Anal sphincteric neurogenic injury in asymptomatic nulliparous women and fecal incontinence.

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 ± 5 yr; mean ± SE) and 20 women with FI (54 ± 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 = 0.04) and polyphasic MUP (2 controls, 9 patients, P = 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 (κ statistic 0.63 ± 95% CI: 0.32-0.96). Anal resting and squeeze pressures were lower (P ≤ 0.01) in FI than controls. Anal sphincter neurogenic or muscle injury assessed by needle EMG was associated (P = 0.01) with weaker squeeze pressures (83 ± 10 mmHg vs. 154 ± 30 mmHg) and explained 19% (P = 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.