[Tibial nerve somatosensory evoked potentials localize the responsible level in tandem spinal stenosis: a case report].

An 84-year-old man had experienced unsteadiness while walking and coldness in both lower limbs for about 18 months, with gradual progression. Neurological examination revealed decreased tendon reflexes in the lower extremities, a positive Romberg sign, and a wide-based gait. MRI demonstrated spinal canal stenosis in the cervical and lumbar regions. Because concomitant peripheral neuropathy was suspected, electrophysiological studies were performed. Nerve conduction studies showed no evidence of peripheral neuropathy. Tibial nerve somatosensory evoked potentials (SEP) revealed prolonged N21-P38 interpeak latency and reduced P38 amplitude, suggesting a predominant central conduction disturbance. Based on these findings, thoracic MRI was performed and revealed the most severe spinal cord compression at the T9/10 level. Discectomy and posterior decompression at this level resulted in improvement of gait. Tibial nerve SEP can be useful for identifying the responsible level in tandem spinal stenosis.