Sphincter electromyography and the penilo-cavernosus reflex: are both necessary?

For electrodiagnostic assessment of patients with suspected peripheral sacral nerve lesions, sphincter muscle electromyography (EMG) and sacral reflex testing are mainly used. However, it has not been established whether a single test or both tests are necessary in individual patients. The present study aimed to clarify this dilemma.

Fifty-two men with clinical, electrodiagnostic and radiological signs supportive of chronic cauda equina or conus medullaris lesions were included. Clinical examination, including perianal sensation and penilo-cavernosus reflex testing, and neurophysiologic testing, including quantitative anal sphincter EMG and penilo-cavernosus reflex testing (on single and double electrical, and mechanical stimulation), were performed separately on each side. The more abnormal side on EMG and sacral reflex testing was analyzed.

Quantitative anal sphincter EMG was abnormal in 73%, neurophysiologic testing of the penilo-cavernosus reflex (using different stimulation techniques) in 81-83%, and their combination in 94-96% of patients. The penilo-cavernosus reflex measurement was pathologic in 79-86% of patients with normal quantitative EMG, and quantitative EMG in 81-83% of patients with a normal reflex.

The study supports the clinical utility of an electrodiagnostic protocol for assessment of men with suspected peripheral sacral lesions that includes both quantitative anal sphincter EMG and sacral reflex studies.