Physiological Studies on the Pudendal Nerve Function in Patients after Low Anterior Resection for Rectal Cancer

Seigo Igarashi, Ryouichi Tomita and Masahiro Fukuzawa*

First Department of Surgery, Nihon University School of Medicine
Department of Pediatric Surgery, Osaka University, Graduate School of Medicine*

Aim: To clarify the significance of the roles of the pudendal motor and sensory nerves contribute to involuntary defecation (soiling) in patients following low anterior resection (LAR) for rectal cancer, we studied the motor latency and sensory function of the pudendal nerves. Materials: Subjects were 28 patients 19 men and 9 women aged 47 to 77 years (mean: 65.4 years) divided into groups A [n=14; LAR with soiling] and B [n=15; LAR without soiling], compared to group C [n=29; control subjects, 19 men and 10 women aged 40 to 66 years (mean: age of 56.5 years)]. Methods: 1) Pudendal nerve motor latency was studied by stimulation of nerve roots S2-4 by magnetic stimulation (SMS) to determine the time interval between magnetic stimulation and the first muscle contraction of the external anal sphincter. The pudendal nerve terminal motor latency of the right, left, and posterior side of the anal canal were determined. 2) Anal mucosal electric sensitivity was measured using an anal mucosal electric sensitivity test (AMES); The anal canal length was divided into 3 zones: lower [portion below 1 cmfrom the dentate line (DL)] , middle (DL), and upper zone of the anal canal (portion above 1 cmfrom the DL). A small electric current from a constant current generator was passed between the electrodes until the patient felt a sensation often described as tingling or pulsing. Results: 1) SMS: The conduction delay in group A was significantly longer than in groups B (p<0.01) and C (p<0.01). The conduction delay in group B was significantly longer than that in group C (p<0.01). The conduction delay of SMS in patients with soiling was the longest. 2) AMES: In group C, recording at the middle zone showed the best results. Patients in group A showed the worst results in anal mucosal sensation. Sensation in group A was significantly duller than in group B at the upper (p<0.05) and middle (p<0.05) zones. Conclusion: These findings suggest that involuntary defecation (soiling) after LAR may be due to the damage to both the pudendal motor nerve and sensory nerve.

Key words
soiling, pudendal nerve terminal motor latency by sacral magnetic stimulation, anal mucosal sensory test, anterior resection, rectal cancer

Reprint requests
Seigo Igarashi First Department of Surgery, Nihon University School of Medicine
30-1 Oyaguchi Kamimachi, Itabashi-ku, 173-0032 JAPAN

Accepted
April 27, 2005

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