External anal sphincter dysfunction and postoperative bowel habits of patients with Hirschsprung's disease.

An electromyogram (EMG) of the external and sphincter (EAS) was obtained both before and after surgery in five patients with Hirschsprung's disease and eight normal control patients. The EMG, evoked by the transrectal stimulation of the pudendal nerve, was recorded at both the sacral and anal regions to investigate the deep and superficial EAS, respectively. In eight control patients, the EMG at the sacral region consisted of a polyphasic wave with apparently two or three major peaks, and the simple monophasic wave with one or two peaks was found at the anal region. Its peak corresponded to the early peaks in the sacral region. The mean onset latency of the EMG in the sacral region was 2.8 ms. Four patients with Hirschsprung's disease also exhibited responses that were similar to the controls, and their postoperative bowel habits were satisfactory. However, the remaining one patient, who still required a daily enema after surgery, exhibited an apparently different response, which was monophasic at both the sacral and anal regions with a long onset latency of 5.0 ms before and after surgery. It is postulated that some cases with Hirschsprung's disease might be associated with an EAS dysfunction before surgery, which possibly led to the development of postoperative bowel dysmotility.