Fistula in ano surgery has no impact on pudendal nerve terminal motor latency

Anal fistula surgery is recognized as a major risk factor for anal incontinence. This incontinence is mainly due to surgical sphincter lesions, although a neurogenic mechanism through damage to the pudendal nerve is not excluded. The objective of our study was to evaluate the influence of anal surgery on the anal terminal motor latency of the pudendal nerve (PNTML).

The PNTML values were measured pre- and postoperatively, respectively, in 33 patients (28 men, 5 women) treated for anal suppuration and 34 patients (21 men, 13 women) undergoing pedicular hemorrhoidectomy using the Milligan and Morgan technique.

The average age was 49.6 years in the hemorrhoid group and 45 years in the fistula group (p=0.19). There was no difference in the sex ratio between the two groups (p=0.06). In the anal fistula group, the preoperative mean PNTML was 2.42 (+/-0.46) ms on the infected side and 2.40 (+/-0.42) ms on the healthy side, with a significant difference from the control group's preoperative ipsilateral latencies: 2.73 (+/-0.60) ms (p=0.02, p=0.01). The variations in the postoperative PNTML of the fistula group, both on the healthy side (DeltaPNTML=0.06+/-0.42 ms) and on the diseased side (DeltaPNTML=0.03+/-0.40 ms), are comparable with those of the hemorrhoid group (DeltaPNTML=0.01+/-0.48 ms; p=0.63, p=0.84).

The nervous conduction of the pudendal nerves does not seem to be altered by the presence of an infectious process in the ischiorectal fossa nor by the surgical procedure. However, a more refined electrophysiological study would seem to be necessary to assess the repercussions on the perineal innervation.