Purpose: Pudendal nerve complete motor latency, or the sum of the conduction time from the root of the sacral nerve to the end of the pudendal nerve and the synaptic delay, varied in length (from shortest to longest) in the puborectalis, the deep external anal sphincter, and the superficial/subcutaneous external anal sphincter, in that order, for middle-aged people. The aim of this study was to elucidate whether such a phenomenon was physiologic or pathologic.
Methods: In 20 young adults (21.9 +/- 1.37 years old, 10 females), pudendal nerve complete motor latencies were measured after magnetic stimulation to the sacral region. Electromyographic recordings were taken at depths of 5, 3.8, 2.6, and 1.5 cm from the perineal skin using a needle electrode and at 3 cm from the anal verge using surface electrodes within the anal canal. The data were compared with the data of the middle-aged cohort (65.4 +/- 7.70 years old) in our previous study.
Results: The pudendal nerve complete motor latencies were 3.85 +/- 1.24 ms at 5 cm, 3.97 +/- 1.25 ms at 3.8 cm, 5.41 +/- 2.42 ms at 2.6 cm, 9.98 +/- 4.01 ms at 1.5 cm, and 3.45 +/- 0.52 ms while using surface electrodes. The pudendal nerve complete motor latencies at 5, 3.8, and 2.6 cm were significantly shorter in the young adults than in the middle-aged subjects. The pudendal nerve complete motor latency using surface electrodes was significantly shorter than the pudendal nerve complete motor latency at 2.6 and 1.5 cm (mean +/- standard deviation).
Conclusions: Because pudendal nerve complete motor latency was progressively longer at 5, 3.8, 2.6, and 1.5 cm, in that order, in young adults as well as in middle-aged people, this phenomenon was considered to be physiologic and may be mechanically reasonable and safe in shutting the anal canal and might be useful for milking the residual mucus out of the anal canal to prevent soiling. Aging disturbed the innervation of the upper three levels of the anal sphincter system. Pudendal nerve complete motor latency using intra-anal surface electrodes approximated that at the highest of the anal sphincters.