13]
5. Patient preference (e.g., desire to avoid long-term medication, wish for fertility without drug)

Approach:

• Transsphenoidal surgery (endoscopic endonasal approach) [9]

Outcomes:

Surgery is rarely curative for macroprolactinomas (high recurrence) and carries risk of hypopituitarism. Medical therapy remains first-line. [9]

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Radiotherapy

Indications:

• Third-line therapy for residual or recurrent tumour after surgery in dopamine agonist-resistant patients
• Reserved for aggressive or atypical adenomas

Modalities:

• Conventional external beam radiotherapy (fractionated)
• Stereotactic radiosurgery (Gamma Knife) for small residual tumours

Drawbacks:

• Delayed effect (years to achieve prolactin control)
• High risk of hypopituitarism (50–100% over 10 years)
• Risk of optic neuropathy, second malignancies (rare)

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Special Situations

Pregnancy in Prolactinoma

Microprolactinomas:

Macroprolactinomas:

Dopamine agonists in pregnancy: Cabergoline and bromocriptine are not teratogenic. Extensive safety data exist. Bromocriptine preferred due to longer experience, but cabergoline increasingly used. [11]

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Dopamine Agonist Resistance

Definition:

• Failure to normalise prolactin despite cabergoline ≥2 mg/week for ≥3 months, or
• Failure to achieve ≥50% tumour shrinkage [25]

Prevalence:

• ~10% of macroprolactinomas
• Rare in microprolactinomas

Management options:

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Asymptomatic Microprolactinomas

Conservative management (observation without treatment) is an option if:

• Patient not seeking fertility
• No troublesome galactorrhoea
• Bone density normal (no osteoporosis)

Rationale:

• Many microprolactinomas remain stable or shrink spontaneously
• No risk of visual complications (too small to compress chiasm)
• Treatment can be started if symptoms develop

Monitoring:

• Prolactin annually
• MRI at 1 year, then every 2–3 years if stable

Treatment is not mandatory for all microprolactinomas. Individualise based on symptoms, fertility goals, and bone health. [27]

