Mixed urinary incontinence with an elevated post-void residual
A 62-year-old woman reports 6 months of urgency, frequency (9 voids/day), and 3 episodes of urge incontinence per week, plus leakage with coughing. She has had two vaginal deliveries and a hysterectomy. Pelvic examination shows a positive cough stress test and stage 1 anterior prolapse. Post-void residual is 160 mL. She tried pelvic floor muscle training for 12 weeks and solifenacin 5 mg, which reduced urgency but caused intolerable dry mouth; she stopped it after 6 weeks. Urodynamics show detrusor overactivity at 180 mL, no detrusor–sphincter dyssynergia, and no obstruction. She is otherwise healthy, takes amlodipine for hypertension, and is reluctant to self-catheterise. She wants "the leakage fixed" and asks about surgery.
1. How would you sequence treatment of her urgency and her stress leakage, and why?
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Her dominant symptom is urgency with frequency and urge incontinence; stress leakage is also present but less frequent. A midurethral sling can worsen urgency and precipitate retention, especially with a residual of 160 mL. I would therefore treat the overactive bladder first and reassess the stress component afterwards.
She has failed behavioural therapy and an antimuscarinic because of side-effects. A beta-3 agonist such as mirabegron 25 mg is a reasonable next step, with blood pressure monitoring because she is hypertensive. If urgency persists, sacral neuromodulation is attractive because it avoids the retention risk of botulinum toxin. Intradetrusor onabotulinumtoxinA 100 U is effective but carries a 5–10% risk of clean intermittent catheterisation, higher with a pre-existing residual; she has already said she is reluctant to catheterise.
Only after the urgency is controlled would I offer a midurethral sling for residual stress incontinence. If the stress leakage were dominant, the sequence could be reversed, but that is not the case here.
2. What is the significance of the 160 mL post-void residual, and how does it change your choice of third-line therapy?
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A residual of 160 mL is abnormal in a woman and raises concern about incomplete emptying, which may be due to detrusor underactivity, detrusor overactivity with poor sustained contraction, or bladder outlet obstruction. Urodynamics here exclude obstruction and show detrusor overactivity, so the residual is likely functional. It still matters because antimuscarinics and botulinum toxin can precipitate retention.
I would avoid escalating antimuscarinic therapy. Mirabegron has a lower retention risk and is a sensible trial. If third-line therapy is needed, sacral neuromodulation is preferable to botulinum toxin in a patient with a residual and reluctance to catheterise. If botulinum toxin is chosen, I would use 100 U rather than a higher dose, counsel about catheterisation, and check the residual at 2 weeks. A residual of 160 mL is not an absolute contraindication, but it shifts the risk–benefit balance.
3. She asks about a midurethral sling. What do you tell her about the risks of worsening urgency and the need for further treatment?
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I would explain that a midurethral sling is effective for stress incontinence, with cure rates around 80–90% at 5 years, but it is not a treatment for urgency. It can improve or worsen urgency, and a small proportion of women develop de novo urgency or voiding dysfunction. Her residual of 160 mL increases the risk of incomplete emptying and temporary or permanent catheterisation.
I would therefore advise treating the urgency first and reassessing. If stress leakage remains bothersome after optimisation, a sling is reasonable. She should understand that further anticholinergic or beta-3 therapy, sacral neuromodulation, or botulinum toxin may still be needed after surgery. This is a shared decision, not a choice between "sling" and "drugs"; the treatments address different components of her mixed incontinence.