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Fasciculation in amyotrophic lateral sclerosis: origin and pathophysiological relevance
  1. Mamede de Carvalho1,2,
  2. Matthew C Kiernan3,
  3. Michael Swash2,4
  1. 1 Department of Neurosciences and Mental Health, Hospital de Santa Maria-CHLN, Lisbon, Portugal
  2. 2 Institute of Physiology-IMM, Faculty of Medicine, University of Lisbon, Lisbon, Portugal
  3. 3 Bushell Chair of Neurology, Sydney Medical School, University of Sydney, Brain & Mind Centre, University of Sydney, Sydney, NSW, Australia
  4. 4 Department of Neurology, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK
  1. Correspondence to Professor Mamede de Carvalho, Institute of Physiology-IMM, Faculty of Medicine, University of Lisbon, Portugal, 1649-028, Lisbon, Portugal; mamedemg{at}


This review considers the origin and significance of fasciculations in neurological practice, with an emphasis on fasciculations in amyotrophic lateral sclerosis (ALS), and in benign fasciculation syndromes. Fasciculation represents a brief spontaneous contraction that affects a small number of muscle fibres, causing a flicker of movement under the skin. While an understanding of the role of fasciculation in ALS remains incomplete, fasciculations derive from ectopic activity generated in the motor system. A proximal origin seems likely to contribute to the generation of fasciculation in the early stages of ALS, while distal sites of origin become more prominent later in the disease, associated with distal motor axonal sprouting as part of the reinnervation response that develops secondary to loss of motor neurons. Fasciculations are distinct from the recurrent trains of axonal firing described in neuromyotonia. Fasciculation without weakness, muscle atrophy or increased tendon reflexes suggests a benign fasciculation syndrome, even when of sudden onset. Regardless of origin, fasciculations often present as the initial abnormality in ALS, an early harbinger of dysfunction and aberrant firing of motor neurons.

  • amyotrophic lateral sclerosis
  • benign fasciculations
  • fasciculations
  • hyperexcitability
  • motor neuron disease

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  • Competing interests None declared.

  • Provenance and peer review Commissioned; externally peer reviewed.