A Study to Measure the Effect of Tolterodine Extended Release on the Thickness of the Bladder Wall in Patients With Overactive Bladder

Inclusion Criteria: * Symptoms of overactive bladder (described as urinary urgency, with or without urge incontinence, usually with frequency and nocturia for more than 6 months * Bladder wall thickness of 5mm or more Exclusion Criteria: * Treatment in the previous four weeks with an anticholinergic drug or any drug for the treatment of overactive bladder. * Significant stress incontinence - Urinary tract infection or a history of intermittent urinary tract infections (more than four episodes in the last two years). * Conditions considered significant by the investigator (e.g. cystocoele, significant bladder prolapse, bladder stone, indwelling catheter etc)