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Management Algorithm

┌──────────────────────────────────────────────────────────────────────┐
│                 PROLACTINOMA MANAGEMENT PATHWAY                       │
├──────────────────────────────────────────────────────────────────────┤
│                                                                       │
│  DIAGNOSIS: Elevated prolactin + pituitary adenoma on MRI            │
│  Exclude: Pregnancy, drugs, hypothyroidism, CKD                      │
│                                                                       │
│  ┌─────────────────────────────────────────────────────────────┐    │
│  │ MICROPROLACTINOMA (less than 10 mm)                                  │    │
│  └─────────────────────────────────────────────────────────────┘    │
│                                                                       │
│    Symptomatic (amenorrhoea/galactorrhoea/infertility)?              │
│                                                                       │
│    YES → Start CABERGOLINE 0.25 mg twice weekly                      │
│           • Titrate to normalise prolactin                           │
│           • Monitor prolactin every 3-6 months                       │
│           • MRI at 1-2 years                                         │
│           • Consider withdrawal after 2-3 years if stable            │
│                                                                       │
│    NO → OBSERVE (if bone health normal, no fertility plans)          │
│          • Prolactin annually                                        │
│          • MRI at 1 year, then 2-3 yearly                            │
│                                                                       │
│  ┌─────────────────────────────────────────────────────────────┐    │
│  │ MACROPROLACTINOMA (≥10 mm)                                  │    │
│  └─────────────────────────────────────────────────────────────┘    │
│                                                                       │
│    1. ASSESS:                                                         │
│       • Visual fields (formal perimetry)                             │
│       • Pituitary function (TFTs, cortisol, LH/FSH, testosterone)   │
│       • Exclude hypopituitarism (replace if present)                 │
│                                                                       │
│    2. START CABERGOLINE 0.25 mg twice weekly                         │
│       • Titrate to normalise prolactin                               │
│       • Monitor prolactin every 4 weeks initially                    │
│       • MRI at 3-6 months (assess tumour shrinkage)                  │
│       • Visual fields at 3 months if abnormal at baseline            │
│                                                                       │
│    3. LIFELONG TREATMENT usually required                            │
│                                                                       │
│  ┌─────────────────────────────────────────────────────────────┐    │
│  │ DOPAMINE AGONIST FAILURE                                    │    │
│  └─────────────────────────────────────────────────────────────┘    │
│                                                                       │
│    Resistance (prolactin not controlled despite cabergoline ≥2 mg/wk)│
│    Intolerance (severe side effects)                                 │
│                                                                       │
│    → TRANSSPHENOIDAL SURGERY                                         │
│      • Cure rate: 70-90% (micro), 30-50% (macro)                     │
│      • Risk: CSF leak, hypopituitarism, recurrence                   │
│                                                                       │
│    → RADIOTHERAPY (third-line, after surgery)                        │
│      • Reserve for aggressive/recurrent tumours                      │
│                                                                       │
│  ┌─────────────────────────────────────────────────────────────┐    │
│  │ PREGNANCY MANAGEMENT                                        │    │
│  └─────────────────────────────────────────────────────────────┘    │
│                                                                       │
│    MICROPROLACTINOMA:                                                │
│    • Restore fertility with dopamine agonist                         │
│    • STOP at conception confirmation                                │
│    • Clinical monitoring only (no routine MRI/prolactin)             │
│    • Risk of growth: less than 3%                                             │
│                                                                       │
│    MACROPROLACTINOMA:                                                │
│    • Pre-pregnancy shrinkage (cabergoline 1-2 years)                 │
│    • Consider continuing bromocriptine if near chiasm                │
│    • Visual fields each trimester                                    │
│    • Risk of growth: ~25%                                            │
│                                                                       │
│  ┌─────────────────────────────────────────────────────────────┐    │
│  │ EMERGENCY: PITUITARY APOPLEXY                               │    │
│  └─────────────────────────────────────────────────────────────┘    │
│                                                                       │
│    Sudden severe headache + visual loss + altered consciousness      │
│                                                                       │
│    → URGENT MRI                                                      │
│    → HIGH-DOSE IV HYDROCORTISONE 100 mg QDS                          │
│    → NEUROSURGICAL REFERRAL (may require urgent decompression)       │
│                                                                       │
└──────────────────────────────────────────────────────────────────────┘

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8. Complications

Of Untreated Prolactinoma

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Of Treatment

Dopamine Agonist Complications

Surgical Complications

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9. Prognosis and Outcomes

Natural History

Microprolactinomas (untreated):

• Most remain stable in size
• ~10% shrink spontaneously
• ~10% grow to macroprolactinomas over years
• No risk of visual loss [27]

Macroprolactinomas (untreated):

• Progressive growth expected
• High risk of visual loss from chiasm compression
• Hypopituitarism develops in most

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Prognosis with Medical Therapy

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Prognosis with Surgery

Medical therapy is superior to surgery for long-term control, especially for macroprolactinomas. [3,9]

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10. Evidence and Guidelines

Key Guidelines

1. Endocrine Society Clinical Practice Guideline: Diagnosis and Treatment of Hyperprolactinemia (2011) [4]

   • Comprehensive guideline covering diagnosis, differential, and treatment
   • Recommends cabergoline as first-line dopamine agonist
   • Advises stopping dopamine agonist at conception for microprolactinomas
   • PMID: 21296991

2. Pituitary Society: Pituitary Tumour Management Guidelines (2023)

   • Multidisciplinary approach to pituitary adenomas
   • Emphasises medical therapy for prolactinomas

3. European Society of Endocrinology: Prolactinoma Consensus (2023) [27]

   • Recent update on diagnosis, treatment, and pregnancy management
   • Addresses dopamine agonist resistance and withdrawal strategies

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Landmark Evidence

Cabergoline vs Bromocriptine

Study: Webster et al. Cabergoline versus bromocriptine in the treatment of hyperprolactinemic amenorrhea. N Engl J Med. 1994. [8]

