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Electromyography guides toward subgroups of mutations in muscle channelopathies

Authors

  • Emmanuel Fournier MD, PhD,

    Corresponding author
    1. Department of Physiology, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
    • Département de Physiologie, Faculté de Médecine Pitié-Salpêtrière, 91 Bd de l'Hôpital, 75651 Paris CEDEX 13, France
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  • Marianne Arzel MD,

    1. Department of Physiology, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
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  • Damien Sternberg MD, PhD,

    1. Department of Biochemistry, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
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  • Savine Vicart MD,

    1. Institut National de la Santé et de la Recherche Médicale, UMR546, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
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  • Pascal Laforet MD,

    1. Institute of Myology, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
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  • Bruno Eymard MD, PhD,

    1. Institute of Myology, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
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  • Jean-Claude Willer MD, PhD,

    1. Department of Physiology, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
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  • Nacira Tabti MD, PhD,

    1. Institut National de la Santé et de la Recherche Médicale, UMR546, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
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  • Bertrand Fontaine MD, PhD

    1. Institut National de la Santé et de la Recherche Médicale, UMR546, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
    2. Fédération de Neurologie, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France
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Abstract

Myotonic syndromes and periodic paralyses are rare disorders of skeletal muscle characterized mainly by muscle stiffness or episodic attacks of weakness. Familial forms are caused by mutations in genes coding for skeletal muscle voltage-gated ion channels. Exercise is known to trigger, aggravate, or relieve the symptoms. Therefore, exercise can be used as a functional test in electromyography to improve the diagnosis of these muscle disorders. Abnormal changes in the compound muscle action potential can be disclosed using different exercise tests. We report the outcome of an inclusive electromyographic survey of a large population of patients with identified ion channel gene defects. Standardized protocols comprising short and long exercise tests were applied on 41 unaffected control subjects and on 51 case patients with chloride, sodium, or calcium channel mutations known to cause myotonia or periodic paralysis. These tests disclosed significant changes of compound muscle action potential, which generally matched the clinical symptoms. Combining the responses to the different tests defined five electromyographic patterns (I–V) that correlated with subgroups of mutations and may be used in clinical practice as guides for molecular diagnosis. We hypothesize that mutations are segregated into the different electromyographic patterns according to the underlying pathophysiological mechanisms. Ann Neurol 2004

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