F tacheodispersion: quantitative analysis of motor fiber conduction velocities in patients with polyneuropathy.

The distribution of motor fiber conduction velocities (FCVs) of the ulnar and peroneal nerves in patients with polyneuropathy was estimated using F tacheodispersion, a technique based on F wave latencies. Twenty-three ulnar and 23 peroneal nerves were studied. Three groups of nerves were identified according to conventional, M response, and F wave measurements: those with all parameters normal (group 1), those with abnormal F wave parameters only (group 2), and those with all parameters abnormal (group 3). Application of F tacheodispersion to nerves in group 1 revealed a shift of the distribution of FCVs toward the lower normal values in 6 of 7 nerves. In group 2, a significant proportion of FCVs were below the lower normal limits despite normal maximum conduction velocity estimated by the M response. In group 3, all nerve fibers were abnormally slow. The results indicate that application of F tacheodispersion in clinical practice will increase sensitivity of nerve conduction studies and enable quantitative estimation of conduction in a motor nerve fiber population.