Endocrinology

Pituitary Disorders

Clinical overview and exam mastery guide for prolactinoma, acromegaly, diabetes insipidus, and SIADH with pathway-directed pharmacology.

Most Common Adenoma
Prolactinoma
Acromegaly First-Line
Surgery
Central DI
Desmopressin
SIADH
Fluid restriction first

Pituitary High-Yield Branches

Anterior Prolactin GH/ACTH/TSH/LH/FSH Posterior ADH Oxytocin Board focus Prolactinoma Acromegaly, DI, SIADH Strategy is secretion control plus consequence management Lower excess hormone effects or replace deficient ADH signaling as needed

Tumor control and water-balance correction dominate management questions.

1. Pituitary Physiology (Foundation First)

Anterior Pituitary Hormones

  • ACTH, TSH, GH, prolactin, LH, FSH

Posterior Pituitary Hormones

  • ADH (vasopressin), oxytocin

2. Prolactinoma

Most common pituitary adenoma.

Pathophysiology and Features

  • Excess prolactin suppresses GnRH and lowers LH/FSH
  • Women: galactorrhea, amenorrhea, infertility
  • Men: low libido, erectile dysfunction

First-Line Therapy

  • Dopamine agonists: cabergoline, bromocriptine
  • MOA: dopamine receptor stimulation inhibits prolactin secretion and shrinks tumor
  • Side effects: nausea, orthostatic hypotension, headache
  • Caution: uncontrolled hypertension contexts
  • Cabergoline is usually preferred for tolerability

3. Acromegaly

Clinical Pattern

  • Enlarged hands/feet
  • Coarse facial features
  • Cardiomegaly and glucose dysregulation

Management

  • First-line: surgical resection
  • Persistent disease: medical therapy escalation
Drug MOA Major Side Effects Notes
Somatostatin analogues (octreotide, lanreotide) Suppress GH secretion and lower IGF-1 GI upset, gallstones Common post-surgical adjunct class
Pegvisomant GH receptor antagonist blocking peripheral GH action Liver enzyme elevation, injection site reactions Used when biochemical control remains inadequate

4. Diabetes Insipidus (DI)

Types and Features

  • Central DI: ADH deficiency
  • Nephrogenic DI: renal ADH resistance
  • Clinical pattern: polyuria, polydipsia, hypernatremia

Therapy

  • Central DI: desmopressin
  • Nephrogenic DI: thiazides plus low-sodium diet
Drug MOA Major Side Effects Notes
Desmopressin ADH analogue acting at V2 receptors to increase collecting-duct water reabsorption Hyponatremia, water retention Indicated for central DI
Thiazide diuretics (nephrogenic DI) Reduce distal sodium delivery and increase proximal water reabsorption, lowering urine volume Hypokalemia, hyponatremia, dehydration risk Classic paradoxical urine reduction mechanism

5. SIADH (Syndrome of Inappropriate ADH)

Pattern and Causes

  • Excess ADH causes water retention and dilutional hyponatremia
  • Common causes: small-cell lung cancer, CNS disease, medications
  • Labs: low sodium and low serum osmolality

Treatment Strategy

  • Mild/moderate: fluid restriction
  • Severe symptomatic hyponatremia: hypertonic saline (careful correction)
  • Resistant cases: V2 antagonists such as tolvaptan

Tolvaptan

  • MOA: V2 receptor antagonism promotes free-water excretion
  • Side effects: thirst, hepatotoxicity risk
  • Used selectively in difficult or persistent SIADH cases

Management Recap Drill

Prolactinoma: cabergoline first-line dopamine agonist.
Acromegaly: surgery first, then somatostatin analogue if persistent.
Central DI: desmopressin replacement.
Nephrogenic DI: thiazide-based volume strategy.
SIADH: fluid restriction first, tolvaptan for resistant cases.

Visual Algorithm Placeholder

[Insert Pituitary Disorder Diagnostic and Treatment Flowchart Here During UI Integration]

Guideline References (Management)

Endocrine Society Clinical Practice Guidelines

https://www.endocrine.org

Guideline Scope

  • Hyperprolactinemia management
  • Acromegaly treatment escalation
  • DI and SIADH management standards

6. Common Exam Traps

Cabergoline is preferred first-line for prolactinoma.
Thiazides can paradoxically reduce urine volume in nephrogenic DI.
SIADH typically shows low sodium with low serum osmolality.
Desmopressin treats central DI, not classic nephrogenic DI.
Pegvisomant blocks GH receptor effects rather than GH secretion.

7. Quick Revision Summary

Must Remember

  • Pituitary acts as a master endocrine regulator
  • Prolactinoma responds to dopamine agonists
  • Acromegaly often starts with surgical control
  • DI reflects inadequate ADH effect
  • SIADH reflects excessive ADH effect

Practice Questions Placeholder

  • Topic: Pituitary Disorders
  • Subtopics: prolactinoma, acromegaly, diabetes insipidus, SIADH, vasopressin antagonists