The role of partial denervation of the puborectalis in idiopathic faecal incontinence.

Recent studies have suggested that patients with idiopathic faecal incontinence have neuropathic damage to the external and sphincter and pelvic floor musculature, though no direct assessment of puborectalis function has been made in intact man. Obstetric trauma and chronic straining at stool are thought to be possible causes for damage to the puborectalis nerve supply. In this study the motor unit potential duration in the external sphincter and puborectalis was measured by conventional electromyography in incontinent patients and two groups of continent patients who strained at stool. Our results confirm that incontinent patients had significant neuropathic damage to the puborectalis and the external sphincter compared with controls. Patients with the descending perineum syndrome, who were continent, showed partial denervation of the external sphincter and puborectalis, though the degree of abnormality in puborectalis was less than that in incontinent patients. Finally, patients with constipation showed neurogenic abnormalities in the external anal sphincter but not in the puborectalis. The findings suggest that partial denervation of the external sphincter can occur independently of partial denervation of the puborectalis in patients who strain at stool but if severe changes are present in both muscles, the patient is likely to be incontinent.