Neurophysiologic assessment of the anal sphincters.
One hundred twenty consecutive patients with either fecal incontinence (60 patients), chronic constipation (41 patients), or idiopathic intractable pelvic pain (19 patients) were prospectively assessed. Patients underwent concentric needle electromyography (EMG), bilateral pudendal nerve terminal motor latency evaluation, anorectal manometry, and cinedefecography. The most common EMG finding in patients with fecal incontinence was decreased recruitment of motor units with squeezing and polyphasic motor unit potentials; these are consistent with an injury pattern. The most common EMG finding in the constipated patients was paradoxical puborectalis contraction. This latter abnormality was also a frequent finding in patients with rectal pain, as was prolongation of pudendal nerve latency. Paradoxical puborectalis contraction was diagnosed more frequently with EMG than with cinedefecography. Inter-examination correlation was best in the incontinent group between EMG and manometry. Cinedefecography had poor correlation with EMG in all patient groups but was valuable in the detection of additional pathology such as rectoanal intussusception and anterior rectocele. Electromyography including pudendal nerve terminal motor latency assessment is a valuable adjunct in the evaluation of disorders of evacuation. The information it yields is complementary to that offered by more routine physiologic examinations.