Primary degeneration of the internal anal sphincter as a cause of passive faecal incontinence

Lancet. 1997 Mar 1;349(9052):612-5. doi: 10.1016/S0140-6736(96)09188-X.


Background: Faecal incontinence is usually attributed to pelvic-floor denervation of striated muscle or direct sphincter trauma. We have identified a cause of passive faecal incontinence related to degeneration of the internal anal sphincter smooth muscle, in the absence of denervation, structural damage, external-sphincter weakness, or sensory abnormalities.

Methods: Patients were included on the basis of: passive faecal incontinence, no urge faecal incontinence, low anal pressure whilst at rest, normal anal-squeeze pressure, endosonographically confirmed circumferentially intact internal and external anal sphincters, and normal pudendal nerve terminal nerve latencies. In a second analysis done to assess the proportion of patients with this disorder, we recorded the cause of incontinence in consecutive patients seen during a 6-month period.

Findings: 45 patients (35 women, median age 63 years, range 23-80 years) fulfilled the diagnostic criteria. Median duration of symptoms was 2 years (3 months to 20 years). Nine of the 35 women were nulliparous. The median resting anal pressure was 40 cm water (16-56 cm water, normal > 60 cm water). Endosonography revealed an internal sphincter that was thin and hyperechogenic, and had a poorly defined edge. The normal increase in the thickness of the internal anal sphincter with 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 smooth muscle is a discrete clinical condition causing passive faecal incontinence.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Anal Canal / diagnostic imaging
  • Anal Canal / pathology*
  • Fecal Incontinence / diagnostic imaging
  • Fecal Incontinence / etiology*
  • Fecal Incontinence / pathology
  • Female
  • Humans
  • Middle Aged
  • Ultrasonography