Sheehan syndrome is one of those “classic USMLE” diagnoses that shows up as a postpartum patient who can’t breastfeed—and the real test is recognizing that the underlying problem is pituitary ischemic necrosis after obstetric hemorrhage. If you understand the why (physiology of pregnancy + shock), the symptoms and lab patterns become much easier to predict.
Big Picture (What Sheehan Syndrome Is)
Sheehan syndrome = postpartum hypopituitarism due to ischemic necrosis of the pituitary gland, classically after massive postpartum hemorrhage (often with hypotension/shock).
The one-liner you should memorize
Postpartum hemorrhage → pituitary infarction (esp. anterior pituitary) → low pituitary hormones → agalactorrhea + amenorrhea ± adrenal insufficiency/hypothyroidism.
Why Pregnancy Sets You Up (Pathophysiology)
During pregnancy, the anterior pituitary enlarges substantially—mainly due to lactotroph hyperplasia (estrogen effect) in preparation for lactation.
- Bigger gland = higher metabolic demand
- Pituitary blood supply is via the hypophyseal portal system, a relatively low-pressure venous system
- So if the patient has severe blood loss during delivery → hypoperfusion → ischemic necrosis, predominantly affecting the anterior pituitary
What gets hit?
- Anterior pituitary hormones: FSH, LH, ACTH, TSH, Prolactin = “FLAT-P”
- Posterior pituitary involvement can occur but is less common (different blood supply).
- This is why diabetes insipidus is not the classic presentation.
High-Yield Clinical Presentation
Timing clue
Symptoms often begin immediately postpartum (e.g., failure to lactate) or evolve over weeks to months (e.g., hypothyroid symptoms, amenorrhea).
Classic symptoms by hormone deficiency
↓ Prolactin
- Agalactorrhea (failure to lactate) — very high yield
↓ GnRH axis (↓ FSH/LH)
- Amenorrhea/oligomenorrhea
- Infertility
- Decreased libido, vaginal dryness
↓ ACTH (secondary adrenal insufficiency)
- Fatigue, weakness
- Hypotension, dizziness
- Hypoglycemia
- Nausea, abdominal pain
Key Step distinction:
Secondary adrenal insufficiency → low cortisol but NO hyperpigmentation (low ACTH) and typically no hyperkalemia (aldosterone preserved because it’s regulated by RAAS).
↓ TSH (central hypothyroidism)
- Cold intolerance, weight gain, constipation, bradycardia
- Low free T4 with inappropriately low/normal TSH
± Growth hormone deficiency (adults)
- Decreased muscle mass, increased fat mass, low energy (nonspecific)
“Buzzword” Vignette Patterns (USMLE-Style)
Most classic:
Postpartum patient with massive hemorrhage + hypotension → now can’t breastfeed and has amenorrhea.
Other clues:
- History of blood transfusion, uterine atony, retained placenta, placenta accreta, prolonged labor
- Symptoms of secondary adrenal insufficiency (fatigue + hypotension + hypoglycemia)
Diagnosis: What to Order and What You’ll See
Step 1-level hormone pattern (predictable)
Anterior pituitary failure → low pituitary hormones + low target gland hormones.
| Axis | Pituitary hormone | Target hormone | Expected in Sheehan |
|---|---|---|---|
| Lactotroph | Prolactin | — | ↓ prolactin |
| Thyroid | TSH | Free T4 | ↓ TSH (or inappropriately normal) + ↓ T4 |
| Adrenal | ACTH | Cortisol | ↓ ACTH + ↓ cortisol |
| Gonadal | LH/FSH | Estradiol | ↓ LH/FSH + ↓ estradiol |
| Growth | GH | IGF-1 | ↓ IGF-1 (often) |
Imaging
- MRI pituitary may show an empty sella later or signs of pituitary infarction/atrophy.
Dynamic testing (Step 2-ish nuance)
If uncertainty remains, endocrinology may use stimulation tests (e.g., ACTH stimulation). But for exams, the postpartum hemorrhage history + hormone deficits usually clinches it.
Must-Know Differentials (How USMLE Tries to Trick You)
Sheehan vs Lymphocytic hypophysitis
Both can be postpartum and cause hypopituitarism.
| Feature | Sheehan syndrome | Lymphocytic hypophysitis |
|---|---|---|
| Trigger | Massive postpartum hemorrhage | Autoimmune inflammation, often late pregnancy/postpartum |
| Mechanism | Ischemic necrosis | Lymphocytic infiltration |
| Key clue | Agalactorrhea after hemorrhage/shock | Headache/visual symptoms from pituitary enlargement may be more prominent |
| Imaging | Empty sella later | Enlarged pituitary/stalk thickening (often) |
Sheehan vs Pituitary apoplexy
- Pituitary apoplexy: acute hemorrhage into a pituitary adenoma → sudden severe headache, visual field defects, ophthalmoplegia.
- Sheehan: postpartum ischemia after hemorrhage; headache/visual symptoms are not the core presentation.
Sheehan vs Prolactinoma
- Prolactinoma causes galactorrhea + amenorrhea (high prolactin)
- Sheehan causes agalactorrhea (low prolactin)
Treatment (And the Order Matters)
1) Stabilize first if adrenal insufficiency is suspected
If the patient is hypotensive, hypoglycemic, very ill postpartum, or labs suggest cortisol deficiency:
- Give stress-dose glucocorticoids (e.g., hydrocortisone) first
High-yield rule: Replace cortisol before thyroid hormone.
Starting levothyroxine first can increase cortisol clearance and precipitate adrenal crisis.
2) Long-term hormone replacement (as needed)
- Glucocorticoids (secondary adrenal insufficiency)
- Levothyroxine (central hypothyroidism—dose guided by free T4, not TSH)
- Estrogen/progestin replacement (if not seeking pregnancy) or fertility therapy if desired
- Consider GH replacement in select adults (less board-relevant)
3) Counseling & follow-up
- Many patients require lifelong endocrinology follow-up
- Education about stress dosing steroids during illness/surgery (if ACTH deficiency)
High-Yield Associations & “Testable Extras”
Common exam associations
- Postpartum hemorrhage (uterine atony, placenta accreta, retained products) → Sheehan
- Failure to lactate is often the earliest clue
- Amenorrhea after delivery is not “normal postpartum” if prolonged and accompanied by other pituitary deficits
Key lab distinctions (secondary vs primary endocrine failure)
- Secondary adrenal insufficiency: low ACTH → no hyperpigmentation, often normal K+
- Central hypothyroidism: low free T4 with inappropriately low/normal TSH
- Hypogonadotropic hypogonadism: low LH/FSH → low estrogen
First Aid Cross-References (How It’s Usually Organized)
In First Aid for the USMLE Step 1, Sheehan syndrome is typically referenced under:
- Endocrine → Pituitary disorders → Hypopituitarism
- Concepts tied to:
- Anterior pituitary hormones (FLAT-P)
- Secondary adrenal insufficiency vs primary
- Postpartum endocrine syndromes
Use First Aid’s pituitary table to quickly anchor:
- Which hormones come from anterior vs posterior pituitary
- What “secondary” endocrine failure looks like on labs
Rapid Review (Last-Minute Checklist)
- Definition: Postpartum anterior pituitary infarction after hemorrhage
- Mechanism: Enlarged anterior pituitary in pregnancy + hypoperfusion → necrosis
- Classic findings: Agalactorrhea + amenorrhea ± fatigue/hypotension (low cortisol)
- Labs: Low pituitary hormones + low target hormones (central hypothyroidism, secondary adrenal insufficiency)
- Tx: Glucocorticoids first, then thyroid and other hormone replacement