Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society
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J Clin Neurophysiol · Jul 1996
Case ReportsRecovery from brain-stem lesions involving the nociceptive pathways: comparison of clinical findings with laser-evoked potentials.
Dissociated sensory impairment in brain-stem disorders suggests a lateral lesion involving the spinothalamic tract. Evoked potential studies of the somatosensory system with standard electrical stimulation (SEP) generally fail to establish objective correlates of such sensory deficits, because electrical stimuli predominantly activate large myelinated fibers that project into the medial lemniscal system. In contrast, laser-evoked potentials (LEPs), in response to brief radiant heat pulses, stimulate nociceptive afferents of the superficial skin and allow evaluation of thin fiber and spinothalamic tract function. ⋯ The peak-to-peak amplitude of the main LEP component (N250-P400) correlated significantly with clinical pain sensitivity scored by standardized sensory testing (r = 0.76, p < 0.01). In contrast, early and late SEPs, after standard electrical median or tibial nerve stimulation, were normal in all patients, consistent with their intact mechanosensitivity. In conclusion, LEP studies allow the status of nociceptive function to be objectively and reliably documented on repeated examinations and therefore provide a useful supplement to multimodal sensory assessment in brain-stem disorders.