The most common cause of bowel incontinence is damage to the muscles around the anus (anal sphincters). Vaginal childbirth can damage the anal sphincters or their nerves. That's why women are affected by bowel incontinence about twice as often as men.
Anal surgery can also damage the anal sphincters or nerves, leading to bowel incontinence.
There are many other potential causes of bowel incontinence, including:
Cognitive (thinking) impairment (such as after a stroke or advanced Alzheimer's disease)
More than one cause for bowel incontinence is frequently present. It's also not unusual for bowel incontinence to occur without a clear cause.
Diagnosis of Bowel Incontinence
Discussing bowel incontinence may be embarrassing, but it can provide clues for a doctor to help make the diagnosis. During a physical examination, a doctor may check the strength of the anal sphincter muscle using a gloved finger inserted into the rectum.
Other tests may be helpful in identifying the cause of bowel incontinence, such as:
Stool testing. If diarrhea is present, stool testing may identify an infection or other cause.
Endoscopy. A tube with a camera on its tip is inserted into the anus. This identifies any potential problems in the anal canal or colon. A short, rigid tube (anoscopy) or a longer, flexible tube (sigmoidoscopy or colonoscopy) may be used.
Anorectal manometry. A pressure monitor is inserted into the anus and rectum. This allows measurement of the strength of the sphincter muscles.
Endosonography. An ultrasound probe is inserted into the anus. This produces images that can help identify problems in the anal and rectal walls.
Nerve tests. These tests measure the responsiveness of the nerves controlling the sphincter muscles. They can detect nerve damage that can cause bowel incontinence.
MRI defecography. Magnetic resonance imaging of the pelvis can be performed, potentially while a person moves her bowels on a special commode. This can provide information about the muscles and supporting structures in the anus, rectum, and pelvis.