'Objective' assessment of rectal sensation: a novel approach

Rectal sensation is used as an investigative tool in the diagnosis of anorectal pathology. However, the data obtained are subjective depending on the patient's perception of the sensation. We investigated the hypothesis that sympathetic skin response (SSR) can be used as a tool for objective assessment of the rectal sensation. The SSR was recorded in 24 healthy volunteers (age 37.2 years, 14 men) using a surface electrode applied to the skin of the palmar surface of the subject's hand and a reference electrode to the dorsum of the same hand. The EMG activity of the pelvic floor muscles was registered by a surface electrode fixed to the perineal skin. The subject was asked before and after individual anesthetization of the rectum and palm to report the first rectal and urge sensations during balloon filling of the rectum in increments of 10 ml of saline. Low volume rectal distension effected no sympathetic skin or pelvic floor responses, while larger volumes produced the response. The skin and pelvic floor responses occurred with every rectal sensation and corresponded with the volunteers' subjective perception. Urge suppression was associated with synchronous decrease of skin and pelvic floor responses which disappeared on balloon expulsion. Rectal balloon distension, 20 minutes after individual anesthetization of the rectum or palm produced no palm skin response, which returned however 3 hours later. A novel approach which can objectively define subjective perceptions arising from the rectum has been identified. Rectal sensations produce coordinated sympathetic skin response and pelvic floor activity which seem to be mediated through a reflex which we term the "recto-palmar reflex". Further studies are required to investigate the role of this reflex in defection and sympathetic disorders.