Primary Dysmenorrhoea

Primary dysmenorrhoea is painful menstruation with no pelvic disease, caused by excess prostaglandin release from the shedding endometrium, which causes uterine contractions and reduced blood flow. It starts within 1 to 2 years of menarche once ovulatory cycles begin, and is very common in young women. It matters because it is a major cause of missed school and work, and responds well to NSAIDs and hormonal treatment.

• Risk factors: early menarche, nulliparity, heavy or long periods, smoking, obesity, family history, premenstrual syndrome.
• Pain starts just before or with bleeding and lasts 8 to 72 hours.
• It lessens with age and after childbirth.

Women have crampy lower abdominal pain that may spread to the back and thighs, with nausea, vomiting, diarrhoea, headache and fatigue, starting a few hours before or at the onset of bleeding and peaking on day 1 or 2. Examination between periods is normal.

• Normal pelvic examination.
• Pain only during menstruation.
• Differential diagnosis: secondary dysmenorrhoea (endometriosis, adenomyosis, fibroids, pelvic inflammatory disease), obstructed uterine or vaginal anomaly, intrauterine device pain, ovarian cyst, urinary tract infection, irritable bowel syndrome, early pregnancy complication.
• Complications: school and work absence, depression and anxiety, sleep disturbance, overuse of analgesics, reduced quality of life.

The diagnosis is clinical, with imaging only when the history suggests another cause.

• History of timing, severity, onset after menarche, bleeding pattern and sexual history; pain score.
• Abdominal examination, and pelvic examination in sexually active women; urine hCG if sexually active.
• Pelvic ultrasound if pain starts after age 25 years, is severe, progressive or not relieved by NSAIDs, or if there is heavy bleeding or dyspareunia.
• Chlamydia and gonorrhoea tests where there is risk; laparoscopy if endometriosis is suspected and treatment fails.

The principle is first line NSAIDs taken at the start of pain or bleeding, with hormonal treatment if pain persists or contraception is wanted.

• Supportive: reassurance and education; heat pack on the lower abdomen; regular exercise; adequate sleep; stop smoking; a pain diary; transcutaneous electrical nerve stimulation where available.
• Pharmacological: ibuprofen 400 mg oral 8-hourly with food (adolescents: 5 to 10 mg/kg per dose, maximum 400 mg per dose and 1200 mg daily), started at the first sign of pain or bleeding and continued for 2 to 3 days; mefenamic acid 500 mg oral 8-hourly with food for 3 days; naproxen 500 mg oral once then 250 mg every 6 to 8 hours for 3 days (maximum 1250 mg on the first day, then 1000 mg daily); diclofenac 50 mg oral 8-hourly with food for 3 days; paracetamol 1 g oral 6-hourly (maximum 4 g in 24 hours; adolescents 15 mg/kg per dose, maximum 60 mg/kg daily) if NSAIDs are contraindicated; hormonal: combined oral contraceptive pill with ethinylestradiol 30 micrograms and levonorgestrel 150 micrograms oral once daily for 21 days then 7 days free (or continuous); levonorgestrel intrauterine system 52 mg for 5 years; depot medroxyprogesterone 150 mg IM every 13 weeks.
• Procedures: none.
• Special groups: women with asthma sensitive to NSAIDs, peptic ulcer, kidney disease, or taking anticoagulants use paracetamol and hormonal treatment; adolescents have weight-based doses and a request for contraception advice if sexually active; women who cannot use oestrogen (migraine with aura, hypertension, previous clot) use progestogen-only methods.
• Red flags: pain not relieved after 3 months of NSAIDs and hormonal treatment, pain starting after age 25 years, pain between periods, dyspareunia, heavy bleeding, fever, pelvic mass, vomiting with collapse.
• Follow-up: review at 3 months; change of drug or addition of hormonal treatment if poor response; ultrasound and gynaecology referral for failure of 2 treatments; review at 6 and 12 months.