Electrophysiological study of the bulbocavernosus reflex: normative data

Abstract

In the clinical setting the bulbocavernosus reflex (BCR) is elicited by squeezing the glans penis and digitally palpating the contraction of the bulbocavernosus (BC) muscle. In neurophysiology the BCR is obtained by stimulating the dorsal nerve of the penis or clitoris and by recording the response from BC muscle and it should be performed in selected patients with suspected urinary, bowel, or sexual neurogenic dysfunction. The BCR is considered one of the sacral neurophysiological tests of the greatest clinical utility. Previous normative data were obtained on small samples. The aim of this study was to determine normative values for the BCR in a large sample of men. We studied a large population (105 men; mean age 53 years, range 19-73 years) without central or peripheral neurological diseases. In each subject the sacral reflex was elicited by electrical stimulation of the base of the dorsum penis and recorded using a surface electrode from the BC muscle. We recorded the latency, calculated at onset, and the maximal amplitude of response, calculated peak to peak. We were able to detect the BCR in all the men. No correlation between BCR latency and age was found (r=0.136; p=0.160). The mean onset latency value was 33.0±4.85 ms (mean±2SD, range 26.8-39.4). The mean amplitude value was 16.53±12.21 μV (mean±2SD, range 4.2-43.6). Our normative data on the BCR were similar to previously published data.

Figure 1

Schematization of the afferent and efferent arcs of the bulbocavernosus reflex.

Figure 2

Example of the bulbocavernosus reflex. Two traces obtained from the same subject. Note the reproducibility of the response.