First principle: pregnancy first, then a four‑compartment localisation
Then a focused panel — TSH, prolactin, FSH (± estradiol) — localises:
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The compartments and their fingerprints
| Compartment | Cause | Fingerprint |
|---|---|---|
| Ovary | PCOS (commonest pathological) | hyperandrogenism, irregular cycles |
| Ovary | POI | high FSH, hypoestrogenic symptoms <40 |
| Pituitary | prolactinoma | ↑prolactin, ± galactorrhoea/headache/visual field defect |
| Pituitary | Sheehan | PPH → failure to lactate → amenorrhoea 🚩 |
| Hypothalamus | FHA | low energy/exercise/stress; low FSH, low E2 |
| Uterus | Asherman | instrumentation/TB history; normal hormones |
| Systemic | thyroid disease | abnormal TSH |
The localiser (Concept 1, again)
High‑value corrections 🚩
- *No galactorrhoea does not exclude hyperprolactinaemia* (only ~⅓ have it). Confirm modest elevations; consider macroprolactin, drugs.
- FHA: correct the energy deficit (nutrition, reduce excess exercise) — do not just prescribe a pill to induce bleeding (it neither restores the axis nor reliably protects bone).
Pitfalls
- Skipping the pregnancy test; missing a Sheehan history (PPH + no lactation); treating FHA with a COC as if that fixes it.
Pearls
- 🎯 Pregnancy first, then TSH/prolactin/FSH. High FSH = ovary; low FSH = brain. PPH + no lactation = Sheehan.
- 🩺 Ask every secondary‑amenorrhoea patient about weight, exercise, stress, drugs, uterine procedures, and the postpartum course.
Next → The final part — turning physiology into oncology (Concept 37).