Pathophysiology & Diagnostic Tests
Fecal incontinence results when the pressure in the rectum exceeds anal sphincter pressure. Coughing or lifting can transiently increase intra-abdominal pressure and result in stool leakage if the sphincter is weak, and obesity may cause a chronic increase in intrarectal pressure. Forceful propulsion of stool into the rectum and/or loose stools may also overwhelm weak sphincter muscles as a result of infectious diarrhea or chronic conditions, such as irritable bowel syndrome (IBS). The strength of pelvic floor muscles can be affected by injuries to pelvic floor muscles, such as those sustained during childbirth, or by neurological disorders, such as diabetic neuropathy or spinal cord injury that affect the innervation of pelvic floor muscles. In addition, loss of the ability to perceive any increases in rectal pressure can result in a failure to contract pelvic floor muscles at appropriate times to prevent incontinence.
To state these pathophysiological observations more generally and in a way that provides a guide to diagnostic assessment, continence for stools depends on four main factors: rectal sensation, rectal storage capacity, anal sphincter strength and stool consistency. If any of these is compromised, FI can occur. The first three factors are dependent on the structural integrity and innervation of the rectum, anus and adjoining pelvic floor muscles, whereas stool consistency is determined by the motility (contractions) of the colon. In any one patient, multiple mechanisms may be involved so diagnostic evaluation should take all of these factors into account.
Standard diagnostic tests include anorectal manometry (pressure measurements in the anal canal and rectum) to assess pelvic floor muscle strength, rectal sensation and rectal compliance, and anal canal ultrasound to assess structural defects in the anal sphincters. Other diagnostic tests that may complement these standard tests include needle electromyography (EMG) or surface EMG of the anal canal, or pudendal nerve latency studies (pudendal nerve terminal motor latency) to assess the integrity of pudendal nerves innervating the pelvic floor. Pelvic MRI is sometimes substituted for anal canal ultrasound. These tests permit objective assessment and help to plan focused therapy. More detailed descriptions of the physiological mechanisms responsible for the maintenance of continence and the diagnostic tests used to determine which factors are important in a specific patient are available elsewhere.[7,37]
Women's Health. 2008;4(5):517-528. © 2008 Future Medicine Ltd.
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Cite this: Fecal Incontinence in Women: Causes and Treatment - Medscape - Sep 01, 2008.