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

AIMS: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.