Abstract
Somatosensory evoked potentials (SEPs) elicited by electrical stimulation of the median nerve at the wrist were recorded over the contralateral scalp in 66 persons with cerebrovascular disease (44 with cerebral hemorrhage and 22 with cerebral infarction) who had reached stable plateaus in functional recovery. Loci of the lesions were determined by computerized axial tomography and possible associations of the SEP findings with motor or sensory dysfunction were examined.
Extensive lesions in the cerebral cortex, whether due to infarction or to hemorrhage, gave rise to severe sensorimotor dysfunction in the contralateral arm, and SEPs from median nerve stimulation of the affected arm could not be recorded. Bleeding into the thalamus, posterior limb of the internal capsule, or dorsal portion of the pons resulted in many instances of relatively light motor involvement but marked sensory impairment. In none of these cases did the median nerve SEP appear.
Conversely, some patients with small infarcts had not progressed beyond the stage of synergic movements in motor recovery but suffered no more than slight sensory involvement. In these instances the SEP appeared clearly, resembling the contralateral intact SEP.
Patients with clinically severe sensory involvement exhibited no SEPs; in each case the lesion affected a structure of the lemniscal pathway: the dorsal portion of the pons, the thalamus, or the posterior limb of the internal capsule. SEPs remained intact in patients whose symptoms were motor but not sensory, and SEPs are also known to be recordable in persons under general anesthesia. These findings suggest that disappearance of the scalp SEP to contralateral median nerve stimulation results from damage to a sensory conduction pathway. Absence of the SEP thus appears to qualify as objective evidence of sensory damage in the patient with cerebrovascular disease.
