Bladder filling and emptying is controlled by signals from the brain passing down the spinal cord and along the nerves.
As the bladder fills with urine, messages travel along the nerves from the bladder up the spinal cord to the brain. The brain then sends messages back to the bladder, which stop the emptying reflex. The bladder wall is made of muscle (called the detrusor muscle). When the bladder reaches its capacity the bladder muscle contracts and the urethra (outlet pipe) relaxes and urine is forced out.
When an overactive bladder is diagnosed following bladder function tests, then spontaneous contractions of the detrusor muscle occur during filling. The bladder is on ‘automatic pilot’, emptying whenever it feels full without control from the brain.
Most often treatment includes dietary and fluid changes, bladder retraining, medication and TENs as the first form of treatment. You may already have tried this. If the leakage continues and remains a problem despite this management, then injections of Botulinum toxin, most commonly known as Botox may be considered.