PRIMARY DEGENERATION OF THE INTERNAL ANAL-SPHINCTER AS A CAUSE OF PASSIVE FECAL INCONTINENCE

Background Faecal incontinence is usually attributed to pelvic-floor d enervation of striated muscle or direct sphincter trauma. We have iden tified a cause of passive faecal incontinence related to degeneration of the internal anal sphincter smooth muscle, in the absence of denerv ation, structural damage, external-sphincter weakness, or sensory abno rmalities. Methods Patients were included on the basis of: passive fae cal incontinence, no urge faecal incontinence, low anal pressure whils t at rest, normal anal-squeeze pressure, endosonographically confirmed circumferentially intact internal and external anal sphincters, and n ormal pudendal nerve terminal nerve latencies. In a second analysis do ne to assess the proportion of patients with this disorder, we recorde d the cause of incontinence in consecutive patients seen during a 6-mo nth period. Findings 45 patients (35 women, median age 63 years, range 23-80 years) fulfilled the diagnostic criteria. Median duration of sy mptoms was 2 years (3 months to 20 years). Nine of the 35 women were n ulliparous. The median resting anal pressure was 40 cm water (16-56 cm water, normal >60 cm water). Endosonography revealed an internal sphi ncter that was thin and hyperechogenic, and had a poorly defined edge. The normal increase in the thickness of the internal anal sphincter w ith age was not seen, Anal-squeeze pressure, sensitivity, and pudendal nerve latencies were normal. In the second analysis the condition was identified in eight of 230 patients, representing 4% of new referrals . Interpretation Primary degeneration of the internal anal sphincter s mooth muscle is a discrete clinical condition causing passive faecal i ncontinence.