Overactive bladder and urgency urinary incontinence — structured SAQ (15 marks)

(a) Working diagnosis and first-line pharmacological management (4 marks)

One mark for diagnosis; one mark each for agent, dose, route, and patient-specific reasoning. ^[1][3]

• Working diagnosis: overactive bladder (OAB) syndrome per the ICS 2002 standardisation — urgency, with or without urge incontinence, usually with frequency and nocturia, in the absence of infection (negative urinalysis) or other cause. Differential acknowledged (urge incontinence, OAB-wet subtype).^[1]
• First-line pharmacological agent: mirabegron 25 mg orally once daily, titrated to 50 mg once daily based on efficacy and tolerability.^[2][3]
• Route: oral, swallowed whole with liquids, with or without food.^[2]
• Patient-specific reason for choice: her age (68), MoCA 27/30 (mild cognitive concern) and obesity. Mirabegron is a β3-adrenoceptor agonist with dry mouth at placebo level and no measurable cognitive-decline signal in prevalent-user dementia cohorts, whereas oxybutynin IR carries an adjusted odds ratio for dementia of 4.53 in cohort studies and tolterodine 5.64.^[6]
• Pre-treatment checks: baseline blood pressure (severe uncontrolled hypertension is a contraindication), review of interacting drugs (digoxin and metoprolol exposure warrant caution), and counselling on hypertension surveillance during treatment.^[2][3]

(b) Alternatives to discuss and their respective safety considerations (4 marks)

One mark per agent with safety framing. ^[3][6]

• Solifenacin 5 mg daily (titrated to 10 mg): M3-selective antimuscarinic; better incontinence outcomes than tolterodine ER 4 mg in the STAR trial at 4 weeks (44% additional reduction in incontinence episodes). Lower cognitive penetration than oxybutynin IR. Caution: dry mouth, constipation, glaucoma, urinary retention.^[3]
• Tolterodine ER 4 mg daily: bladder-selective antimuscarinic; useful in working-age women. Dementia signal of approximately 5-fold increased adjusted odds in prevalent-user cohorts (Iwai 2026) — discuss with the patient.^[6]
• Darifenacin 7.5-15 mg daily or trospium 20 mg twice daily: M3-selective darifenacin or quaternary-amine trospium — both have lower CNS penetration and are alternatives where cognition is a concern, but with similar peripheral anticholinergic adverse effects.^[3]
• Oxybutynin IR 5 mg two-to-three times daily: non-selective antimuscarinic that crosses the BBB; in this 68-year-old with a MoCA of 27/30, it is the wrong starting rung — explain why (cognitive safety, dry mouth, falls) and reserve for fit younger patients.^[6]

(c) Escalation at 12 weeks — partial response (5 marks)

One mark per option with dose, consent issue and trigger for invasive therapy. ^[3][4]

• Up-titrate mirabegron to 50 mg once daily if tolerated and BP allows — the phase III pooled analysis (Nitti 2013) reported greater efficacy at 50 mg than 25 mg, with the dry-mouth advantage preserved.^[2]
• Add an antimuscarinic (e.g. solifenacin 5 mg) for combination therapy in incomplete responders on mirabegron monotherapy. Discuss additive anticholinergic burden if she later crosses 75.^[3]
• Switch class — replace mirabegron with solifenacin 5 mg titrated to 10 mg, or vice versa; re-evaluate at 4 weeks. Reassess bother at every visit using a validated questionnaire (PPBC, OAB-q).^[3]
• Trigger for third-line invasive therapy: persistent bothersome urge incontinence after two lines of pharmacotherapy (e.g. an antimuscarinic and mirabegron, alone or in combination), confirmed on bladder diary, with urodynamics if diagnostic uncertainty or prior pelvic surgery.^[3][4]

(d) Refractory OAB and invasive options (2 marks)

One mark for definition; one mark for the three options with key complication.^[1]

• Refractory OAB = bothersome OAB symptoms persisting after failure of behavioural therapy and at least two lines of pharmacotherapy (typically an antimuscarinic and mirabegron, alone or in combination).^[3]
• Intradetrusor onabotulinumtoxinA 100 U (idiopathic OAB) sparing the trigone — key complication: intermittent self-catheterisation in approximately 5-10% with 100 U, plus UTI risk.^[4]
• Sacral neuromodulation (InterStim, staged tined-lead test at S3) — key complication: lead migration, infection, pain at implant site, MRI-conditional device, eventual battery replacement.^[5]
• Percutaneous tibial nerve stimulation (PTNS) — 12 weekly 30-minute sessions — key complication: minor local bruising or discomfort at the needle site; efficacy modest versus sham.^[3]