Correlation between distal motor latency and compound muscle action potential in amyotrophic lateral sclerosis.

OBJECTIVES

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder, characterized by a selective progressive degeneration of the motor system. Electromyography is essential for the diagnosis of ALS. The measurement of motor conduction of peripheral nerves is of major importance to recognize other possible causes of progressive muscle wasting. However, there are also pathologic changes in nerve conduction studies in ALS patients.

METHODS

In this study we analysed the values of distal motor latency (DML), compound muscle action potential (CMAP) and motor nerve conduction velocity (MNCV) in 95 patients with definite ALS.

RESULTS

We found slight slowing of MNCV and moderate to strong reduction of CMAP and a prolongation of DML. We found no significant correlation between MNCV and CMAP.

DISCUSSION

The main finding of the present work was the negative correlation between DML and CMAP. It is interpreted as a very distal axonal damage as the main reason for prolongation of DML in ALS patients.