OVERACTIVE BLADDER

Overactive bladder - Definition
Overactive bladder (OAB) is a symptom syndrome which includes urgency, with or without urge incontinence, frequency, and nocturia. The symptoms are usually caused by bladder (detrusor) overactivity, but can be due to other forms of voiding dysfunction. 17% of the population >40 years old in Europe have symptoms of OAB.10

Conventional treatment
Conservative
Patient management involves a multidisciplinary team approach (urologists, gynaecologists, continence nurse specialists, physiotherapists, and community-based health care workers). Treat any underlying causes (urethral obstruction, bladder stones, spinal disease, or tumour). TURP for bladder outlet obstruction due to BPH can provide symptomatic relief in >66% of men. Treatment of SUI component includes pelvic floor exercises, biofeedback, and high-frequency electrical stimulation (which strengthens the pelvic floor and sphincter by increasing tone through sacral neural feedback systems).

Behavioural modification
This involves modifying fluid intake, avoiding stimulants (caffeine, alcohol), and bladder training for urgency (delay micturition for increasing periods of time by inhibiting the desire to void).

Medication
50% of patients will benefit from medication.
- Anticholinergic drugs act to inhibit bladder contractions and increase capacity (oxybutynin, tolterodine; trospium; propiverine). Oxybutynin also exerts a direct muscle effect and can be administered directly into the bladder (intravesically) in patients performing intermittent catheterization (5mg in 30ml normal saline 8 hourly after emptying the bladder). Contraindications: closed angle glaucoma. Side-effects: dry mouth, constipation, blurred vision.
- Tricyclic antidepressants (imipramine) exert a direct relaxant effect on bladder muscle as well as producing sympathomimetic and central effects.
- Desmopressin (DDAVP) is a synthetic vasopressin analogue which acts as an antidiuretic. It is used intranasally to alleviate nocturia in adults. Oral DDAVP is effective for nocturnal polyuria.
- Baclofen is a GABA receptor agonist, which is used orally or via intrathecal pump in patients with bladder dysfunction and limb spasticity.

Neuromodulation
This involves electrical stimulation of the bladder's nerve supply to suppress reflexes responsible for involuntary bladder muscle (detrusor) contraction.
- The  Interstim  device stimulates the S3 afferent nerve which then inhibits detrusor activity at the level of the sacral spinal cord. An initial percutaneous nerve evaluation is performed, followed by surgical implantation of permanent electrode leads into the S3 foramen, with a pulse generator which is programmed externally.
- SANSâ„¢ (Stoller Afferent Nerve Stimulator) is a minimally invasive technique which accesses the sacral nerve junction via the posterior tibial nerve near the ankle. Its efficacy is questionable.

Surgery
The aim is to increase functional bladder capacity, decrease maximal detrusor pressure, and protect the upper urinary tract.
Auto-augmentation (detrusor myectomy): detrusor muscle is excised from the dome of bladder, leaving the underlying bladder endothelium intact. A large epithelial bulge is created which augments bladder capacity.

Augmentation enterocystoplasty ( Clam  ileocystoplasty): relieves intractable frequency, urge, and UUI in 90% of patients. The bladder dome is cut open (bivalved) and a detubularized segment of ileum is anastomosed, creating a larger bladder volume.

Conduit diversion: a non-continent urinary outlet. Typically, both ureters are anastomosed and connected to a short ileal pouch, which is brought out cutaneously as a stoma.

Intravesical pharmacotherapy
Botulinum toxin A (BTX-A) injection therapy acts by inhibiting calcium-mediated release of ACh at the neuromuscular junction, reducing muscle contractility. It is used predominantly for neuropathic bladder dysfunction, but increasingly is being used for failed medical therapy of the OAB in non-neuropaths. It is injected directly into detrusor muscle under cystoscopic guidance (flexible cystoscopy or rigid under regional or general anaesthetic) at 20 - 30 random sites, excluding the trigone (dose dependent on supplier's recommended dose schedule). Repeat treatments are required (6 - 12 months between injections), and ISC may be needed to empty residuals (5% of non-neuropaths). Mild flu-like reactions lasting a week or so can occur. Generalized weakness, swallowing or breathing difficulty rarely reported. Allergic reactions uncommon.