Outcome measures for fecal incontinence: anorectal structure and function.
Fecal incontinence is a symptom attributable to a variety of disorders affecting one or more factors that maintain continence. Objective assessments should complement symptom assessments as outcome measures in therapeutic trials; conceivably, these assessments may also predict the response to therapy. Consistent with existing trends, most therapeutic trials should incorporate anal sphincter pressures and rectal sensation as outcome variables, paying meticulous attention to techniques. Rectal sensation is increased after pelvic floor retraining by biofeedback therapy in fecal incontinence; however, the predictive value of improved anal pressures after biofeedback has not been clearly established. Other factors maintaining continence can be assessed by newer approaches. In addition to assessing rectal sensation, a barostat also measures rectal compliance; alterations in rectal compliance modulate rectal perception. Particularly appropriate end points for trials involving surgical repair are sphincter integrity, assessed by endoanal ultrasound or magnetic resonance imaging (MRI), and puborectalis and pelvic floor motion, assessed by dynamic MRI. Despite disagreement about which technique is superior for evaluating the internal sphincter, MRI performs the same or better than ultrasound for assessing the external sphincter. The utility of measuring pudendal nerve latencies as a marker of pudendal nerve injury is limited; needle electromyography provides a sensitive measure of denervation and can usually identify myopathic damage, neurogenic damage, or mixed injury. These standardized, reproducible assessments of the multifaceted mechanisms maintaining fecal incontinence should be incorporated as outcome variables in therapeutic trials of fecal incontinence.