Evaluation of the motor and sensory components of the pudendal nerve

Extensive neurophysiological investigations consisting of different techniques to evaluate the efferents and afferents of the pudendal nerve were carried out in 27 healthy subjects. These investigations included motor evoked potential recordings from the external anal sphincter in response to magnetic stimulation of the cortex and lumbosacral roots, measurement of sacral reflex latency to magnetic and electrical stimulation, and cortical sensory evoked potential recording after stimulation of the dorso-genital nerve and anal canal. Motor latencies after transcranial magnetic stimulation to the anal sphincter were 25.1 +/- 2.9 msec at rest and 20.9 +/- 2.0 msec with voluntary sphincter contraction (facilitation). Motor latency after lumbosacral root stimulation was 3.7 +/- 1.0 msec. Mean sacral reflex latency after magnetic stimulation was 43.8 +/- 11.2 msec and was significantly longer than after electrical stimulation (37.0 +/- 7.2 msec; P < 0.05). P1 latency of the sensory evoked potentials after dorso-genital nerve stimulation was 40 +/- 3 msec and was significantly shorter than after anal stimulation 46 +/- 3 msec (P < 0.01). Evoked potential recording allows us to study both upper and lower motor neuron components to the anal sphincter. The present study paves the way for the combined application of these tests in the evaluation of disorders of the pelvic floor.