Clinical diagnosis of propriospinal myoclonus is unreliable: An electrophysiologic study

Authors

  • Roberto Erro MD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, University College London (UCL) Institute of Neurology, London, United Kingdom
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  • Kailash P. Bhatia MD, FRCP,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, University College London (UCL) Institute of Neurology, London, United Kingdom
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  • Mark J. Edwards PhD, MRCP,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, University College London (UCL) Institute of Neurology, London, United Kingdom
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  • Simon F. Farmer FRCP, PhD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, University College London (UCL) Institute of Neurology, London, United Kingdom
    2. Department of Neurology, National Hospital for Neurology and Neurosurgery, London, United Kingdom
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  • Carla Cordivari MD

    Corresponding author
    1. Department of Clinical Neurophysiology, National Hospital for Neurology and Neurosurgery, London, United Kingdom
    • Correspondence to: Dr. Carla Cordivari, Consultant in Neurophysiology, National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK; carla.cordivari@uclh.nhs.uk

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  • Relevant conflicts of interest/financial disclosures: Nothing to report.

  • Full financial disclosures and author roles may be found in the online version of this article.

ABSTRACT

Propriospinal myoclonus is a rare movement disorder that is hypothesized to arise from a spinal generator that transmits activity up and down the spinal cord via long propriospinal pathways. Polymyography is mandatory for the diagnosis, but the typical electrophysiological pattern described for propriospinal myoclonus has been also found in patients with psychogenic axial jerks, supported by the presence of a Bereitschaftspotential (BP; from German, “readiness potential,” also called the premotor potential). We evaluated polymyographic findings in 65 patients referred to us with a clinical diagnosis of propriospinal myoclonus and also looked for the presence of the BP, as detected by jerk-locked back-averaging. At clinical reassessment by a movement disorder specialist, nearly one-half of the patients had clinical clues suggestive of a psychogenic cause of the jerks. Electrophysiological studies were carried out on all 65 patients. Polymyography findings revealed an incongruent electromyographic pattern for propriospinal myoclonus in 84.6% of patients and the presence of the BP in 86.1% of the entire cohort. When taking into account either the presence of BP and/or incongruence of polymyographic features, all patients, including the approximately 50% clinically diagnosed as organic propriospinal myoclonus by a movement disorder expert, had strong neurophysiological evidence for a psychogenic origin of their jerks. The clinical distinction of propriospinal myoclonus from psychogenic axial jerks is unreliable. This is the largest cohort of patients with axial jerks reported so far and we suggest that most of the patients with a clinical picture that clinically resembles propriospinal myoclonus are likely to be psychogenic. © 2013 International Parkinson and Movement Disorder Society

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