Clinical and neurophysiologic testing of the penilo-cavernosus reflex

Both clinical and neurophysiologic testing of the penilo-cavernosus reflex is used in clinical practice. The aim of the present study was to determine the as yet unestablished potential contribution of sacral reflex testing to the diagnostic evaluation of patients with suspected neuropathic sacral lesions.

Fifty-three men with clinical, electrodiagnostic, and radiologic signs of chronic cauda equina or conus medullaris lesions were studied. Clinical examination, including assessment of anal sphincter tone and perianal sensation, and both clinical and neurophysiologic testing of the penilo-cavernosus reflex, were performed. The sacral reflex was elicited on a single (normal latency: <39.4 msec) and double (<36.0 msec) electrical, and on mechanical stimulation (<35.5 msec). Responses were recorded by a concentric needle electrode inserted consecutively into the left and right bulbocavernosus muscles. The response from the more abnormal side was further analyzed.

Clinical testing of the penilo-cavernosus reflex was abnormal in 81% of patients with normal anal squeeze, in 78% with normal perianal sensation, and in 50-67% with bilaterally normal neurophysiologic findings on three different stimulation techniques. Neurophysiologic testing of the reflex was abnormal in 69-94% of patients with normal anal squeeze, in 56-67% with normal perianal sensation, and in 44-67% of patients with a clinically normal reflex.

The study supported the clinical utility of both clinical and neurophysiologic measurement of the penilo-cavernosus reflex.