Overactive bladder

Definition: a symptom syndrome whose hallmark is urinary urgency, usually with frequency (>8 voids/24 h) and nocturia, with or without urgency incontinence, in the absence of infection or other obvious pathology. OAB "wet" = with incontinence; OAB "dry" = without.

Prevalence: about 30% of women and 40% of men aged ≥75 report OAB symptoms; most of the women also have urgency incontinence. Population studies give ranges of 7– 27% in men and 9–43% in women, rising with age.

Pathophysiology: usually detrusor overactivity — involuntary detrusor contractions during filling. Contributory mechanisms are myogenic (patchy denervation, increased spontaneous activity), neurogenic (loss of cortical inhibition in stroke, dementia, parkinsonism), and urothelial/afferent hypersensitivity. The functionally important receptor is the M3 muscarinic receptor; bladder relaxation is mediated by β3-adrenoceptors.

Secondary causes to exclude: UTI, bladder stone, tumour or diverticulum, bladder outlet obstruction, atrophic vaginitis, faecal impaction, poorly compliant bladder after radiotherapy or interstitial cystitis, diabetes, heart failure, and drugs.

DHIC — detrusor hyperactivity with impaired contractility: involuntary contractions but emptying of less than one-third of bladder volume. These patients strain to void, may not have typical urgency symptoms, and are at high risk of retention with antimuscarinics.

Evaluation: history, bladder diary, targeted examination (including pelvic examination in women and DRE in men), urinalysis, and post-void residual where there are emptying symptoms, prior retention, an enlarged prostate, neurological disease, previous incontinence or prostate surgery, or long-standing diabetes. Urodynamics is not routine.

Behavioural therapy (foundation): education, fluid and caffeine modification, weight loss, bladder training with timed voiding and progressive interval lengthening, urge-suppression techniques, and pelvic floor muscle training with biofeedback. In institutional settings, prompted voiding and habit training.

Drug therapy: β3-agonists (mirabegron 25–50 mg, vibegron 75 mg) — preferred in older adults; check renal function and monitor blood pressure. Antimuscarinics (solifenacin, darifenacin, fesoterodine, tolterodine, trospium, oxybutynin) — effective but limited by dry mouth, constipation, blurred vision, raised intraocular pressure, and cognitive impairment and delirium. Trospium and darifenacin have less CNS penetration. Maximum effect may take 1–2 months; if one agent fails, another in the class may still work.

Refractory OAB: intradetrusor botulinum toxin A (chemodenervation, increases capacity, lowers detrusor pressure; repeat not more often than 6-monthly; risk of retention and need for self-catheterisation), sacral neuromodulation (S3), and posterior tibial nerve stimulation.

Supportive measures throughout: pads, liners, barrier creams, external catheters and absorbent washable underwear should be discussed with all patients who leak, together with night-time safety measures to prevent falls.

AUA/SUFU Idiopathic OAB Guideline (2024) abolished the rigid first/second/third-line ladder in favour of shared decision-making, mandated assessment of frailty (Clinical Frailty Scale) and anticholinergic burden, and made patient-reported outcomes central; it also formally recommends discussing containment products with everyone who has urgency incontinence.

β3-agonists are now preferred over antimuscarinics in older and cognitively vulnerable adults, reflecting the cumulative anticholinergic–dementia association and AGS Beers 2023.

Vibegron approved (December 2024) for men with OAB symptoms receiving pharmacological therapy for BPH — the COURAGE trial (~1100 men) showed reduced micturitions, urgency episodes, nocturia and urgency incontinence.

OAB = urgency ± frequency ± nocturia, with or without incontinence; urgency is the hallmark.

~30% of women and ~40% of men aged ≥75 have OAB symptoms.

M3 receptors mediate contraction; β3 receptors mediate relaxation.

DHIC is OAB with poor emptying — antimuscarinics can cause retention.

Urodynamics is not needed to diagnose uncomplicated OAB.

β3-agonist first in the elderly; botulinum toxin and sacral neuromodulation for refractory cases.