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| Titre : |
Specificity of electromyographic exercise tests for differentiation between the involved ion channels and types of mutations in inherited muscle channelopathies and in myotonic dystrophy type 2 |
| Type de document : |
Article |
| Auteurs : |
Zidar J |
| Congrès : |
Congrès international de myologie 2008 (International Congress of Myology 2008; 26-30 mai 2008; Marseille, France) |
| Année de publication : |
2008 |
| Pages : |
p. 593 |
| Langues : |
Anglais (eng) |
| Résumé : | The role of electromyographic short and long exercise tests in diagnosing inherited muscle channelopaties is well established. It has been reported that such tests can point to the affected genes or specific mutations. Our aim was to re-examine this hypothesis and, in addition, to test patients with myotonic dystrophy type 2 (DM2). We examined 24 patients: 11 with potassium aggravated myotonia (PAM) (SCN4A: 9 Val445Leu mutation, 2 Ala699Thr), 6 with myotonia congenita (MC) (different CLCN1 mutations), two with hypokalaemic periodic paralysis (HypoK-PP) (CACNA1S and KCNJ2 mutations), and 5 with DM2, where aberrantly spliced RNA produces altered chloride channel protein. Results of the long and short exercise tests were normal or near to normal in 9 PAM (all Val445Leu) patients. A decrease of the compound muscle action potential (CMAP) late after completion of the long exercise and also after short exercise was noted in one of the two Ala699Thr patients but was normal in the other. Five of the 6 MC patients had autosomal dominant and one recessive form of the disease. In none of them, the results of tests differed significantly from normality. The HypoK-PP1 patient, tested when taking acetazolamide, had no abnormalities. In patient with Andersen-Tawil’s syndrome, a progressive decline in CMAP amplitudes after long exercise was noted. In DM2 patients, we found minor deviations from normality with no specific pattern. Number of the examined patients is rather small, especially in the subgroups. The results were largely normal in PAM Val445Leu patients while one Ala699Thr patient a decline of muscle response after long exercise was noted. All MC patients, those with dominantly and recessively inherited disease forms, were normal on these tests. The Hypo-PP patient’s CMAPs declined on long exercise. Specificity of the electromyographic exercise tests seems to be limited, but they may help in decisions for genetic analyses. |
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