Cold extends electromyography distinction between ion channel mutations causing myotonia
2006; Wiley; Volume: 60; Issue: 3 Linguagem: Inglês
10.1002/ana.20905
ISSN1531-8249
AutoresEmmanuel Fournier, Karine Viala, Hélène Gervais, Damien Sternberg, Marianne Arzel-Hézode, Pascal Laforêt, B. Eymard, Nacira Tabti, Jean‐Claude Willer, Christophe Vial, Bertrand Fontaine,
Tópico(s)Genetic Neurodegenerative Diseases
ResumoAbstract Objective Myotonias are inherited disorders of the skeletal muscle excitability. Nondystrophic forms are caused by mutations in genes coding for the muscle chloride or sodium channel. Myotonia is either relieved or worsened by repeated exercise and can merge into flaccid weakness during exposure to cold, according to causal mutations. We designed an easy electromyography (EMG) protocol combining repeated short exercise and cold as provocative tests to discriminate groups of mutations. Methods Surface‐recorded compound muscle action potential was used to monitor muscle electrical activity. The protocol was applied on 31 unaffected control subjects and on a large population of 54 patients with chloride or sodium channel mutations known to cause the different forms of myotonia. Results In patients, repeated short exercise test at room temperature disclosed three distinct abnormal patterns of compound muscle action potential changes (I‐III), which matched the clinical symptoms. Combining repeated exercise with cold exposure clarified the EMG patterns in a way that enabled a clear correlation between the electrophysiological and genetic defects. Interpretation We hypothesize that segregation of mutations into the different EMG patterns depended on the underlying pathophysiological mechanisms. Results allow us to suggest EMG guidelines for the molecular diagnosis, which can be used in clinical practice. Ann Neurol 2006
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