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Cold extends electromyography distinction between ion channel mutations causing myotonia
Author(s) -
Fournier Emmanuel,
Viala Karine,
Gervais Hélène,
Sternberg Damien,
ArzelHézode Marianne,
Laforêt Pascal,
Eymard Bruno,
Tabti Nacira,
Willer JeanClaude,
Vial Christophe,
Fontaine Bertrand
Publication year - 2006
Publication title -
annals of neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.764
H-Index - 296
eISSN - 1531-8249
pISSN - 0364-5134
DOI - 10.1002/ana.20905
Subject(s) - myotonia , myotonia congenita , electromyography , medicine , skeletal muscle , population , electrophysiology , sodium channel , weakness , physical medicine and rehabilitation , chemistry , myotonic dystrophy , anatomy , sodium , environmental health , organic chemistry
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