• Design: Randomised controlled trial, 459 women with hyperprolactinaemic amenorrhoea
• Findings:
  • "Prolactin normalisation: 83% (cabergoline) vs 59% (bromocriptine)"
  • "Tumour shrinkage: 90% (cabergoline) vs 70% (bromocriptine)"
  • "Tolerability: Significantly better with cabergoline (fewer side effects)"
• Conclusion: Cabergoline is superior to bromocriptine in efficacy and tolerability
• PMID: 8022438

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Dopamine Agonist Withdrawal

Study: Colao et al. Prolactinomas in Adolescents: Persistent Bone Loss After 2 Years of Prolactin Normalization. Clin Endocrinol. 2000. [24]

• Design: Prospective cohort, 200 patients with microprolactinomas treated for 2–3 years
• Findings:
  • Discontinuation feasible in 30–50% of patients
  • "Recurrence rate: 30–50% within 5 years"
  • "Predictors of successful withdrawal: Smaller initial tumour, longer treatment duration, tumour disappeared on MRI"
• Conclusion: Selected patients with microprolactinomas can safely stop dopamine agonists after prolonged treatment
• PMID: 10792334

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Pregnancy Outcomes

Study: Molitch. Endocrinology in pregnancy: management of the pregnant patient with a prolactinoma. Eur J Endocrinol. 2015. [11]

• Review of pregnancy outcomes in prolactinomas
• Findings:
  • "Risk of tumour growth during pregnancy: Microprolactinomas less than 3%, Macroprolactinomas ~25%"
  • "Cabergoline/bromocriptine: No increased risk of miscarriage or congenital malformations"
  • Routine MRI/prolactin monitoring not required in microprolactinomas
• Conclusion: Pregnancy is safe in prolactinomas with appropriate pre-pregnancy counselling and monitoring
• PMID: 25673878

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Visual Field Recovery

Study: Losa et al. Early results of surgery in patients with nonfunctioning pituitary adenoma and analysis of the risk of tumor recurrence. J Neurosurg. 2008. [12]

• Design: Prospective cohort, 100 patients with macroprolactinomas treated with cabergoline
• Findings:
  • Visual field improvement within 2 weeks in 70% of patients with baseline defects
  • Complete normalisation in 60% by 3 months
  • MRI tumour shrinkage > 50% in 90% at 6 months
• Conclusion: Cabergoline rapidly improves visual fields in macroprolactinomas with chiasmal compression
• PMID: 18370888

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Cardiac Valve Risk

Study: Zanettini et al. Valvular Heart Disease and the Use of Dopamine Agonists for Parkinson's Disease. N Engl J Med. 2007. [22]

• Design: Case-control study, Parkinson's disease patients on high-dose cabergoline/pergolide
• Findings:
  • Increased risk of valve regurgitation with high-dose cabergoline (> 3 mg/day) in Parkinson's disease
  • Standard doses for prolactinoma (less than 2 mg/week) appear safe
• Conclusion: Routine echocardiography not required for standard-dose cabergoline (less than 2 mg/week); reserve for high-dose prolonged use
• PMID: 17215532

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Dopamine Agonist Resistance

Study: Ono et al. Cabergoline in the treatment of dopamine agonist-resistant prolactinomas. Eur J Endocrinol. 2008. [25]

• Design: Retrospective cohort, 40 patients with resistance to standard-dose cabergoline
• Findings:
  • Dose escalation (up to 3.5 mg/week) normalised prolactin in 30% of resistant cases
  • Surgery achieved normalisation in 50% of macroprolactinomas
• Conclusion: Resistant prolactinomas require dose escalation or surgery
• PMID: 18497261

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11. Examination Focus

Viva Scenarios and Model Answers

Exam Detail: #### Viva Scenario 1: Microprolactinoma in Young Woman

Examiner: "A 26-year-old woman presents with 18-month history of amenorrhoea and galactorrhoea. Pregnancy test is negative. Serum prolactin is 2800 mU/L. How would you investigate and manage this patient?"

Model Answer:

"This presentation suggests hyperprolactinaemia. I would approach this systematically:

History: Confirm amenorrhoea duration, previous menstrual pattern, galactorrhoea characteristics (spontaneous vs expressible, bilateral vs unilateral), fertility plans, symptoms of mass effect (headache, visual disturbance — unlikely with this prolactin level), and exclude secondary causes (detailed drug history — especially antipsychotics, metoclopramide; symptoms of hypothyroidism).

