Anal sensitivity test: what does it measure and do we need it? Cause or derivative of anorectal complaints

This study was undertaken to determine the anal sensitivity in controls and in different patient groups and to establish factors that determine anal sensitivity.

Anorectal function tests were performed in 387 patients with different anorectal diseases. Anal sensitivity was measured in 36 controls. Anal sensitivity was measured by means of mucosal electrosensitivity (MES) using a catheter with two electrodes placed in the anal canal. A constant current (square wave stimuli 100 microsec, pulses per second) was increased stepwise from 1 to 20 mAmp until the threshold sensation was reached. Other tests used were anal manometry (maximum basal pressure, maximum squeeze pressure, rectal compliance (maximum rectal volume and pressure), endosonography (submucosal thickness), defects and thickness of internal and external sphincter), electromyography (maximum contraction pattern, Grade 1 (solitary contractions) to Grade 4 (interference pattern)), and pudendal nerve terminal motor latency. Multiple regression analysis was performed. It was postulated that age, local conditions (anal scars, anal fissures, hemorrhoids, mucosal prolapse, proctitis, sphincter thickness and defects, and submucosal thickness), and neurologic factors could influence anal sensitivity.

Controls had an MES of 3.4 +/- 1.7. MES was significantly increased compared with controls in patients with fecal incontinence, soiling, hemorrhoids, mucosal prolapse, constipation, anal scars, anal surgery, and sphincter defects; patients with fecal incontinence had the highest MES (6.7 +/- 4.3; P < 0.0001). Patients with anal fissures and proctitis showed no differences compared with controls. MES correlated significantly with age (R = 0.29), maximum basal pressure (R = -0.29), maximum squeeze pressure (R = -0.32), submucosal thickness (R = 0.19), maximum contraction pattern (R = -0.39), single-fiber electromyography (R = 0.39), and maximum rectal volume and pressure (0.14). Multiple regression analysis showed that age, internal sphincter defects, and submucosal thickness significantly influenced anal sensitivity, but explained only 10 percent of the variance.

Anal sensitivity is diminished in all patients with anorectal diseases except for anal fissures and proctitis. There are correlations with other anorectal function tests. Anal sensitivity is determined for 10 percent by age, internal sphincter defects, and thickness of the submucosa. Anal sensitivity measurement, therefore, has limited clinical value and should be used in conjunction with other tests in a research setting.