A good Q-bank question doesn’t just test if you recognize a diagnosis—it tests whether you can defend it against tempting distractors. Sheehan syndrome is a classic Step endocrine vignette because it ties together obstetrics, pituitary anatomy, and hormone physiology in one scenario. Let’s break down a representative stem, nail the correct answer, then explain why every other option is wrong (or less right).
Tag: Endocrine > Hypothalamus & Pituitary
The Vignette (Classic Sheehan Setup)
A 29-year-old woman presents 2 months postpartum with fatigue, cold intolerance, and inability to breastfeed. Delivery was complicated by severe postpartum hemorrhage requiring transfusion. She also notes amenorrhea and decreased libido. Exam shows bradycardia and dry skin. Labs show low free T4 with inappropriately low TSH, low cortisol, and low prolactin.
Question: What is the most likely underlying cause?
Correct Answer: Postpartum Pituitary Infarction (Sheehan Syndrome)
Why it’s Sheehan
Sheehan syndrome = ischemic necrosis of the anterior pituitary after massive postpartum hemorrhage.
Pathophysiology (the “why now?”)
During pregnancy, estrogen stimulates lactotroph hyperplasia, so the anterior pituitary enlarges and becomes more vulnerable to ischemia. The anterior pituitary is supplied primarily by the hypophyseal portal system (low-pressure venous plexus), making it especially sensitive to hypoperfusion.
Key clinical features (high-yield)
- Agalactorrhea (often the earliest clue) due to ↓ prolactin
- Amenorrhea / infertility due to ↓ LH/FSH
- Secondary hypothyroidism: ↓ T4 with low/normal (inappropriately low) TSH
- Secondary adrenal insufficiency: ↓ cortisol with low ACTH
- Typically no hyperpigmentation (ACTH low)
- Often no hyperkalemia (aldosterone largely preserved, because it’s RAAS-controlled)
Lab pattern you should recognize
Global anterior pituitary hormone deficiency:
- ↓ prolactin, ↓ LH/FSH, ↓ ACTH, ↓ TSH (and often ↓ GH)
Posterior pituitary is usually spared → diabetes insipidus is uncommon in Sheehan.
The “Why Every Answer Choice Matters” Distractor Breakdown
Below are common distractors that show up in Sheehan questions, plus how to eliminate them quickly.
Distractor 1: Lymphocytic Hypophysitis
Why it’s tempting: Also occurs during pregnancy/postpartum, causes pituitary dysfunction.
Why it’s not Sheehan here:
- Typical presentation: headache and visual symptoms from an enlarged pituitary mass (inflammatory swelling)
- Can cause hypopituitarism, but the stem’s big hemorrhage + agalactorrhea strongly points to ischemic necrosis
- Often associated with autoimmune disease (e.g., Hashimoto)
High-yield tell: postpartum + pituitary symptoms with headache/visual field defects → think hypophysitis; postpartum + hemorrhage + agalactorrhea → Sheehan.
Distractor 2: Pituitary Apoplexy (Hemorrhage into Pituitary Adenoma)
Why it’s tempting: Acute pituitary injury with endocrine collapse.
Why it’s not Sheehan here:
- Usually sudden, severe headache, ophthalmoplegia, visual loss
- Often in a patient with known (or silent) pituitary macroadenoma
- Can occur postpartum, but the stem emphasizes postpartum hemorrhagic shock (systemic hypoperfusion), not sudden tumor bleed
High-yield tell: apoplexy is abrupt neuro-ophthalmic emergency; Sheehan is often subacute postpartum endocrine failure.
Distractor 3: Prolactinoma
Why it’s tempting: Pituitary + lactation theme.
Why it’s wrong:
- Prolactinoma causes galactorrhea (not agalactorrhea) and amenorrhea
- Labs: ↑ prolactin, often with ↓ GnRH → ↓ LH/FSH
- No link to postpartum hemorrhage
High-yield pearl:
- Agalactorrhea postpartum = prolactin deficiency (Sheehan)
- Galactorrhea = prolactin excess (prolactinoma, dopamine antagonist meds, hypothyroidism)
Distractor 4: Primary Hypothyroidism (e.g., Hashimoto)
Why it’s tempting: Cold intolerance, fatigue, dry skin.
