Lower motor neuron involvement examined by quantitative electromyography in amyotrophic lateral sclerosis

The diagnosis of amyotrophic lateral sclerosis (ALS) includes demonstration of lower motor neuron (LMN) and upper motor neuron (UMN) involvement of bulbar and spinal muscles. Electromyography (EMG) is essential to confirm LMN affection in weak muscles, and to demonstrate changes in clinically non-involved muscles. The aim of the study was to determine the relative importance of ongoing (active) denervation, fasciculations, chronic partial denervation with reinnervation at weak effort and loss of motor units at maximal voluntary contraction (MVC) in ALS.