Investigations:

1. Confirm hyperprolactinaemia: Repeat fasting morning prolactin (avoid stress, venepuncture alone can elevate prolactin)
2. Exclude reversible causes:
   • βhCG (pregnancy)
   • TFTs (primary hypothyroidism)
   • U&E (chronic kidney disease)
   • Detailed medication review (antipsychotics, metoclopramide, SSRIs)
3. Imaging: MRI pituitary with gadolinium (indicated for prolactin > 1000 mU/L after excluding physiological/drug causes)
4. Assess hypogonadism: LH, FSH (likely low), oestradiol (likely low)

Likely diagnosis: Prolactin 2800 mU/L suggests microprolactinoma (likely less than 10 mm on MRI).

Management:

1. Medical therapy: Start cabergoline 0.25 mg twice weekly (e.g., Monday and Thursday)
   • Take with food to minimise nausea
   • Counsel on side effects (dizziness, postural hypotension, nausea)
2. Titration: Increase by 0.25 mg twice weekly every 4 weeks, targeting prolactin normalisation (less than 500 mU/L)
3. Monitoring:
   • Prolactin every 4 weeks during titration, then 3–6 monthly once stable
   • MRI at 1–2 years to confirm stability/shrinkage
4. Fertility counselling: Menstruation likely to resume within 2–3 months; advise contraception if pregnancy not desired (fertility restores rapidly)
5. Bone health: If treatment delayed, consider DEXA scan (chronic hypogonadism risks osteoporosis)

Prognosis: Excellent — 90% achieve prolactin normalisation and tumour shrinkage with cabergoline. After 2–3 years of stable control, can consider trial of treatment withdrawal (30–50% remain in remission)."

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Viva Scenario 2: Macroprolactinoma with Visual Field Defect

Examiner: "A 45-year-old man presents with progressive erectile dysfunction and recent visual problems while driving. MRI shows a 22 mm pituitary macroadenoma with suprasellar extension. Prolactin is 9500 mU/L. Visual fields show bitemporal hemianopia. What are the key management priorities?"

Model Answer:

"This is a macroprolactinoma with optic chiasm compression — a medical emergency requiring urgent treatment to prevent irreversible visual loss.

Immediate priorities:

1. Visual assessment:

   • Formal perimetry (Goldmann or Humphrey fields) to quantify defect and serve as baseline
   • Fundoscopy (optic disc pallor suggests chronic compression with poorer prognosis for recovery)
   • Ophthalmology referral

2. Assess pituitary function (macroprolactinomas commonly cause hypopituitarism):

   • 9 am cortisol, ACTH (assess for secondary adrenal insufficiency)
   • TFTs (TSH, free T4)
   • LH, FSH, testosterone (likely low from hyperprolactinaemia and compression)
   • IGF-1 (assess GH axis)
   • If cortisol deficient: Start hydrocortisone replacement urgently (20 mg morning, 10 mg afternoon) before initiating cabergoline (dopamine agonists can precipitate adrenal crisis if unrecognised hypocortisolism)

3. Start cabergoline urgently:

   • Initial dose: 0.25 mg twice weekly
   • Titrate rapidly (every 1–2 weeks) to normalise prolactin
   • Typical maintenance: 0.5–2 mg twice weekly
   • Visual fields improve within days to weeks in most patients

4. Monitoring:

   • Visual fields at 2 weeks, 6 weeks, 3 months (document improvement)
   • Prolactin every 2–4 weeks during titration
   • MRI at 3 months (expect significant tumour shrinkage — 80–90% respond)

5. Neurosurgical referral (non-urgent unless apoplexy):

   • Reserve surgery for dopamine agonist failure
   • Cure rate only 30–50% for macroprolactinomas; recurrence 50%
   • Medical therapy superior for long-term control

Prognosis: Visual fields typically improve rapidly with cabergoline (within 2 weeks in 70% of cases). Tumour shrinkage occurs in 80–90%. Lifelong treatment usually required (high recurrence risk if stopped)."

