Anal sphincteric neurogenic injury in asymptomatic nulliparous women and fecal incontinence

Abstract

Bharucha AE, Daube J, Litchy W, Traue J, Edge J, Enck P, Zinsmeister AR. Anal sphincteric neurogenic injury in asymptomatic nulliparous women and fecal incontinence. Am J Physiol Gastrointest Liver Physiol 303: G256 -G262, 2012. First published May 4, 2012 doi:10.1152/ajpgi.00099.2012.-While anal sphincter neurogenic injury documented by needle electromyography (EMG) has been implicated to cause fecal incontinence (FI), most studies have been uncontrolled. Normal values and the effects of age on anal sphincter motor unit potentials (MUP) are ill defined. The functional significance of anal sphincter neurogenic injury in FI is unclear. Anal pressures and EMG were assessed in 20 asymptomatic nulliparous women (age, 38 Ϯ 5 yr; mean Ϯ SE) and 20 women with FI (54 Ϯ 3 yr). A computerized program quantified MUP duration and phases. These parameters and MUP recruitment were also semiquantitatively assessed by experienced electromyographers in real time. Increasing age was associated with longer and more polyphasic MUP in nulliparous women by quantitative analysis. A higher proportion of FI patients had prolonged (1 control, 7 patients, P ϭ 0.04) and polyphasic MUP (2 controls, 9 patients, P ϭ 0.03) at rest but not during squeeze. Semiquantitative analyses identified neurogenic or muscle injury in the anal sphincter (11 patients) and other lumbosacral muscles (4 patients). There was substantial agreement between quantitative and semiquantitative analyses ( statistic 0.63 Ϯ 95% CI: 0.32-0.96). Anal resting and squeeze pressures were lower (P Յ 0.01) in FI than controls. Anal sphincter neurogenic or muscle injury assessed by needle EMG was associated (P ϭ 0.01) with weaker squeeze pressures (83 Ϯ 10 mmHg vs. 154 Ϯ 30 mmHg) and explained 19% (P ϭ 0.01) of the variation in squeeze pressure. Anal sphincter MUP are longer and more polyphasic in older than younger nulliparous women. Women with FI have more severe neurogenic or muscle anal sphincter injury, which is associated with lower squeeze pressures. aging; electromyography; pudendal neuropathy INITIALLY DOCUMENTED BY HISTOLOGICAL evidence of sphincter denervation (27), the concept that pudendal nerve injury contributes to anal weakness in fecal incontinence (FI) gained traction when prolonged pudendal nerve terminal motor latencies were documented in FI and after obstetric anal sphincter injury (2, 22, 30). However, prolonged pudendal nerve latencies are flawed markers of pudendal nerve function (13). Hence, needle electromyography (EMG) is the only technique that can reliably identify anal sphincter neurogenic injury that can result from damage to the sacral spinal cord, cauda equina, S2-4 spinal nerves, the pudendal nerve, or its branches as they enter the anal sphincter (28,29,34). Anal sphincter EMG can also identify local muscle trauma (3). However, anal sphincter EMG is not widely available and infrequently used, mainly when neurogenic injury is suspected, in clinical practice. Also, based on limited data that suggest that anal sphincter denervation predicts poore...

An Update on Anorectal Disorders for Gastroenterologists

“…Hence, needle electromyography is the only established technique for identifying anal neurogenic injury. A recent controlled study observed neurogenic or muscle injury in 55% of a selected cohort of 20 women with FI, which is comparable to that reported previously 58 . Moreover, even in asymptomatic nulliparous women, increased age was associated with neurogenic injury, which partly explained weak squeeze pressures.…”

Anorectal Disorders

“…7 Needle EMG can identify normal, neurogenic, or muscle injury. 57,104 Recently, prolonged rectal and anal motor evoked potentials have been shown in a majority of FI patients, suggesting that neurophysiologic dysfunction plays an important role. 105 …”

Epidemiology, Pathophysiology, and Classification of Fecal Incontinence: State of the Science Summary for the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) Workshop

“…Constipation with fecal impaction is a significant risk in nursing homes (20, 81). Cross-sectional studies suggest that age is associated with alterations in anorectal functions (i.e., lower anal resting and squeeze pressures, anal sphincter denervation, increased rectal compliance, and decreased rectal sensation) (82–85). These changes may predispose to FI.…”

“…The association between sphincter injury documented by imaging and weakness is incompletely understood. Neurogenic lesions can occur at any level of the axis extending from the central nervous system to the external anal sphincter (85). The most common causes of neurogenic injury include a peripheral neuropathy (e.g., due to diabetes mellitus), pudendal nerve stretch injury, or obstetric injury.…”

“…The most common causes of neurogenic injury include a peripheral neuropathy (e.g., due to diabetes mellitus), pudendal nerve stretch injury, or obstetric injury. Moreover, recent studies suggest that even asymptomatic older nulliparous women have anal sphincter neurogenic injury, which partly explained weak squeeze pressures (85). Since needle EMG is the only available technique for documenting neurogenic injury, newer, and preferably less invasive approaches are necessary (95).…”