Neurophysiology in amyotrophic lateral sclerosis and other motor degenerations

Electromyography is critical for the diagnosis of motor neuron disease, as its findings exclude mimicking disorders, and confirm signs of widespread motor unit loss and reinnervation. In chronic conditions the slow disease course allows giant, stable motor unit potentials to appear. In contrast, in amyotrophic lateral sclerosis, the rapid degenerative process is characterized by signs of denervation and unstable motor unit potentials, where motor units become dysfunctional before having time to sustain very large reinnervated motor unit potentials. Fasciculation potentials are observed in both conditions. In amyotrophic lateral sclerosis fasciculation potentials are important supporting electrodiagnostic evidence, permitting earlier diagnosis. Many methods have been developed to quantify and monitor the lower motor neuron pool, but few have been used in clinical trials. Their role as tools to follow interventions or to interpret pathogenesis remains incompletely explored. Electromyography is a sensitive and reliable test in the diagnosis and assessment of motor neuron diseases.