Clinical application of sacral reflex latency

We determined the sacral reflex latency in 108 neurologically normal subjects and 110 patients with neurological lesions by applying stimulating current to the glans penis or clitoris and measuring the response with electrodes inserted in the external urethral and anal sphincters. In normal men the mean latencies were 34.6 plus or minus 5.1 (standard deviation) msec. at the external urethral sphincter and 36.0 plus or minus 5.2 msec. at the external anal sphincter. In normal women the mean latencies were 37.4 plus or minus 5.5 msec. at the external urethral sphincter and 38.6 plus or minus 4.0 msec. at the external anal sphincter. The mean reflex latency in patients with upper motor neuron lesions was significantly shorter. To our knowledge this is the first single electrophysiological test to show a difference between such patients and normal subjects. An increased mean latency was found in patients with lower motor neuron impairment. We conclude that measurement of sacral reflex latency can add to the diagnostic information obtained from conventional electromyography and cystometry.