Maximal and minimal motor conduction velocity in amyotrophic lateral sclerosis and X-linked bulbospinal muscular atrophy measured by Harayama's collision method.

Measurement of the maximal (Vmax) and minimal (Vmin) motor nerve conduction velocities was performed in amyotrophic lateral sclerosis (ALS), bulbospinal muscular atrophy (BSMA), and control subjects. The collision method as described initially by Harayama and coworkers was used. This allowed for the correction of the velocity recovery effect (VRE) in Hopf's original method. The purpose of this study is to clarify the controversial results regarding the Vmin and the difference between Vmax and Vmin (Vmax-Vmin) in ALS and to compare these results with BSMA, and clarify the usefulness of Harayama's method. In ALS, a reduction of Vmax and Vmin, and an increase of Vmax-Vmin were found in both median and posterior tibial nerve. In BSMA, a reduction of Vmin and an increase of Vmax-Vmin in the median nerve were noted. Some patients whose results of conventional nerve conduction study were entirely within normal range showed abnormal results in Vmin and/or Vmax-Vmin. These results suggest that the correction of VRE is essential to determine a Vmin, and motor fibers with abnormally slow conduction velocities were present in ALS and BSMA. Harayama's collision method is useful to detect abnormalities of motor fibers with submaximal conduction velocities.