Median nerve motor conduction to the abductor pollicis brevis.

The median motor conduction study to the abductor pollicis brevis is one of the most commonly performed electrodiagnostic studies, yet there is a need for a more comprehensive normative database for this test. Demographic subgroups of age, gender, and height need to be evaluated with a large enough sample size using modern statistical and electrodiagnostic techniques. In this study, 249 subjects were tested and the following were recorded: latency, amplitude, area, duration, and nerve conduction velocity (NCV). A repeated measures analysis of variance was performed with the waveform measures as the dependent variables and age, gender, and height as the independent variables. Factors that were significant at the P < or = 0.01 level were used to create separate normative databases. Gender was found to be associated with different results for latency and NCV. Age was found to be associated with different results for latency, amplitude, area, and NCV. Once these statistically significant factors were determined, Tukey adjusted pair-wise comparisons of least squares means were used to collapse categories (by decade for age) that were not significantly different from each other at the P < or = 0.05 level. Categories for measures that differed by clinically insignificant amounts (defined as 0.2 ms or less for time measures, 2 m/s or less for NCV, or 5% or less for amplitude and area) were combined as well. Side-to-side and proximal-to-distal differences were analyzed. The normal range was derived as mean +/- 2 standard deviations and at the 97th (third) percentiles of observed values. The findings are presented in this article but include a mean latency of 3.7 +/- 0.5 ms, a mean amplitude of 10.2 +/- 3.6 mV, and a mean nerve conduction velocity of 57 +/- 5 m/s. Subgroupings based on demographic characteristics, percentile distributions, side-to-side, and proximal-to-distal variations are presented.