15. Dysmenorrhoea: primary versus secondary

First principle: two categories, one discriminating question

• Primary — anatomically normal pelvis; pain from PGF₂α‑driven myometrial hypercontractility and ischaemia. Onset 6–12 months after menarche (once cycles become ovulatory).
• Secondary — pain due to identifiable disease; onset later, often in a woman whose periods were previously painless.

Discriminators pointing to secondary

• Onset years after menarche; dyspareunia, dyschezia, cyclical bowel/bladder symptoms (endometriosis); menorrhagia + bulky tender uterus (adenomyosis); abnormal bleeding/mass (fibroid); fever/discharge/CMT (PID). 🚩

Management logic

• Primary: NSAIDs (block prostaglandin synthesis) ± combined hormonal contraception (suppress ovulation → thinner endometrium → less prostaglandin).
• Secondary: treat the underlying disease — analgesia alone is inadequate.

Pitfalls

• Dismissing progressively worsening or late‑onset dysmenorrhoea as "just cramps" — this is how endometriosis is missed for years.

Pearls

• 🎯 Primary = prostaglandins + normal pelvis; secondary = find the disease.
• 🩺 A good NSAID trial and a careful history for secondary features is the correct first move — the two aren't mutually exclusive.

Next → The commonest "secondary" endocrine disorder starts with visible androgen excess (Concept 16).