[Dermatomal somatosensory evoked potentials in the diagnosis of focal lesions of the spinal cord].

We studied 13 patients suffering from localized spinal cord lesions by means of somatosensory evoked potentials obtained by electrical stimulation at various dermatome levels (SEPD). The results were compared to those of somatosensory evoked potentials obtained by stimulation of the posterior tibial nerve (SEPpt), as well as to clinical and radiologic data. Structural lesions could be demonstrated in 8 patients; in 5 patients, however, X-rays were normal and/or incompatible with symptoms. We found clear correlations among clinical or radiologic data and the level of lesion indicated by SEPD in all 13 patients. In one case SEPD were abnormal 6 months in advance of the first alteration in magnetic resonance imaging. Abnormal SEPD and SEPpt results were consistent, suggesting the existence of a common central pathway to carry stimuli. SEPD should be considered a useful, reliable technique for assessing spinal cord function, especially when no structural lesion can be demonstrated or when spinal injury is doubtful or when several segments are involved.