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ANAL INCONTINENCE

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Although definitions are inconsistent, anal incontinence (AI) is most commonly defined as an involuntary loss of flatus, liquid, or solid stool that causes a social or hygienic problem (Abrams, 2005; Haylen, 2010). The definition of AI includes incontinence of flatus, whereas that of fecal incontinence (FI) does not.

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Despite acceptance of these by healthcare professionals, one survey observed that only 30 percent of nearly 1100 community-dwelling women with FI had heard the term “fecal incontinence,” and 71 percent preferred the term “accidental bowel leakage” (Brown, 2012). Thus, at a recent consensus workshop, this latter more patient-centered term was suggested for use with patients (Bharucha, 2015).

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AI can lead to poor self-image and isolation, and the social and quality-of-life effects of AI are significant (Johanson, 1996). Additionally, AI increases the likelihood that an older patient will be admitted to a nursing home rather than cared for at home (Grover, 2010).

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Epidemiology

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Anal incontinence is common, and rates among men and women are similar (Madoff, 2004b; Nelson, 2004). In one National Health and Nutrition Examination Survey (NHANES), FI was also not significantly associated with race or ethnicity, education level, income, or marital status (Whitehead, 2009). Although all age groups may be affected, the AI prevalence increases with age and may reach 46 percent in older, institutionalized women (Nelson, 1998). Using data from NHANES that incorporated years 2005 through 2010, investigators noted that the prevalence of FI in women approximated 9 percent (Nygaard, 2008; Wu, 2014). Similarly, the estimated prevalence of FI in noninstitutionalized U.S. adults was 8.3 percent (18 million). Of these individuals, liquid stool incontinence was noted in 6.2 percent, mucus in 3.1 percent, and solid stool in 1.6 percent (Whitehead, 2009). The prevalence of FI increased from 2.6 percent in those aged 20 to 30 years and rose to 15.3 percent in subjects aged 70 years or older.

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Physiology

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Normal defecation and anal continence are complex processes that require: (1) a competent anal sphincter complex, (2) normal anorectal sensation, (3) adequate rectal capacity and compliance, and (4) conscious control. Logically, mechanisms responsible for FI include anal sphincter and pelvic floor weakness, reduced or increased rectal sensation, reduced rectal capacity and compliance, and diarrhea (Bharucha, 2015). In many patients these factors may be additive, and thus no single physiologic measure is consistently associated with FI.

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Muscular Contributions
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Essential contributors to fecal continence include the internal and external anal sphincters and the puborectalis muscle (Figs. 38-9 and 38-21). Of these, the internal anal sphincter (IAS) is the thickened distal 3- to 4-cm longitudinal extension of the colon’s circular smooth-muscle layer. It is innervated by the autonomic nervous system and ...

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