J Neurol Neurosurg Psychiatry doi:10.1136/jnnp-2012-302315
  • Neurodegeneration
  • Review

Why are upper motor neuron signs difficult to elicit in amyotrophic lateral sclerosis?

  1. Michael Swash1,2
  1. 1Royal London Hospital, Barts and the London School of Medicine, Queen Mary University of London, UK
  2. 2Institute of Neuroscience, University of Lisbon, Portugal
  1. Correspondence to Professor Michael Swash, Royal London Hospital, Barts and the London School of Medicine, Queen Mary University of London, London EC2Y 8BL, UK; mswash{at}
  1. Contributors MS is the sole contributor to this review article.

  • Received 17 January 2012
  • Revised 13 March 2012
  • Accepted 14 March 2012
  • Published Online First 11 April 2012


It is often difficult to identify signs of upper motor neuron lesion in the limbs of patients with amyotrophic lateral sclerosis, in whom there is neurogenic muscle wasting of varying severity. The reasons for this are complex and not related simply to the degree of lower motor neuron muscle wasting but, rather, depend on the pathophysiological abnormalities that develop in response to damage to descending motor pathways and to motor neurons and interneurons in the ventral horns of the spinal cord. The different mechanisms underlying the clinical phenomenology of the functional motor defect in amyotrophic lateral sclerosis, that lead to difficulty in detecting classical upper motor neuron signs, are discussed.


  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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