What is amyotrophic lateral sclerosis (ALS)?

Updated: Jan 02, 2020
  • Author: Divakara Kedlaya, MBBS; Chief Editor: Ryan O Stephenson, DO  more...
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Amyotrophic lateral sclerosis (ALS) is the most common type of adult-onset motor neuron disease (MND). Adult-onset motor neuron diseases are a group of neurologic disorders that present in adult life and are characterized primarily by progressive degeneration and loss of motor neurons. ALS involves upper and lower motor neurons and presents as an idiopathic, progressive degeneration of anterior horn cells and their associated neurons, resulting in progressive muscle weakness, atrophy, and fasciculations. [1, 2, 3]

The disease was first described in 1869 and is commonly called Lou Gehrig disease, after the professional baseball player who died of ALS in 1941.

Other diseases classified as adult-onset motor neuron diseases have more restricted presentations and can evolve into idiopathic ALS if the patient is tracked for a long period. These diseases include the following:

  • Progressive bulbar palsy - Pure bulbar involvement

  • Progressive muscular atrophy - Pure lower motor neuron degeneration

  • Primary lateral sclerosis - Pure upper motor neuron degeneration

  • Adult-onset spinal muscular atrophy - Includes a broad range of primary motor neuron diseases classified by pattern of inheritance, distribution of weakness, or age of onset

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