Discrimination is not impaired by excision of the anal transition zone after restorative proctocolectomy

Anal sensation has been assessed using a constant current stimulator in 21 patients after restorative proctocolectomy (15 J pouch, 6 W pouch). The anal transition zone (ATZ) has been excised in 15 patients but preserved in 6. Results were compared with 14 age- and sex-matched patients with ulcerative colitis (UC) and 14 controls. Median threshold values in the lower, mid and upper zones of the anal canal in pouch patients were: 6.8 mA, greater than 15.0 mA and greater than 15.0 mA respectively compared with 3.9 mA (P less than 0.01), 5.7 mA (P less than 0.01) and 11.4 mA (P less than 0.01) in UC and 3.5 mA (P less than 0.01), 4.2 mA (P less than 0.01) and 11.4 mA (P less than 0.01) in controls. The mid and upper zone threshold anal sensation was significantly lower when the ATZ had not been removed and except in the lower zone did not differ from UC or controls (median threshold sensations when ATZ was preserved were: lower zone, 5.8 mA; mid zone, 5.5 mA; upper zone, 7.5 mA). Paired studies in eight patients showed that excision of the ATZ was associated with a significant impairment in anal sensation (mid zone: 5.7 versus greater than 15.0 mA, P less than 0.05; upper zone: 7.5 versus greater than 15.0 mA, P less than 0.05) whereas no change in anal sensation was recorded when the ATZ was preserved. Despite these physiological changes, no clinical benefit could be identified in patients in whom the ATZ was preserved. Discrimination was normal in all except one patient. The incidence of soiling, nocturnal incontinence and failure to defer defaecation for more than 1 h was recorded in 3/15 patients (20 per cent) whose ATZ had been removed, compared with 1/6 patients (17 per cent) in whom the ATZ had been preserved. We conclude that excision of the ATZ does not eliminate the ability to discriminate and does not increase the risk of impaired continence after ileo-pouch anal anastomosis.