Somatosensory evoked potentials in patients with sensitive dissociation.

The purpose of the study was to reconsider the somatosensory evoked potential (SEP) morphology in case of thermalgic versus proprioceptive sensory loss. The study was carried out on 70 inpatients affected by uni- or bilateral dissociated sensory disorders and on 45 normal controls. The median or tibial nerves were stimulated (at wrist or ankle), the stimulus intensity being adjusted to elicit a visible muscle response with liminal pain. SEPs were measured with regard to 7 negative components parameters (latency, amplitude) and statistically compared in the three groups. Results show that the initial SEP components (N18, N30, N70) are specifically affected in case of proprioceptive and the late components (N150, N220, N340) in case of thermalgic sensory disorders (N150 having an intermediate position). The intergroup differences were statistically significant. The results are thought to be used in clinical diagnosis.