Clinical studies have consistently demonstrated that SEP abnormalities are associated with sensory deficits of joint position, touch, vibration, and stereognosis. However, when we try to use SEP as an objective method of sensory testing, it is difficult to evaluate the degree of SEP waveform abnormalities with conventional methods. The purpose of this study was to determine the usefulness of tibial nerve SEP as an objective method of sensory testing when the interside ratio of sum of squares

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... SEP waveform analysis was used. We obtained the SEP data and the sensory data in 100 stroke patients (age=59.3+10.5, median duration of stroke 124 days), and as normative data, in 35 volunteer subjects (age=29+7.2) for SEP and in 21 volunteer subjects (age=38.9+14.5) for sensation. The SEP traces were obtained by stimulating the tibial nerve at the ankle on the right side and the left side alternately with an electric pulse. The stimulus intensity was adjusted to produce a good muscle twitch in the abductor hallucis. Thousand sweeps were averaged for each recording and each stimulus side. A complete sweep consisted of 2,000 samples, representing 200ms of time. The scalp recordings were obtained with the recording electrode at the C'z scalp location referred to bilateral earlobes. The interside ratios of sum of squares were calculated using the latency samples between P 35 and P 53 evoked by unaffected and affected side stimulation. Based on the mean and SD of the natural logarithm of the interside ratios of sum of squares for normal subjects, the SEP waveforms in stroke patients were divided into four grades according to the amount of decrease in the interside ratio of sum of squares. We compared the SEP waveform grades to kinetic senses, tactile senses and pain sensations. For statistical analysis, we calculated Spearman's rank order correlation coefficients between the SEP waveform grades and the degrees of sensory deficits. As a result, the correlation coefficients were 0.73 for kinetic senses, 0.46 for tactile senses and 0.23 for pain sensations. The sensitivity and the specificity of this SEP waveform analysis for detecting kinetic sensory deficits were 85 percent and 81 percent respectively. In conclusion, the interside ratio of sum of squares was a useful parameter to analyze the tibial nerve SEP waveform and to evaluate kinetic senses. (Jpn J Rehabil Med 2000; 37: 274-281)