Incontinence is classified by both causes and symptoms. The two most common types are called urge incontinence and stress incontinence. Urge incontinence is primarily bladder "misbehavior," and as such is characterized by spontaneous and uncontrolled urine leakage often accompanied by the overwhelming sensation of needing to void. This condition is also referred to as bladder instability or overactive bladder. Many people with this condition also have difficulty with bowel control and report frequent bowel movements or difficulties with constipation.
The causes of urge incontinence are not clearly known. It is likely that changes in the nerves controlling the bladder or the bladder muscle itself play important roles. Learned voiding behaviors, ageing, hormonal changes, prior childbirth, previous surgery, dietary habits and other factors appear to influence this condition.
In contrast to urge incontinence, stress incontinence is primarily due to weakness of the valve mechanism (sphincter) in the bladder outlet and urethra. This may be due to intrinsic changes in the urethra, or loss of support and strength of the bladder neck and adjacent structures (pelvic relaxation, cystocele, pelvic organ prolapse). It is also associated with post surgical or radiation changes in men following treatment for prostate cancer. With physical exertion or activity that increases abdominal pressure, urine is forced through the deficient valve.
These two types of incontinence can be present separately or in combination. For this reason, proper evaluation is needed to direct appropriate therapy.
Another type of leakage is termed overflow incontinence. This results from failure of the bladder to empty either from intrinsic weakness, nerve injury or blockage to flow. With an overfull bladder, exertion or abdominal pressure can cause urine to spill out. Overflow incontinence can sometimes be confused with stress and urge incontinence. Proper evaluation and testing is necessary for correct diagnosis.
Other conditions such as urinary tract fistulae (holes between the urinary tract and other structures), stroke, spinal cord injury and other neurologic diseases can also cause incontinence and voiding problems.