EVIDENCE OF ELECTROMECHANICAL DISSOCIATION OF THE INTERNAL ANAL-SPHINCTER IN IDIOPATHIC FECAL INCONTINENCE

PURPOSE: This study was designed to evaluate the relationship between internal sphincter electromyographic frequency and ambulatory anal pre ssures in order to clarify the pathophysiology of internal anal sphinc ter dysfunction in fecal incontinence. METHODS: Seventy two patients o f 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 elect romyographic frequency was incontinent 0.25 Hz (0.2-0.34) and the cont rol was 0.44 Hz (0.36-0.55; P < 0.03). Ambulatory resting pressures we re 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 frequ ency correlated with anal resting pressures in both groups (P < 0.002) . Internal sphincter electromyographic silence not attributable to ele ctrode movement or the rectoanal inhibitory reflex, lasting 0.5 to 4 m inutes occurred in all but two of the incontinent patients. The anal p ressure 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 t he control group. The frequency of transient internal sphincter relaxa tion 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 exce ed midanal pressures in any of the controls but did in all of the inco ntinent patients on at least one occasion per hour in the incontinent group. CONCLUSION: Internal anal sphincter activity exhibits electrome chanical dissociation and relaxes abnormally in incontinent patients.