The main symptom of urge incontinence (also called hyperactive, irritable, or overactive bladder) is the need to urinate frequently. Patients may go to the bathroom more than 8 times over 24 hours, including 2 or more times a night, and have subsequent leakage. However, most people (60%) with overactive bladder experience only urgency and frequency. In some cases, urge incontinence occurs only at night. This is called nocturnal enuresis.

All cases of urge incontinence involve an overactive bladder. This occurs when the detrusor muscle, which surrounds the bladder, contracts inappropriately during the filling stage. When this occurs, the urge to urinate cannot be voluntarily suppressed, even temporarily. There is usually one of two types:

• Idiopathic Detrusor Overactivity (formerly called Detrusor Instability). In this type, the nerves serving the bladder have signaled the brain appropriately that the bladder is full, but the detrusor muscles are unable to be suppressed. The actual cause, however, is not known.
• Neurogenic Detrusor Overactivity (formerly called Detrusor Hyperreflexia). With this type, a known neurologic problem impairs the signaling systems between the bladder and the central nervous system, and the brain is unable to inhibit the detrusor muscles controlling urination.

Often, the cause of detrusor instability and bladder hyperactivity is unknown. Some conditions that can produce the disorders leading to urge incontinence include the following:

• Benign prostatic hyperplasia (BPH). Detrusor instability occurs in about 75% of men with BPH and causes frequency, urgency, and urination during the night (although incontinence itself occurs only in very severe cases). Urge incontinence only at night can be a sign of severe obstruction in the urinary tract.

• Prostate surgical procedures. Either prostatectomy for prostate cancer or transurethral resection of the prostate (TURP) for BPH can cause detrusor instability. As with stress incontinence, prostatectomy poses a much higher rate than with TURP, which is very low.
• Hysterectomy. Complications of this operation, which removes the uterus, are associated with up to double the risk for eventually needing surgery for incontinence.

• Damage to the central nervous system. Certain neurologic disorders or injuries can disrupt the passage of nerve messages between the urinary tract and central nervous system. These neurological conditions include stroke, multiple sclerosis, spinal cord or disk injury, and Parkinson's disease.
• Infections.
• The aging process.
• Emotional disorders. Anxiety is associated with urge incontinence.
• Medications, including some sleeping pills.
• Genetic factors may play a role in some cases.