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Causes
By Mayo Clinic staff
Filling and emptying your bladder is a complex interplay of kidney function, nerve signals and muscle activity. A problem anywhere throughout this system can contribute to overactive bladder and urge incontinence.
Normal bladder function
Your kidneys produce urine, which travels down a pair of long tubes from your kidneys to your bladder. Urine drains from your bladder through an opening at the bottom (neck) and flows out a short tube called the urethra (u-REE-thrah). In women, the urethral opening is located just above the vagina. In men, the urethral opening is at the tip of the penis.
Your bladder expands like a balloon to accommodate the flow of urine. When it's reached about half its capacity, nerve signals alert your brain, and you sense that your bladder is "full." By the time it's three-quarters full, you feel the need to urinate (void). When you urinate, nerve signals coordinate the relaxation of the pelvic floor muscles and the muscles surrounding the neck of the bladder and upper portion of the urethra (urinary sphincter muscles). The muscles of the bladder contract, forcing urine out.
Involuntary bladder contractions
The symptoms of overactive bladder occur in most cases because the muscles of the bladder involuntarily contract. This contraction creates the urgent need to urinate. The urinary sphincter may remain constricted and prevent the bladder from leaking. If the sphincter's strength is overwhelmed by the contraction, then a person experiences urge incontinence.
Causal or contributing factors
In many cases doctors can't exactly identify the causes of overactive bladder. Neurological disorders, such as Parkinson's disease, strokes and multiple sclerosis, are often associated with an overactive bladder.
Several factors may cause or contribute to symptoms similar to those of overactive bladder, and your doctor will try to rule them out during an evaluation because they require other specialized treatments. These factors include:
- High urine production as might occur with high fluid intake, poor kidney function, or diabetes
- Acute urinary tract infections that can cause symptoms very similar to an overactive bladder
- Inflammation of tissues near the urinary tract
- Abnormalities in the bladder, such as tumors or bladder stones
- Factors that obstruct bladder outflow — enlarged prostate, constipation or previous operations to treat other forms of incontinence
- Excess consumption of caffeine or alcohol
- Medications that cause a rapid increase in urine production or require that you take them with lots of fluids