Why it’s wrong:
- Primary hypothyroidism: ↑ TSH, ↓ T4
- Sheehan: ↓ T4 with inappropriately low/normal TSH (central hypothyroidism)
- The vignette includes other pituitary hormone deficiencies (cortisol, prolactin), which primary thyroid disease cannot explain
Step habit: Always ask—is TSH appropriately responding to the T4?
Distractor 5: Primary Adrenal Insufficiency (Addison Disease)
Why it’s tempting: Fatigue and low cortisol.
Why it’s wrong:
- Addison: high ACTH → hyperpigmentation
- Often hyperkalemia and non–anion gap metabolic acidosis due to aldosterone deficiency
- In Sheehan (secondary AI): ACTH low → no hyperpigmentation, aldosterone preserved → potassium often normal
High-yield comparison
| Feature | Primary AI (Addison) | Secondary AI (Sheehan) |
|---|---|---|
| ACTH | ↑ | ↓ |
| Skin hyperpigmentation | Yes | No |
| Aldosterone | ↓ | Normal (usually) |
| Potassium | ↑ | Normal (usually) |
| Cause | Adrenal gland problem | Pituitary problem |
Distractor 6: Diabetes Insipidus (Posterior Pituitary Failure)
Why it’s tempting: “Pituitary damage” makes people jump to ADH problems.
Why it’s wrong:
- Sheehan primarily affects the anterior pituitary
- DI presents with polyuria, polydipsia, hypernatremia, dilute urine
- Not a typical feature in classic Sheehan stems (and not suggested here)
High-yield anatomy: posterior pituitary is supplied more directly by arterial blood and is relatively resistant to ischemia compared to the anterior pituitary.
Distractor 7: Craniopharyngioma
Why it’s tempting: “Hypothalamus/pituitary” pathology classic.
Why it’s wrong:
- Usually in children (or a separate adult peak), often with headache + bitemporal hemianopsia
- Can cause hypopituitarism, but no connection to postpartum hemorrhage
- Imaging clue: cystic mass with calcifications (from Rathke pouch remnants)
How the Question Writers Want You to Think (Fast Algorithm)
If you see postpartum + hemorrhage:
- Ask: Can’t breastfeed? → ↓ prolactin
- Add: amenorrhea → ↓ LH/FSH
- Add: fatigue/cold intolerance → central hypothyroidism
- Add: low cortisol → secondary adrenal insufficiency
✅ Sheehan syndrome
High-Yield Facts to Memorize (USMLE Style)
- Sheehan syndrome = postpartum anterior pituitary ischemic necrosis after massive hemorrhage
- Earliest/signature clue: failure to lactate (↓ prolactin)
- Hormone deficits: ↓ TSH, ↓ ACTH, ↓ LH/FSH, ↓ prolactin (often ↓ GH)
- No hyperpigmentation, aldosterone preserved
- Distinguish from:
- Lymphocytic hypophysitis (postpartum autoimmune inflammation + headache/visual symptoms)
- Pituitary apoplexy (sudden headache/visual deficits, often adenoma bleed)
Rapid-Fire Mini Table: Sheehan vs Lookalikes
| Condition | Timing/Trigger | Big clue | Hormone pattern |
|---|---|---|---|
| Sheehan | Postpartum hemorrhage | Agalactorrhea | Pan-hypopituitarism (anterior) |
| Lymphocytic hypophysitis | Peripartum autoimmune | Headache ± visual sx, enlarged gland | Variable hypo-pituitarism |
| Pituitary apoplexy | Adenoma hemorrhage | Sudden severe headache, ophthalmoplegia | Acute pituitary failure |
| Prolactinoma | Chronic | Galactorrhea + amenorrhea | ↑ prolactin |
| Addison | Autoimmune adrenalitis | Hyperpigmentation, hyperkalemia | ↑ ACTH, ↓ cortisol |
Takeaway
Sheehan syndrome is the ultimate “context is king” diagnosis: postpartum hemorrhage + agalactorrhea + multi-axis pituitary hormone deficiency. On Step, you don’t get points for recognizing it once—you get points for eliminating every distractor with one or two decisive details.