GIANT SOMATOSENSORY EVOKED-POTENTIALS IN A PATIENT WITH THE ANTERIOR SPINAL ARTERY SYNDROME

We studied a previously healthy 25-year-old woman with the anterior sp inal artery syndrome, a rare thoracocervical myelopathy with multiple potential etiologies. Quantitative and clinical sensory examination sh owed dissociated loss of pin-prick and temperature discrimination belo w the level of the lesion, with normal light touch, vibratory, and pos ition sense. Magnetic resonance imaging was consistent with cervical s pinal cord infarction. Median SEPs showed normal Erb's potential with absent spinal N13BAR and normal scalp N20BAR latency. Tibial SEPs show ed normal lumbosacral responses and normal scalp P30BAR latency. Both median and tibial nerve stimulation produced cortical responses of unu sually large amplitude (median 38 muV, tibial 17 muV). We hypothesize that large SEP amplitudes in this patient resulted from loss of antero lateral inhibitory influences on the dorsal column-medial lemniscal sy stem.