Studies on anal canal sensitivity in patients with or without soiling after low anterior resection for lower rectal cancer

Background/Aims: Anal canal sensitivity is conducted by the sensory branch of the pudendal nerve. To clarify the significance of the anal canal sensitivity function in patients with soiling after low anterior resection (LAR) for lower rectal cancer, we studied the threshold of anal canal sensitivity using an anal canal sensitivity test (ACST). Materials: Subjects were 23 patients, 15 men and 8 women aged 47-69 years with a mean age of 63.3 yr, divided into patients with soiling (n=10) and patients without soiling (n=13), compared with control subjects (n=20; 12 men and 8 women aged 4065 yr with a mean age of 55.6 yr). These subjects had undergone LAR at least 12-13 months (mean 12.8 months) previously, and had no preoperative or postoperative complications. Methods: Anal canal sensitivity was measured using an ACST. Measurement points of the anal canal were divided into 2 sites: the portion just on the dentate line (DL) and the portion 1cm below the DL. A small electric current from a constant current generator was passed between the electrodes until the patients felt a sensation often described as tingling or pulsing. The threshold of sensitivity was assessed in the upper, middle, and lower parts of the anal canal. Results: In control subjects, recording at the DL site showed the best results. Anal canal sensitivity in patients with soiling was significantly lower than in patients without soiling at both sites (p<0.0001). There were no significant differences at the site 1cm below the DL among patients with soiling and patients without soiling. Patients with soiling showed the worst results in anal canal sensitivity at the DL. Conclusion: The ACST shows significantly lower sensitivity in the anal canal site of DL in patients with soiling after LAR. These findings suggest that soiling after LAR may be due to damage to the pudendal sensory nerves.