The role of pelvic floor denervation in the aetiology of idiopathic faecal incontinence.

Weakness of the muscles of the pelvic floor and external anal sphincter may in theory be caused by a traction injury to the pelvic nerves incurred as a result of the excessive perineal descent that accompanies straining in the descending perineum syndrome (DPS). To investigate the role of this weakness in the aetiology of idiopathic faecal incontinence (IFI), measurements of perineal position, puborectalis mean fibre density (MFD), anal canal pressures, rectal sensation, capacity, and compliance were made in continent (DPS alone, n = 20) and incontinent (DPS + I, n = 19) patients with DPS, and a group of age and sex matched control subjects (n = 20). Perineal descent on straining was greater in DPS alone than in DPS + I. Puborectalis MFD was raised by similar degree in both DPS groups compared with the control subjects, and external anal sphincter function, assessed as voluntary squeeze pressure, was impaired by similar degree in DPS + I and DPS alone compared with the control subjects. Maximal basal anal canal pressure and rectal compliance were significantly reduced in DPS + I compared with DPS alone and the control subjects. Thus IFI did not result from progression of neurogenic muscle weakness, but occurred when there was also diminished internal anal sphincter tone and reduced rectal compliance.