First principle: ask breasts? uterus? then FSH
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The signature diagnoses and their discriminators
| Diagnosis | Karyotype | Uterus | Breasts | Key clue |
|---|---|---|---|---|
| Imperforate hymen | 46,XX | present | present | cyclic pain + haematocolpos, bulging bluish membrane (cryptomenorrhoea) |
| MRKH | 46,XX | absent | present | normal pubic hair, functioning ovaries |
| CAIS | 46,XY | absent | present | sparse pubic hair, testes, male‑range testosterone |
| Turner | 45,X | present | poor | short stature, high FSH, streak ovaries |
| Swyer | 46,XY | present | poor | XY gonadal dysgenesis; gonadectomy for tumour risk 🚩 |
| Kallmann | 46,XX/XY | present | poor | anosmia, low FSH/LH |
The two exam‑defining contrasts
- MRKH vs CAIS (both: breasts +, uterus −): MRKH = 46,XX + normal hair; CAIS = 46,XY + sparse hair.
- Turner vs Kallmann (both: low estrogen): Turner = high FSH (ovarian); Kallmann = low FSH + anosmia (central).
- CAIS vs Swyer (both 46,XY): CAIS uterus absent (AMH acted); Swyer uterus present (no AMH).
Pitfalls / corrections
- "Karyotype is the best first test for everyone" — outdated. Reason with breasts/uterus/pelvic ultrasound + gonadotropins first, then karyotype when a chromosomal/gonadal cause is suspected. 🚩
- Missing imperforate hymen — a normal‑axis, surgically curable cause presenting with cyclic pain.
Pearls
- 🎯 Breasts? Uterus? FSH? solves most of primary amenorrhoea. Absent uterus → MRKH (XX, normal hair) vs CAIS (XY, sparse hair).
- 🩺 Cyclic pain + no menses + bulging membrane = imperforate hymen — examine the introitus.
Next → When menses start and then stop (Concept 36).