Correlation between somatosensory evoked potentials and sensory disturbance in stroke patients

Somatosensory evoked potentials (SEP) were recorded in 125 (n = 151) stroke patients more than 3 weeks after disease onset and in 55 healthy adults. The correlation between sensory disturbance, N20 amplitude ratio, and the central conduction time (CCT) was then investigated. N20 amplitude ratio was given by the amplitude of the affected side divided by that of the unaffected side and presented as a percentage, while CCT represents the time interval between N20 and N13. For the healthy subjects, normal values of CCT were 6.1 +/- 0.4 msec (20-59 years old) and 6.4 +/- 0.4 msec (over 60 years old). Normal amplitude ratios were left side/right side = 97.5 +/- 16.4% and right side/left side = 105.4 +/- 17.7% with the value at the second standard deviation, 64.7%, representing the normal range of the amplitude ratio. Of 98 stroke patients with an abnormal amplitude ratio and 23 with an abnormal CCT, 91.8% and 95.7%, respectively, had sensory disturbance. Conversely, 82.6% of those with sensory disturbance showed an abnormal amplitude ratio, while only 38.6% with sensory disturbance showed an abnormal CCT. There was a definite correlation between sensory disturbance and either CCT or amplitude ratio, however, there was none between CCT and amplitude ratio. On the basis of these results, we concluded that amplitude ratio would be more effective than CCT as a parameter for monitoring sensory disturbance in stroke patients.