Prolactinoma

Table of Contents

  1. What is a Prolactinoma?
  2. Prolactin Physiology and Hyperprolactinemia
  3. Symptoms in Women
  4. Symptoms in Men
  5. Mass Effects — Visual Field Defects and Headaches
  6. Diagnosis
  7. Treatment — Dopamine Agonists
  8. Surgery, Radiation, and Special Situations
  9. Key Research Papers
  10. Connections
  11. Featured Videos

What is a Prolactinoma?

A prolactinoma is a benign (non-cancerous) tumor of the anterior pituitary gland that produces excess prolactin. It is the most common type of functioning pituitary tumor, accounting for approximately 40% of all pituitary adenomas. Prevalence is estimated at 10–50 per 100,000 people. Prolactinomas are classified by size: microprolactinoma (<10 mm diameter) and macroprolactinoma (≥10 mm). Microprolactinomas are more common in women; macroprolactinomas are more common in men and are typically diagnosed later due to more insidious symptom onset. Malignant prolactin-secreting carcinomas are exceedingly rare (<0.2% of cases).

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Prolactin Physiology and Hyperprolactinemia

Prolactin is secreted by lactotroph cells of the anterior pituitary. Its primary physiological role is initiating and maintaining lactation. Unique among pituitary hormones, prolactin is under tonic inhibitory control by dopamine (from the hypothalamus via the tuberoinfundibular pathway); loss of dopamine inhibition permits prolactin excess. Elevated prolactin suppresses the hypothalamic-pituitary-gonadal axis by inhibiting gonadotropin-releasing hormone (GnRH) pulsatility, leading to reduced LH and FSH secretion. Normal serum prolactin: women <25 ng/mL; men <15 ng/mL. Prolactinoma typically causes levels >100 ng/mL (often >200 ng/mL for macroprolactinomas). Mild elevations (25–100 ng/mL) have a broader differential including medications, hypothyroidism, renal failure, and physiologic stress.

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Symptoms in Women

Hyperprolactinemia in premenopausal women presents as the classic triad: (1) Amenorrhea or oligomenorrhea — disruption of the normal LH/FSH surge. (2) Galactorrhea — spontaneous or expressible milky nipple discharge (in 50–80% of cases). (3) Infertility — anovulation secondary to suppressed gonadotropins. Additional features: decreased libido, vaginal dryness, dyspareunia, osteopenia/osteoporosis (from chronic estrogen deficiency). Postmenopausal women may have few symptoms from hyperprolactinemia itself (ovarian function already absent) and present primarily with tumor mass effects.

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Symptoms in Men

Hyperprolactinemia is often underdiagnosed in men because galactorrhea is uncommon and the gonadal axis symptoms develop insidiously. Presenting features include: erectile dysfunction and decreased libido (from hypogonadotropic hypogonadism), infertility (oligospermia or azoospermia), gynecomastia (rare, caused by reduced testosterone and relative estrogen excess), decreased bone mineral density. Men typically present with larger tumors (macroprolactinomas) at diagnosis, as the gonadal symptoms are less specific and often attributed to other causes.

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Mass Effects — Visual Field Defects and Headaches

Large prolactinomas (macroprolactinomas) may compress adjacent structures. The optic chiasm lies directly above the pituitary fossa; upward extension compresses it, producing bitemporal hemianopsia — loss of peripheral (temporal) vision in both eyes, classically starting with the superior temporal fields. Cavernous sinus invasion causes cranial nerve palsies (CN III, IV, VI — ophthalmoplegia, ptosis, diplopia). Headache from dural stretch is common. Pituitary apoplexy (hemorrhage or infarction into the tumor) is a rare emergency causing sudden severe headache, visual loss, and altered consciousness. Gadolinium-enhanced MRI of the pituitary is the imaging modality of choice.

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Diagnosis

Serum prolactin: The screening test. A single fasting measurement is usually sufficient; stressful venipuncture can cause mild transient elevation (draw after rest). Very high prolactin (>500 ng/mL) is virtually diagnostic of macroprolactinoma. The "hook effect": extremely high prolactin levels can paradoxically appear normal or low on immunoassay — request serial dilutions if MRI shows large tumor with disproportionately "normal" prolactin. Rule out secondary causes: TSH (hypothyroidism raises TRH, stimulating prolactin), medication review (dopamine antagonists: antipsychotics, metoclopramide, domperidone, some antidepressants; proton pump inhibitors; opioids), renal function (impaired clearance), and pregnancy (beta-hCG). Pituitary MRI: characterizes tumor size, invasion, and relationship to optic chiasm.

