Increased motor unit fibre density in the external anal sphincter muscle in ano-rectal incontinence: a single fibre EMG study.

The motor unit fibre density in the external anal sphincter muscle has been measured in 13 normal subjects aged 18 to 78 years, and in 14 patients with ano-rectal incontinence, aged 17 to 72 years. The mean fibre density in the normal subjects was 1.5 +/- 0.16, and in the incontinent subjects it was 2.17 +/- 0.28 (p less than 0.001). These findings provide support for the suggestion that ano-rectal incontinence commonly has a neurogenic basis.