Median nerve somatosensory evoked potentials and their high-frequency oscillations in amyotrophic lateral sclerosis

Objective To investigate sensory cortical changes in amyotrophic lateral sclerosis (ALS), we studied somatosensory evoked potentials (SEPs) and their high-frequency oscillation potentials. Methods Subjects were 15 healthy volunteers and 26 ALS patients. Median nerve SEPs were recorded and several peaks of oscillations were obtained by digitally filtering raw SEPs. The patients were sorted into three groups according to the level of weakness of abductor pollicis brevis muscle (APB): mild, moderate and severe. The latencies and amplitudes of main and oscillation components of SEP were compared among normal subjects and the three patient groups. Results The early cortical response was enlarged in the moderate weakness group, while it was attenuated in the severe weakness group. No differences were noted in the size ratios of oscillations to the main SEP component between the patients and normal subjects. The central sensory conduction time (CCT) and N20 duration were prolonged in spite of normal other latencies. Conclusions The median nerve SEP amplitude changes are associated with motor disturbances in ALS. The cortical potential enhancement of SEPs with moderate weakness in ALS may reflect some compensatory function of the sensory cortex for motor disturbances. Significance The sensory cortical compensation for motor disturbances is shown in ALS, which must be important information for rehabilitation.