ABSTRACT
Amyotrophic lateral sclerosis (ALS), also called Charcot’s disease or Lou Gehrig’s disease, belongs to a larger group of disorders affecting the motor neurons. A relay of two systems of motor neurons, the upper motor neuron (UMN) and lower motor neuron (LMN), controls voluntary muscles, and symptoms can vary based on the degree of involvement of each component of this relay system. Disorders of the motor neuron can be classified based on the involvement of one or both components of the relay system (Tables 1a and 1b). Other overlapping classifications are based on the topography of involvement (primary lateral sclerosis, spastic paraparesis, spinal muscular atrophy, and progressive bulbar palsy) (Table 2). ALS involves both the UMN and LMN.
