TEMPERATURE CORRECTION FACTORS DERIVED FROM NORMAL SUBJECTS MAY BE INVALID IN DEMYELINATING NEUROPATHIES

This study investigates the temperature effect on motor nerve conducti on velocity (MNCV) in patients with neuropathic processes. Fourteen su bjects, ages 18-77 yr old, with a diagnosis of uremic polyneuropathies (UPN, n = 5), diabetic polyneuropathies (DPN, n = 6) or carpal tunnel syndrome (CTS, n = 3) and ten normal controls were studied. After lim b cooling in a cold water bath for 30 min, skin temperatures were sequ entially obtained from the volar midwrist. Motor conduction velocities were obtained at 2-3 degrees increments between 22 and 33 degrees C. Results indicated a large individual variability; 0.1 to 1.8 in the me dian and 0.8 to 2.0 m/s/degrees C in the ulnar nerve when all three gr oups are considered together. There was a significant difference betwe en the correction factors for control v DPN and control v CTS. A signi ficant difference was also present for UPN v DPN and UPN v CTS (p < 0. 05). There was a positive correlation (r = 0.746, p = 0.0001) between the baseline conduction velocities and the size of the correction fact ors in all the subjects. The effect of temperature on MNCV appears to be inversely correlated with the severity of conduction slowing or dem yelination. These findings suggest that the use of a correction factor may be invalid when studying a demyelinated nerve, and that the extre mity should be warmed to a specific temperature before an electrodiagn ostic study.