Cold extends electromyography distinction between ion channel mutations causing myotonia
E Fournier, K Viala, H Gervais… - Annals of Neurology …, 2006 - Wiley Online Library
E Fournier, K Viala, H Gervais, D Sternberg, M Arzel‐Hézode, P Laforêt, B Eymard, N Tabti…
Annals of Neurology: Official Journal of the American Neurological …, 2006•Wiley Online LibraryObjective 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 …
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 …
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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