The penilo-cavernosus reflex: comparison of different stimulation techniques

Although several stimulation techniques are available to elicit sacral reflexes, no comparative data on their utility has been published. The aim of the present study was to determine the most sensitive stimulation technique used for neurophysiologic recording of the penilo-cavernosus reflex.

Neurophysiologic measurement of the penilo-cavernosus reflex on single and double pulse electrical, and on mechanical stimulation was performed in 52 men with chronic cauda equina or conus medullaris lesions. Responses were recorded by a standard concentric EMG needle electrode inserted consecutively into the left and right bulbocavernosus muscle. Responses were regarded as abnormal when non-elicitable, of increased latency, or of increased latency compared to the contralateral side, using my previously published normative ranges. Sensitivity was calculated separately for each side using all three stimulation techniques.

Sensitivities of the electrophysiological measurement of the penilo-cavernosus reflex on single electrical, double electrical, and mechanical stimulation were 70%, 73%, and 73%, respectively. The combined use of all three stimulation modalities increased the sensitivity to 82%. The use of interside latency differences did not increase the sensitivity using any of the stimulation modalities.

No significant differences in sensitivity were found between the three stimulation techniques, and only a very modest increase was found on concomitant application of all three. Because of the high elicitability of responses, the lower stimulation strength required, and the opportunity to measure sensory and reflex thresholds, the authors' preference is to use double pulse electrical stimulation.