Idiopathic (primary neurogenic) fecal incontinence results from denervation of both the anal sphincter and pelvic ﬂoor muscles. Denervation injury related to obstetric trauma accounts for approximately three of four cases of idiopathic fecal incontinence and is the most common overall cause of fecal incontinence (70,71).
Obstetric Trauma The two proposed mechanisms of pudendal neuropathy are stretch injury during the second stage of labor and compression of the nerve as it exits Alcock’s canal (70).
Established risk factors for pelvic ﬂoor neuropathy include multiparity, high birth weight, forceps delivery, prolonged active second stage, and third-degree laceration (72,73). Several studies have shown increased pudendal nerve terminal motor latencies following vaginal delivery, especially after sphincter laceration (53,71,74). Most women will recover function within a few months postpartum. Others will have evidence of injury several years later, which may represent the cumulative effects of subsequent deliveries (71,75). However, fecal incontinence will develop in only a fraction of patients with neuropathy (73).
Descending Perineum Syndrome As noted previously, prolonged straining for any reason could cause descending perineum syndrome. This syndrome is defined as descent of the perineum beyond the ischial tuberosities during Valsalva (38,39). Pudendal neuropathy results from stretching and entrapment of the pudendal nerve. This diagnosis is supported by findings of elongation of the pudendal nerve, prolonged pudendal nerve motor terminal latency, and decreased anal sensation in women with perineal descent (76–78). As pudendal neuropathy progresses, it ultimately leads to fecal incontinence (40,79).
Functional Fecal Incontinence The Rome III criteria established well-defined guidelines for functional causes of fecal incontinence (Table 28.7). The criteria essentially exclude systemic and anatomic abnormalities; however, minor abnormalities of sphincter innervation or structure are permitted.
Irritable Bowel Syndrome The diarrhea variant of irritable bowel syndrome is often associated with fecal incontinence as well as disordered defecation. The criteria for diagnosis are presented in Table 28.4.
Functional Diarrhea The Rome III criteria create a unifying definition of diarrhea called functional diarrhea (Table 28.8). The rationale for the criteria listed in Table 28.8 stems from the variability in patients’ descriptions of diarrhea (46).
Table 28.7 Functional Fecal Incontinence 1. Recurrent uncontrolled passage of fecal material in an individual with a developmental age of at least 4 years and one or more of the following: a.
Abnormal functioning of normally innervated and structurally intact muscles b.
Minor abnormalities of sphincter structure and/or innervation c.
Normal or disordered bowel habits, (i.e., fecal retention or diarrhea) d.
2. Exclusion of all of the following a.
Abnormal innervation caused by lesion(s) within the brain (e.g., dementia), spinal cord, or sacral nerve roots, or mixed lesions (e.g., multiple sclerosis), or as part of a generalized peripheral or autonomic neuropathy (e.g., due to diabetes) b.
Anal sphincter abnormalities associated with a multisystem disease (e.g., scleroderma) c.
Structural or neurogenic abnormalities believed to be the major or primary cause of fecal incontinence.