Overactive Bladder (OAB) is a chronic condition caused by instability of the detrusor or bladder muscle, which gives rise to symptoms of urinary urgency and often urinary incontinence. Idiopathic Detrusor Overactivity (IDO) is a subset of OAB where the cause for the bladder muscle instability is unknown.

OAB is usually treated by conservative measures or with oral medications eg. anticholinergics. Injection of onabotulinum toxin A (onaBoNT-A) into the bladder wall is licenced in the treatment of refractory IDO where oral medications fail. The injected toxin paralyses the bladder by blocking the ability of certain (motor) nerves to communicate with the bladder muscle. As these nerves are mainly concentrated in what is known as the "body" of the bladder this is traditionally where the injections are given.

In addition to its action on motor nerves, onaBoNT-A also affects sensory nerve pathways. Recent studies show that IDO is caused by both motor and sensory nerve dysfunction, therefore injecting the "trigone", a part of the bladder where sensory nerves are particularly dense, may be of clinical benefit. Three studies comparing trigone versus trigone-sparing injection of botulinum toxin in the treatment of IDO have been carried out. One of these indicated a significant benefit in targeting the trigone and the other two did not show any difference.

Our study aims to examine if injection of onaBoNT-A into the trigone alone will provide symptom and functional improvement in patients with IDO by comparing peritrigonal injection of onaBoNT-A with the traditional method of injection which spares the trigone.

Inclusion Criteria:

• Fulfil ICS criteria for OAB
• Urodynamically proven detrusor instability
• Symptoms lasting >6/12
• Patients must discontinue anticholinergic medication >14 days prior to randomisation and withhold the use of anticholinergics for the duration of the study.
• Patients with mixed incontinence are eligible if their urge symptoms are predominant. These will be instruced to record only episodes of urge urinary incontinence.
• Providing informed consent to participate in the study
• At least 18 years of age

Exclusion Criteria:

• Previous BoNT-A injection within 9 months of randomisation
• History of any neurological condition e.g. MS, Parkinsons, CVA
• Contraindication to BoNT e.g. Myaesthenia gravis
• Urinary tract infection in previous 6/12
• Antimicrobial therapy in previous 6/12
• Previous or current diagnosis of prostate or bladder cancer
• History of treatment with cyclophosphamide
• Radiation cystitis
• Urethral dilatation, cystometrogram, bladder cystoscopy under anaesthetic or a bladder biopsy in previous 3/12
• Augmentation cystoplasty, cystectomy or neurectomy
• Urethral stricture of <12ch
• Pregnancy
• Sexually active women of childbearing potential who are unwilling to use contraceptive measures for the duration of the trial.