Dermatomal somatosensory evoked potentials of the lumbar and cervical roots. Method and normal values.

We describe a method for obtaining cortical evoked potentials after stimulation of the lumbosacral and cervical dermatomes in healthy volunteers. Such dermatomal evoked potentials are expected to contribute to the diagnosis of lumbar and cervical root entrapment. Normative data are presented for each dermatome including left-right differences. A significant correlation was found between absolute latencies and body length for the lumbosacral segments. This correlation was virtually absent in the cervical segments. The latency difference between the same cervical or lumbosacral dermatome left and right was also independent of body length for all segments.