Endometriosis affects 1 in 10 women of reproductive age but has an average diagnostic delay of 7–8 years in the UK (APPG on Endometriosis 2020). The key clinical signal is progressive worsening pain that does not respond to NSAIDs and is associated with deep dyspareunia, dyschezia (painful defaecation), and subfertility. PID must be considered in any sexually active woman with pelvic pain and fever — untreated PID causes tubal infertility and ectopic pregnancy. These are the diagnoses most frequently missed in GP consultations for menstrual pain.

The response to NSAIDs is a diagnostic test — prostaglandin-mediated primary dysmenorrhoea responds well to NSAIDs (NNT 3). Failure to respond to adequate NSAIDs should prompt investigation for secondary causes. Progressive worsening is the single most important red flag — primary dysmenorrhoea tends to be stable or improve with age/after childbirth, while secondary causes (especially endometriosis) progressively worsen. Quantifying the impact on daily function (days off work/school) helps justify onward referral and resonates with the RCGP focus on patient-centred outcomes.

Primary dysmenorrhoea affects up to 90% of adolescent women — it is the leading cause of recurrent school absenteeism. The critical distinction is whether this is primary (functional, prostaglandin-driven, responsive to treatment) or secondary (structural, requiring investigation and often specialist intervention). Endometriosis is frequently dismissed as "bad periods" — the RCGP curriculum and NICE NG73 emphasise the importance of early referral to reduce the diagnostic delay that leads to infertility, chronic pain, and reduced quality of life.

Pelvic examination can be deferred in young adolescents who are not sexually active — clinical history is usually sufficient to diagnose primary dysmenorrhoea and initiate treatment. However, in sexually active women or those with suspected secondary causes, examination is mandatory. Recto-vaginal examination (for nodularity in the pouch of Douglas) has a sensitivity of 60–70% for deep endometriosis — it can significantly accelerate referral and laparoscopic diagnosis. Cervical excitation is pathognomonic for PID and requires same-day antibiotics.

NICE NG73 (Endometriosis) explicitly states that a normal ultrasound does NOT exclude endometriosis — peritoneal deposits are invisible on USS. This is a key RCGP exam point. TVUSS is useful for identifying endometriomas, adenomyosis, and fibroids, but a normal scan does not reassure against endometriosis. CA-125 is frequently ordered but has no role in diagnosing endometriosis in primary care — it causes unnecessary anxiety and false positives. Laparoscopy remains the gold standard diagnostic tool for endometriosis.

NICE NG73 states that GPs should refer women with suspected endometriosis to a specialist without waiting for trial of treatment if symptoms are severe. The historical practice of prescribing multiple treatments before referral contributes to the 7–8 year diagnostic delay. In the RCGP SCA, failing to consider endometriosis in a young woman with progressive dysmenorrhoea and dyspareunia is a significant consultation weakness. Chronic pelvic pain with central sensitisation benefits from multidisciplinary pain management, not escalating analgesics.

NSAIDs work by inhibiting cyclo-oxygenase (COX), reducing prostaglandin synthesis — the direct cause of uterine cramping in primary dysmenorrhoea. Starting 1–2 days before expected pain onset is 30% more effective than starting at pain onset. The COCP works by suppressing ovulation (eliminating the prostaglandin surge) and thinning the endometrium — NNT approximately 5 for significant pain reduction. Levonorgestrel IUS reduces menstrual flow by 90% and significantly reduces prostaglandin-mediated pain. GnRH analogues (medical oophorectomy) are highly effective for endometriosis but cause menopausal side effects and bone loss — never used without add-back HRT and specialist supervision.

Heat therapy is genuinely as effective as NSAIDs in RCTs for primary dysmenorrhoea (Cochrane 2014) — it is underutilised and without side effects. TENS is available over-the-counter and is effective, particularly for women who cannot tolerate NSAIDs. Omega-3 supplementation has a modest but statistically significant effect via competitive inhibition of arachidonic acid (a prostaglandin precursor). Psychological interventions (CBT) have strong evidence for chronic pelvic pain — pain catastrophising and central sensitisation are modifiable targets. These measures should be presented as genuine treatment options, not afterthoughts.

NICE NG73 (Endometriosis 2017) states that if empirical treatment (COCP or progestogens) does not control symptoms within 3–6 months, refer to a specialist — do not continue empirical treatment indefinitely. The 7–8 year diagnostic delay in endometriosis is partly attributable to repeated empirical treatments without referral. Functional outcome tracking (days absent from work/school) is more patient-centred than pain scores alone and forms a compelling basis for specialist referral. Safety-netting instructions for ectopic pregnancy are mandatory given the overlap with dysmenorrhoea symptoms.