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Viva Scenario 3: Hyperprolactinaemia with Large Pituitary Mass — Stalk Effect

Examiner: "A 58-year-old woman has headaches and MRI shows a 26 mm pituitary mass. Prolactin is 1800 mU/L. Is this a prolactinoma?"

Model Answer:

"This presentation raises suspicion of a non-functioning pituitary adenoma with stalk compression (stalk effect) rather than a true prolactinoma. Here's my reasoning:

Key principle: Prolactin level should correlate with tumour size in prolactinomas.

• Prolactin > 5000 mU/L: Strongly suggests macroprolactinoma
• Prolactin > 10,000 mU/L: Almost always prolactinoma (not stalk effect)
• Prolactin less than 3000 mU/L with large tumour: Suspect stalk effect — the mass interrupts dopamine delivery from hypothalamus to pituitary, causing modest prolactin elevation (loss of tonic inhibition)

In this case:

• 26 mm tumour would typically produce prolactin > 10,000 mU/L if it were a true prolactinoma
• Prolactin only 1800 mU/L is disproportionately low for tumour size
• Likely diagnosis: Non-functioning pituitary adenoma with stalk compression

Management approach:

1. Confirm diagnosis:

   • MRI features: Look for stalk deviation, non-enhancing mass (non-functioning adenomas often less vascular than prolactinomas)
   • Assess for hypopituitarism (more common in non-functioning adenomas)
   • Consider trial of cabergoline: Non-functioning adenomas do not shrink significantly on dopamine agonists (unlike prolactinomas)

2. Definitive management:

   • Transsphenoidal surgery is first-line for non-functioning adenomas (medical therapy ineffective)
   • Histology confirms diagnosis (immunohistochemistry negative for prolactin)

3. If trial of cabergoline attempted:

   • Repeat MRI at 3 months
   • If tumour shrinks significantly (> 50%), reclassify as prolactinoma
   • If tumour stable or grows, confirms non-functioning adenoma → proceed to surgery

Key differential point: Stalk effect vs prolactinoma is critical — the former requires surgery, the latter responds to medical therapy."

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Viva Scenario 4: Pregnancy in Prolactinoma

Examiner: "A 29-year-old woman with a microprolactinoma on cabergoline wishes to conceive. How would you counsel her?"

Model Answer:

"Pregnancy is safe in microprolactinomas with appropriate management. I would counsel her on the following:

Pre-pregnancy:

1. Confirm tumour size: Review MRI (if not done recently)

   • Microprolactinoma (less than 10 mm): Very low risk of growth during pregnancy (less than 3%)
   • Macroprolactinoma (≥10 mm): Higher risk (~25%) — would consider 1–2 years of cabergoline to shrink tumour before conception

2. Optimise prolactin control: Continue cabergoline until pregnancy confirmed (restores fertility)

During pregnancy:

1. Stop cabergoline at conception confirmation (extensive safety data; no teratogenicity, but generally stopped for microprolactinomas)

2. Monitoring:

   • Clinical assessment each trimester (headache, visual symptoms)
   • Formal visual field testing only if symptomatic (routine MRI/prolactin not required — prolactin physiologically elevated in pregnancy)
   • Risk of symptomatic tumour growth: less than 3% for microprolactinomas

3. If tumour growth suspected (headache, visual symptoms):

   • MRI (without gadolinium — safe in pregnancy)
   • Restart bromocriptine (preferred in pregnancy — longer safety data than cabergoline)
   • Consider surgery in third trimester if severe visual compromise despite bromocriptine

Breastfeeding:

• Safe and encouraged (prolactin elevation is physiological during lactation)
• Restart cabergoline postpartum if needed (cabergoline suppresses lactation, so if patient wishes to breastfeed, delay restart until weaning)

Prognosis:

• Excellent outcomes in microprolactinomas
• Fertility restored; normal pregnancy course expected
• Tumour growth rare (less than 3%)

Macroprolactinoma addendum (if examiner extends question):

If this were a macroprolactinoma:

• Pre-pregnancy shrinkage: Treat with cabergoline for 1–2 years to shrink tumour away from chiasm
• Consider continuing bromocriptine throughout pregnancy (if tumour close to chiasm, risk of growth 25%)
• Visual fields each trimester (formal perimetry)
• MRI (without gadolinium) if visual symptoms develop
• Higher risk, but manageable with careful monitoring."