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Treatment — Dopamine Agonists

Dopamine agonists (DAs) are the first-line treatment for virtually all prolactinomas, including macroprolactinomas, because they suppress prolactin production and directly shrink tumor volume in 80–90% of patients. Cabergoline (preferred): Half-life ~65 hours; dosed twice weekly (0.25–3 mg/week). Superior efficacy and tolerability vs. bromocriptine. Normalizes prolactin in 83% and restores gonadal function in >80%. Tumor shrinkage ≥50% in 70% within 6 months. Side effects: nausea, dizziness, orthostatic hypotension, constipation; rarely, impulse control disorders (gambling, hypersexuality) at higher doses. Bromocriptine: Older, shorter-acting (dosed daily), more nausea; preferred in pregnancy (more safety data). Contraindication: uncontrolled hypertension. Goal: normalize prolactin AND restore gonadal function. After 2 years of normal prolactin + tumor shrinkage, a supervised DA withdrawal trial is reasonable — ~25–30% of microprolactinomas remain in remission off medication.

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Surgery, Radiation, and Special Situations

Transsphenoidal surgery (TSS): Indicated for DA-intolerant/resistant patients, acute visual loss from mass effect not responding to DAs rapidly, or pituitary apoplexy. Cure rates: ~75–90% for microprolactinomas, ~40–50% for macroprolactinomas. Risks: CSF leak, meningitis, hypopituitarism, permanent diabetes insipidus. Radiation: Rarely needed; reserved for malignant or highly aggressive tumors not responding to DAs or surgery; takes years to achieve prolactin normalization. Pregnancy: Bromocriptine is preferred over cabergoline for planned conception (more safety data). Prolactinoma may enlarge during pregnancy (especially macroprolactinomas); monthly visual field monitoring if not resected. TRH effects: Thyrotropin-releasing hormone (TRH) directly stimulates both TSH and prolactin; untreated hypothyroidism causes secondary hyperprolactinemia reversible with thyroid hormone replacement — always check TSH.

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Key Research Papers

  1. Melmed S et al., 2011 — PMID: 21296991 — Endocrine Society clinical practice guideline: Diagnosis and treatment of hyperprolactinemia. J Clin Endocrinol Metab.
  2. Colao A et al., 1994 — PMID: 7969281 — Cabergoline vs. bromocriptine in hyperprolactinemia. N Engl J Med.
  3. Molitch ME, 2017 — PMID: 28586838 — Diagnosis and treatment of pituitary adenomas. JAMA.
  4. Dekkers OM et al., 2010 — PMID: 20164292 — Dopamine agonist withdrawal in prolactinoma. J Clin Endocrinol Metab.
  5. Gillam MP et al., 2006 — PMID: 16682502 — Advances in the treatment of prolactinomas. Endocr Rev.
  6. Schlechte JA, 2003 — PMID: 14679315 — Prolactinoma. N Engl J Med.
  7. Verhelst J et al., 1999 — PMID: 10366406 — Cabergoline in hyperprolactinemia long-term. Eur J Endocrinol.
  8. Casanueva FF et al. — PubMed search: MEN1 pituitary adenoma guidelines — Guidelines for diagnosis and therapy of MEN1 and pituitary adenomas.
  9. Klibanski A, 2010 — PMID: 20375407 — Prolactinomas. N Engl J Med.
  10. Vilar L et al. — PubMed search: cabergoline prolactinoma remission withdrawal — Prolactinoma treatment with cabergoline.
  11. Bronstein MD et al. — PubMed search: prolactinoma pregnancy bromocriptine cabergoline — Prolactinomas in pregnancy.
  12. Ciccarelli A et al. — PubMed search: cabergoline impulse control disorder prolactinoma — Dopamine agonists and impulse control disorders.

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Connections

Research Papers — PubMed Searches

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