The muscles in your anus are unique in their ability to distinguish among solid, liquid and gas. They also must contract to keep you continent when you are asleep and relax when the rest of you is straining to empty the bowel. In the elderly, sensation is less reliable around the anus, and stool can soil underwear.
There is a mass movement of feces into the rectum after eating, usually after breakfast with the gastro-colic reflex. The only gut sensation we feel is rectal distension, originating in the rectum, the pelvic floor or both, and it may decrease with age. Sitting on the toilet causes the urge to push and increases intra-abdominal pressure, initiating sphincter relaxation, reducing the angle of the rectum to the colon, and causing defecation.
There are four continence-maintaining mechanisms:
- A muscular sling (of the pelvic floor muscles) attached to the front of the pelvis closing the rectal lumen by an acute bend to the colon.
- A two-part sphincter or purse-string closure. The first internal sphincter continues the gut muscle and works involuntarily for resting closure. Below, the external sphincter is a voluntarily controlled body muscle for emergency anal closure when coughing or sneezing.
- The blood vessels and bowel-lining cells contribute a seal.
- The upper half of the anal canal acts as a flutter valve.
The most common cause of incontinence in nursing homes (60%) is constipation and fecal wedging (impaction). In some elderly persons, aging results in reduced anal sensation and lower sphincter pressures, and the rectal angle is straighter. Incontinent patients are less mobile. Another cause is global brain disease, in which the reflexes are ignored and the body takes over and flushes itself automatically. A third cause is associated with local colon or rectal disease such as diarrhea, cancer, diabetes, diverticula (multiple abnormal pouches or sacs opening from the colon), inflammatory bowel disease or overuse of laxatives. Finally, when the anal muscles are weak (causing an open, expanded anus), stool in the rectum cannot be held for convenient evacuation, and it escapes.
Management of constipation with impaction includes enema or laxative emptying with induced constipation and planned twice-weekly laxatives or enema emptying. An exercise regimen is helpful. Other forms of incontinence benefit from pelvic floor exercise monitored by biofeedback.
Anal incontinence – which occurs most frequently in older patients -- can be a difficult condition. But treatments are available, with good rates of success, and your doctor will work with you to find a therapy that is effective for you.
To make an appointment with a Washington University colorectal surgeon, please call (314) 454-7177.