Rectal sensory evoked potentials: an assessment of their clinical value

To assess abnormalities of sensory conduction in anorectal disease we have evaluated peripheral sensory perception and somatosensory evoked potentials produced by rectal stimulation in control subjects and patients with either constipation or idiopathic faecal incontinence. Evoked potentials were also recorded after posterior tibial and dorsal genital nerve stimulation. Rectal sensation was also assessed using electrical stimulation. Reproducible evoked potential recordings after anorectal stimulation were possible in only a minority of subjects and when recorded showed intersubject and intrasubject variation. In the constipated group there was a significant difference in rectal electrical sensation (P < 0.05) from controls. We conclude that peripheral sensory testing demonstrates an abnormality in severe constipation. However, cerebral evoked potentials cannot be reliably recorded after rectal stimulation, and when recorded the latencies are of too broad a range to discriminate between health and disease. This probably relates to the difference between somatic and visceral pathways.