Somatosensory evoked potentials in spinal cord diseases

Somatosensory evoked potentials (SEPs) were studied in 115 patients with spinal cord diseases (multiple sclerosis, amyotrophic lateral sclerosis, cervical myelopathy, subacute combined degeneration, myelitis, spinal cord injury, tumours). The SEPs were recorded at three levels: parietal, spinal (cervical or lumbar), and at the Erb point. The central conduction time was also estimated (N9-N13 and lumbar potential (LP): LP-P37). The most sensitive test (95% abnormalities) was represented by the cortical recording of the SEPs when the tibial nerve was stimulated. The interval LP-P37 was increased, the SEPs being delayed or unrecordable and desynchronized (in cases of polyneuropathies only the latency was increased whereas the waveform was normal). In 50 patients with definite form of multiple sclerosis (MS) abnormalities of the cervical potential N13 were obtained in 96% of cases. The cortical SEPs to the median nerve stimulation were abnormal in 64% of cases only (32 patients). Of 10 patients with amyotrophic lateral sclerosis (ALS), cortical SEPs to the lower limb stimulation were abnormal in 6 patients (20%) and only 2 patients had also abnormal N13 and N20. Of 15 patients with cervical myelopathy, SEPs to the tibial nerve stimulation were abnormal and N9-N13 delayed in all but 2 patients. All the 5 patients with subacute combined degeneration had abnormal SEPs to the tibial nerve stimulation. In all the 15 patients with inflammatory spinal cord diseases, the SEPs were abnormal and the central conduction time was delayed. In 5 cases with spinal cord injury the SEPs were absent above the lesion. In 15 patients with tumoral compression SEPs to the stimulation of the nerve dependent on the sensitive root compressed as well as the lower limb SEPs were abnormal.