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This is a form of motor neurone disease (MND). It is the most common form of MND and accounts for 65% to 85% of all cases of MND (1).

Amyotrophic lateral sclerosis results from lesions to the corticospinal tract and the anterior horn cells and produces the characteristic feature of tonic atrophy - brisk reflexes and fasciculations.

  • a late onset, rapidly progressive and ultimately fatal neurological disorder, caused by the loss of motor neurons in the brain and spinal cord (2)
    • familial aggregation of ALS, with an age-dependent but high penetrance, is a major risk factor for ALS
    • familial ALS (FALS) is clinically and genetically heterogeneous
      • three genes and linkage to four additional gene loci have been identified so far and may either predominantly lead to ALS (ALSI-ALS6) or cause multisystem neurodegeneration with ALS as an occasional symptom (tauopathies, ALS-dementia complex)

This form of the disease includes Progressive Bulbar Palsy (1).

Corticospinal tract degeneration in the absence of significant muscle wasting may be referred to as primary lateral sclerosis (PLS).

  • PLS entity is not universally accepted. Debate continues over whether the disease constitutes a distinct clinical and pathological entity or whether it is a part of the spectrum of MNDs that presents an upper motor neuron (UMN) predominant form of MND (3)
    • prospective analysis of a series of PLS case reports was in agreement with data from other studies suggesting that pure PLS cases have a prolonged course of disease with a high level of independence when compared to other MND (3)


Last reviewed 01/2018