Unilateral anal electrosensation. Modified technique to improve quantification of anal sensory loss

Anal electrosensation is usually tested by an annular configured electrode that stimulates the circumference of the anus. In certain pelvic conditions, the right and left pudendal nerve function may be damaged separately and to different degrees. This may only be detected by a unilateral electrode testing each side independently.

Our study compares accuracy and sensitivity of annular and unilateral electrodes in assessing patients with hemorrhoids, perineal descent, incontinence, after low anterior resection, and constipation (107 subjects).

In normal controls (n = 19), annular thresholds ranged from 0.5 to 2.7 mA and unilateral thresholds from 0.6 to 2.6 mA. In prolapsed hemorrhoids, unilateral was more sensitive than annular electrode in detecting deficits at the upper (P < 0.0001), mid (P < 0.005), and lower (P < 0.0005) anus. Patients with perineal descent had a sensory deficit in the upper anal canal, detected more consistently by unilateral electrode (P > 0.05). No significant abnormalities were found in neuropathic incontinence, after anterior resection and chronic constipation. Results of the unilateral electrosensory technique were found to be consistent with repeated measurements (r = 0.8878; P < 0.001).

By being more sensitive than the annular technique, the unilateral electrode method may become, with refinement, a useful test for quantifying anal sensation.