Dysmenorrhoea and the PMS–PMDD spectrum — structured SAQ (15 marks)

(a) Classification and pathophysiology (4 marks)

• Classification: primary dysmenorrhoea — painful menstruation in the absence of pelvic pathology, beginning within 6-12 months of menarche, with cramping lower abdominal pain peaking in the first 24-72 hours. (1 mark)^[1]
• Pathophysiology: in the late luteal phase, progesterone withdrawal triggers endometrial release of arachidonic acid. Cyclo-oxygenase (COX) converts arachidonic acid to prostaglandins — chiefly PGF2alpha and PGE2 — and to leukotrienes. (2 marks)^[1]
• Key mediator: PGF2alpha, which causes myometrial contraction and vasoconstriction of the spiral arterioles, producing uterine ischaemia and pain. (1 mark)^[1]

(b) Stepped management and evidence (4 marks)

One mark per step with a correct evidence statement. ^[1]

• Step 1 — NSAID commenced at onset of menstruation (e.g. ibuprofen 400 mg orally three times daily, mefenamic acid 500 mg three times daily, or naproxen 500 mg then 250 mg every 6-8 hours) with topical heat and exercise. The Cochrane review (Marjoribanks 2015) confirms NSAIDs are more effective than placebo.^[1]
• Step 2 — combined oral contraceptive pill or a progestin to suppress ovulation and thin the endometrium, reducing prostaglandin substrate.^[2]
• Step 3 — levonorgestrel intrauterine system for refractory primary dysmenorrhoea.
• Step 4 — investigate for a secondary cause if first-line therapy has not worked at 3-6 months.^[2]

(c) When to investigate and which imaging (2 marks)

• When: if there is no clinical improvement within 3 to 6 months of adequate first-line therapy (ACOG Committee Opinion 760), or sooner if red flags (progressive pain, dyspareunia, abnormal bleeding, a mass). (1 mark)^[2]
• Imaging: transvaginal ultrasound first-line (after sexual activity has been established; transabdominal ultrasound in a sexually inactive adolescent), with MRI for suspected deep infiltrating endometriosis or adenomyosis. (1 mark)^[2]

(d) DSM-5 PMDD criteria (5 marks)

One mark for the symptom count and timing (Criterion A); one mark each for the four Criterion B core symptoms; one mark for confirming by prospective ratings over two cycles. ^[3]

• Criterion A: in the majority of menstrual cycles, at least five symptoms in the final week before onset of menses, starting to improve within a few days of onset and becoming minimal or absent in the week postmenses.
• Criterion B (one or more must be present):
  1. Marked affective lability.
  2. Marked irritability or anger or increased interpersonal conflicts.
  3. Marked depressed mood, feelings of hopelessness, or self-deprecating thoughts.
  4. Marked anxiety, tension, and/or feeling keyed up or on edge.
• Additional Criterion C symptoms (decreased interest, difficulty concentrating, lethargy, appetite change, hypersomnia/insomnia, feeling overwhelmed, physical symptoms) bring the total to five.
• Criterion F: confirmed by prospective daily ratings during at least two symptomatic cycles.^[3]

Common errors that lose marks

• Confusing primary and secondary dysmenorrhoea and offering the wrong first-line therapy.
• Omitting PGF2alpha as the key mediator, or attributing dysmenorrhoea to "contractions" without naming the prostaglandin pathway.
• Investigating immediately instead of giving an empiric 3-to-6-month trial.
• Listing fewer than the four Criterion B symptoms, or giving the wrong symptom count.
• Saying SSRIs are only effective continuously (the Cochrane review supports both continuous and luteal-phase dosing).^[4]

Examiner notes

A high-scoring candidate can name the prostaglandin pathway (NSAID target), knows the 3-to-6-month rule for investigation, and reproduces the DSM-5 PMDD criteria verbatim. Mentioning that SSRIs work in both continuous and luteal-phase dosing is a discriminator. ^[1][3][4]