Sacral neurophysiologic study in patients with chronic spinal cord injury

Neurophysiologic testing of the sacral reflex has demonstrated utility in the diagnosis of sacral lower motor neuron lesions. The aim of the present study was to also apply this test to patients with upper motor neuron lesions.

A group of 16 male patients with chronic suprasacral spinal cord lesions was prospectively recruited. In addition to history and clinical neurologic examination (including anal sphincter tone, saddle sensation, and penilo-cavernosus reflex testing), sacral neurophysiologic studies were performed. Neurophysiologic testing included quantitative electromyography of the external anal sphincter (motor unit potential (MUP) count during relaxation and MUP analysis), and neurophysiologic measurement of the penilo-cavernosus reflex (elicitation threshold and latency) on electrical stimulation. The findings were compared to data obtained in the control group of 26 men.

Clinical elicitability of the penilo-cavernosus reflex was increased, and the neurophysiologically measured reflex threshold reduced in patients (<0.02). No significant differences were found in clinical assessment of anal sphincter tone, MUP count, reflex latency, and quantitative MUP analysis. The diagnostic sensitivity of individual parameters was low (≤25%).

In patients with chronic spinal cord injury, increased elicitability of the penilo-cavernosus reflex was found. However, none of the assessed neurophysiologic parameters was found to assist in the diagnosis of the sacral upper motor neuron lesion in individual patients. The shortened sacral reflex latency found in individual patients is therefore not a consequence of a suprasegmental lesion, but rather of the low position of the conus medullaris (e.g., in tethered cord syndrome).