Urge incontinence is due to an overactive bladder in which the bladder muscle contracts without your permission and you urinate involuntarily. This type of incontinence is often associated with urinary frequency. The bladder and urethra are made of a type of muscle called smooth muscle, so named because of the smooth appearance under the microscope (as opposed to skeletal muscle which has a striated (striped) appearance). Smooth muscle carries out functions of the body that you don’t have to think about such as stomach, bowel or bladder function. Urge incontinence can occur in situations where the bladder receives too many signals to contract such as with Parkinson’s Disease or Multiple Sclerosis. It can also occur in spinal problems like stenosis (narrowing of the canal) or a herniated disk, both of which irritate the spine by compressing the nerves.
In other instances, the bladder reacts to having to work harder than usual to empty and “gets angry” such that any time the bladder is filled enough to trigger the urge to go, it goes. This can occur when the outlet of the bladder is obstructed such as with prolapse (organs falling down), or overly aggressive incontinence surgery. With prolapse, the urethra becomes folded over itself because the bladder has fallen to or outside the vaginal opening which creates a kink in the urethra. This happens because the urethra opening is fixed to the skin and can’t move with the bladder. A high pressure is created in the urethra that the bladder muscle must overcome to get the water out. High pressure in the urethra from prolapse can also occur when the rectum falls (rectocele) and pushes up against the urethra from the underside (think of placing one’s finger in the vagina and pressing the urethra shut).
In some cases, prior incontinence surgery elevates the urethra a little too high such that the water must travel uphill through a urethra compressed to a degree to get out. Other times the incontinence surgery is just fine but the bladder hasn’t adjusted to the slight increase in outlet resistance. Sort of like bridling a wild horse makes it a little irritated. In other cases, the incontinence surgery is fine, but the bladder has started to fall (cystocele) and now there is a mismatch of support which creates a kinking effect in the urethra. Less commonly there is a condition in which the bladder is irritated by a foreign body like a stone, a stitch, or a cancer. In many cases no apparent cause can be determined and the bladder is just hyperactive.
Treatments are geared toward eliminating the underlying cause if possible. This may entail surgery or a pessary to address prolapse and relieve the kinking or compressive effect on the urethra. Sometimes it requires undoing or redoing an incontinence surgery. If the cause has been corrected and the urge incontinence continues, or a cause cannot be found or treated we try to harness the hyperactivity of the bladder muscle itself. This can be done with medications to relax the smooth muscle of the bladder (similar to the way valium is given to treat back muscle spasm). A great compliment to this treatment is to enhance the effectiveness of our “potty training reflex” by strengthening our pelvic floor muscles. Pelvic floor physical therapy helps with urge incontinence by engaging a spinal reflex and physically closing the urethra to hold the urine in the bladder when the urge hits. The contraction of the pelvic floor muscles triggers a signal to the spine which in turn sends a signal to the bladder telling it to relax. The more effectively you can contract your pelvic floor muscles the more efficient the reflex becomes and the more control you have over urge incontinence. In stubborn cases a stimulator (like a pacemaker) may be implanted to help subdue the bladder. This device (Interstim®) sends signals along the pelvic nerves to the bladder which causes it to relax, having an effect similar to the “potty training reflex”. Other treatments have included injecting Botox® into the bladder to paralyze some of the muscle, which can be effective but must be repeated. Severe cases may be treated by sewing some bowel onto the bladder to increase the capacity.