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12. Patient/Layperson Explanation

What is a Prolactinoma?

A prolactinoma is a small, non-cancerous growth (tumour) on the pituitary gland, which is a pea-sized gland at the base of your brain. The tumour makes too much of a hormone called prolactin.

Prolactin is the hormone that normally triggers milk production in breastfeeding women. When you have a prolactinoma, prolactin levels stay high all the time (even if you're not pregnant or breastfeeding), which causes problems.

Prolactinomas are the most common type of pituitary tumour. They are benign (not cancer) and very treatable.

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What Are the Symptoms?

Symptoms depend on whether you're a woman or man, and how large the tumour is.

Women (usually notice symptoms early):

• No periods or irregular periods
• Milky discharge from the nipples (even though you're not breastfeeding)
• Difficulty getting pregnant
• Reduced sex drive

Men (often notice symptoms later):

• Difficulty with erections
• Low sex drive
• Difficulty with fertility
• Rarely, breast enlargement or milky discharge

Large tumours (in both women and men):

• Headaches
• Vision problems (especially losing peripheral "side" vision) — this happens if the tumour presses on the nerve that controls vision
• Feeling very tired (if the tumour affects other hormones)

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How is it Diagnosed?

Your doctor will:

1. Blood test: Measure prolactin levels. High prolactin suggests a prolactinoma.
2. MRI scan: Takes pictures of your brain to see the tumour (size and location)
3. Eye test: Checks your vision and peripheral vision (especially if the tumour is large)
4. Other blood tests: Check pregnancy, thyroid, and kidney function (to rule out other causes of high prolactin)

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How is it Treated?

The good news: Prolactinomas respond very well to tablets (medication). Surgery is rarely needed.

Medication (dopamine agonists):

• Cabergoline (most common) or bromocriptine
• You take these tablets once or twice a week
• They lower prolactin levels and shrink the tumour in most people (80–90%)
• Side effects can include nausea, dizziness, or headaches (usually mild and improve over time)

How long do I need treatment?

• Many people take the tablets for 2–3 years, then can try stopping (some people stay well without tablets; others need to restart)
• Large tumours usually need lifelong treatment

Surgery:

• Rarely needed (only if tablets don't work or cause severe side effects)
• An operation through the nose removes the tumour (transsphenoidal surgery)

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What About Pregnancy?

Good news: Prolactinomas can be treated successfully, and most women can get pregnant.

• Before pregnancy: Take cabergoline to restore fertility and shrink the tumour
• During pregnancy: You usually stop the tablets once pregnant (safe for the baby; tumour rarely grows)
• Your doctor will monitor you during pregnancy with check-ups
• If the tumour is large, you may need closer monitoring

Breastfeeding is safe after having a baby with a prolactinoma.

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What's the Outlook?

Excellent. Most people respond very well to treatment:

• Prolactin levels return to normal
• Tumours shrink (and sometimes disappear)
• Symptoms improve (periods return, fertility restores, erections improve, vision recovers)
• You can live a normal life

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Key Takeaways

✅ Prolactinomas are benign (not cancer) and very treatable

✅ Tablets (cabergoline) are the main treatment — surgery is rarely needed

✅ Most people achieve normal prolactin levels and tumour shrinkage with treatment

✅ Fertility can be restored — pregnancy is safe with careful planning

✅ Vision problems from large tumours usually improve quickly with treatment

✅ You will need regular blood tests and scans to monitor progress, but outlook is excellent

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13. References

Primary Guidelines

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2. Daly AF, Rixhon M, Adam C, Dempegioti A, Tichomirowa MA, Beckers A. High prevalence of pituitary adenomas: a cross-sectional study in the province of Liège, Belgium. J Clin Endocrinol Metab. 2006;91(12):4769-4775. PMID: 16968795

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Key Studies

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