Spinal somatosensory evoked potentials in patients with tethered cord syndrome.

We studied the electrophysiological changes occurring in six patients with tethered cord syndrome. Evidence of spinal malformations was provided by magnetic resonance imaging. The functional assessment of the spinal cord was performed by analysing both spinal and cortical somatosensory evoked potentials. The evoked electrospinogram was recorded from the thoracic and lumbosacral spinous processes. The N22 lumbosacral potential was selectively affected, being rostrocaudally displaced and reduced in amplitude or even absent in patients with neurological signs indicating a segmental lower cord lesion. Inter-peak somatosensory evoked potentials latency was normal in all cases, suggesting that ascending axonal potentials in the dorsal column fibres may be synchronized. Segmental potentials of the lumbosacral response, originating from the post-synaptic activity of dorsal horn interneurons, are selectively affected in this syndrome resulting from the rostrocaudal displacement of the spinal cord due to tethering. Our findings in the clinical field are consistent with previous experimental evidence indicating a different sensitivity of the gray vs. white matter to progressive stretching.