Neurophysiological assessment of the pelvic floor.

The improbable marriage of neurophysiology to proctology has proved highly profitable in that the two disciplines have combined to study clinical areas in common, to the mutual benefit of each. The starting point has been anorectal incontinence, but later the emphasis has been extended to include other functional disorders such as constipation. Gowers could be described as the first physiologist to display scientific interest in anal canal function and was the first to describe the rectoanal inhibitory reflex.' Reflex responses affecting the internal anal sphincter were later studied in more detail by Denny Brown and Robertson2 and the first studies of external anal sphincter function were by Beck3 and Floyd and Walls.4 Interest in the anal sphincter by non-clinicians virtually ceases at this point. Clinical contributions to anal sphincter function were made by Kerremans,s Schuster,6 Frencker and Euler7 who largely used manometric techniques. Such methods are relatively crude and are largely restricted to determining smooth muscle activity, that is to say internal anal sphincter function. Investigation of the striated component using conventional electromyographic techniques, showed that these muscles are tonically active at rest and during sleep4 and contraction is reflexly evoked by coughing, sneezing or lifting heavy weights.8 Such activity is facilitated by means of a spinal reflex arc' and as such is maintained in paraplegics if the level of cord section is above S2. Porter'0 was able to show that in patients with rectal prolapse the conventional EMG was abnormal, in that action potentials were of low voltage and there was a poor interference pattern during periods of attempted voluntary contraction. The interpretation of these observations was possible thanks to the combination of a proctologist, a neurophysiologist, and a neuropathologist who showed evidence of denervation in the pelvic floor muscle biopsies of patients with faecal incontinence and rectal prolapse using elegant enzyme histochemistry." The technique required visual assessment of the muscle under the microscope, however, and was open to observer error. An objective assessment of the innervation of the pelvic floor was then approached by studying the latency of the anal reflex in response to electrical stimulation of the perianal skin.'2 This method often produced paradoxical results, however, because of the suprasegmental nature of the reflex. A much more satisfactory approach to objective investigation of somatic muscle function has been by single fibre EMG.'3 The technique can be adapted to the study of pelvic floor musculature and has unequivocably …