Differences in anal sensation in continent and incontinent patients with perineal descent

Neuropathic damage secondary to pelvic floor descent is considered to be an important aetiological factor in idiopathic faecal incontinence. Perineal descent however does not necessarily result in a loss of motor function or incontinence. To elucidate the role of anal sensation in the continence mechanism we measured mucosal electrosensitivity and thermal sensitivity in normal controls and in both continent and incontinent patients with perineal descent. A catheter carrying two platinum electrodes was used to assess mucosal electrosensitivity and a water perfused thermode 1 cm long to measure thermal sensory thresholds. In addition, routine anal manometry was performed. The degree of perineal descent and anorectal angle was assessed radiographically. Anal sensation was largely preserved in continent patients with perineal descent (Controls vs continent perineal descent, Mucosal electrosensitivity (ma), lower anal canal: 4 (2-7) vs 5 (2.6-8) ns; middle anal canal 4 (2-7) vs 4.2 (2-15) ns; upper anal canal 6.5 (4-13) vs 8.3 (3.6-16) p less than 0.05, thermal sensitivity, median threshold (degrees C), lower anal canal 0.92 (0.5-2.5) vs 0.95 (0.3-3.6) ns; middle anal canal 0.83 (0.4-1.5) vs 0.75 (0.2-2) ns; upper anal canal 0.98 (0.6-2.4) vs 2.2 (0.5-4.8) p less than 0.05). There was a severe impairment of anal sensation in the incontinent patients with perineal descent despite a greater degree of perineal descent in the continent group. Loss of anal sensation is associated with the development of incontinence and is likely to be involved in the pathogenesis of the condition.