Purpose: This study was designed to evaluate the relationship between internal sphincter electromyographic frequency and ambulatory anal pressures in order to clarify the pathophysiology of internal anal sphincter dysfunction in fecal incontinence.
Methods: Seventy-two patients of median age 55 years (range, 24-75; 63 females) with neurogenic fecal incontinence and 33 normal subjects of median age 48.5 years (range, 25-74; 21 females) underwent fine-wire anal sphincter electromyography and anal manometry.
Results: The median internal anal sphincter electromyographic frequency was incontinent 0.25 Hz (0.2-0.34) and the control was 0.44 Hz (0.36-0.55; P < 0.03). Ambulatory resting pressures were incontinent median 54 cm of H2O (34-68 cm of H2O) and control 94 cm of H2O (72-102; P < 0.01). Internal sphincter electromyographic frequency correlated with anal resting pressures in both groups (P < 0.002). Internal sphincter electromyographic silence not attributable to electrode movement or the rectoanal inhibitory reflex, lasting 0.5 to 4 minutes occurred in all but two of the incontinent patients. The anal pressure during this period did not significantly change (P > 0.1). No recruitment of the external sphincter or puborectalis was noted during these episodes. Such electromechanical dissociation was not seen in the control group. The frequency of transient internal sphincter relaxation was 4 (ranges 2-6) per hour in controls and 8 (ranges, 6-12) per hour in incontinent patients (P < 0.01). Rectal pressures did not exceed midanal pressures in any of the controls but did in all of the incontinent patients on at least one occasion per hour in the incontinent group.
Conclusion: Internal anal sphincter activity exhibits electromechanical dissociation and relaxes abnormally in incontinent patients.