Latency and amplitude variability in serial median nerve SEP recordings

Objectives: Intra-individual variability of SEP parameters was investigated by serial SEP recordings. Methods: Median nerve SEP of 53 normal subjects (mean age 25.5 +/- 2.7 year s) were evaluated. Recordings were repeated 1 week, 2 weeks, and 6 months a fter the initial recording. Results: Mean values of latencies from right median nerve stimulation were slightly longer (+0.1 ms) as compared to the: left. The intraindividual (wi thin stimulation side) variance did not depend on the time interval between recordings. The total within-stimulation-side variance of latencies was 0. 056 ms(2) for N20 (Cu-3/4' vs. F-z), 0.070 ms(2) for N13 (C-7 vs. F-z), 0.0 48 ms(2) for N10 (Erb's point vs. F-z), 0.11 ms(2) for P9 (C-3/4' vs. contr alateral forearm), and 0.148 ms(2) for P14 (C-3/4' VS. contralateral forear m), and was about 3 times smaller than between-side variability with regard to cortical or spinal potentials. Upper limits for latency differences and lower Limits for amplitude ratios in repeated recordings, as well as upper and lower limits for between-side latency differences and amplitude ratios were calculated, using F distributions with worst-case assumptions for deg rees of freedom and error probability P = 0.05. Upper limits of within-stim ulation-side latency differences were 0.55 ms for N20, 0.62 ms for N13, 0.5 1 ms for N10, 0.78 ms for P9, and 0.90 ms for P14, and corresponding lower limits of amplitude ratios were 0.69, 0.62, 0.66, 0.45, and 0.50, respectiv ely. Conclusions: Our results demonstrate a small systematic, and a larger rando m difference between right and left side stimulation, one arising from the peripheral, and the other one from the central pathway proximal to the sour ce of N10. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.