Objectives: To determine whether the increase in conduction velocity with temperature (deltav/deltaT) is decreased in axonal polyneuropathy and to compare methods to account for low limb temperature in electroneurography.
Methods: Median nerve motor and sensory conduction and tibial nerve motor conduction were measured in 19 patients with chronic idiopathic axonal polyneuropathy at baseline temperature, after warming at 37 degrees C, and after cooling at 25 degrees C. Deltav/deltaT was determined, using the skin temperature difference and the presumed nerve temperature difference of 12 degrees C. The baseline conduction velocity was corrected for 37 degrees C, using mean deltav/deltaT values for normal subjects taken from the literature.
Results: Deltav/deltaT was positively correlated with the conduction velocity after warming at 37 degrees C: the lower the conduction velocity, the lower the deltav/deltaT. In nerves with a slow conduction velocity, deltav/deltaT was often zero. As slower conducting nerve fibers have smaller deltav/deltaT values, the decreased deltav/deltaT values in our study are probably related to loss of fast conducting fibers. The corrected conduction velocity was usually faster and considerably less often abnormal than the conduction velocity after warming at 37 degrees C. The latter can be considered the gold standard.
Conclusion: Deltav/deltaT may be reduced in axonal polyneuropathy. The correction method is, therefore, not suitable to account for low limb temperature, as the conduction velocity is overestimated.