Magnetic pudendal neurostimulation: a novel method for measuring pudendal nerve terminal motor latency

Magnetic stimulation (MS) activates the neuromuscular tissue. This effect was used to develop a novel technique for measuring the pudendal nerve terminal motor latency (PNTML) to the external anal sphincter (EAS) in healthy volunteers and patients with fecal incontinence.

The PNTML was studied in 42 healthy volunteers (mean age 44.3 years; 30 men, 12 women) and 18 patients with neurogenic fecal incontinence (mean age 42.8 years; 12 men, 6 women) using two techniques in each subject: the conventional intrarectal glove-mounted and MS. In the MS technique, the pudendal nerve was stimulated by a magnetic stimulator and a magnetic coil fixed to the perianal skin at the base of the ischiorectal fossa. Stimulation parameters were set at 70% of maximum intensity, i.e. 175 J/pulse and 40 Hz frequency. The response of EAS to MS was recorded by a surface electrode applied to the perianal skin in the vicinity of the anal orifice.

In healthy subjects, the PNTML recorded by MS from the right side (mean 2.2 ms) showed no significant difference from the left PNTML (mean 2.1 ms) and both values did not differ significantly from those recorded by the intrarectal method (right 2.2 ms; left 2.1 ms). In incontinent patients, both the right and left PNTML measured by MS exhibited a significant increase compared to the normal (P<0.05, P<0.05, respectively) but no significant difference if compared to values recorded by the intrarectal route.

The results of measuring the PNTML to the EAS by MS were as accurate as those measured by the intrarectal method. However, the MS method seems to be easier and more convenient to the patient.