Zusammenfassung
Myotone Serien im Elektromyogramm (EMG) gelten als charakteristischer Befund für myotone Erkrankungen. Elektromyographische Spontanaktivität, die mit myotonen Serien verwechselt werden kann, kommt aber auch bei einer Reihe anderer Erkrankungen vor, so bei der Neuromyotonie und dem Schwartz-Jampel-Syndrom, bei Myositiden, Glykogenosen, einzelnen selteneren Myopathien und bei chronisch neurogenen Erkrankungen. Myotone Serien fehlen nie bei den Chloridkanalmyotonien und werden häufig bei Patienten mit einer der myotonen Dystrophien gefunden. Bei Natriumkanalerkrankungen sind sie meistens unprovoziert nachweisbar, gelegentlich aber nur nach lokaler Muskelkühlung, Arbeits- oder Kaliumbelastung. Sie kommen bei periodischen Paralysen, die nicht auf einer Natriumkanalmutation beruhen, nicht vor. Auf dieser Basis werden Hinweise sowohl zur Differenzialdiagnose der myotonen Dystrophien und der Kanalerkrankungen als auch zur Differenzialdiagnose von Serienentladungen im EMG gegeben.
Abstract
Myotonic discharges in concentric needle electromyography are often considered to be diagnostic for myotonic disorders. However, electromyographic spontaneous activity that can be mistaken for myotonic discharges may occur in a variety of other disorders, such as neuromyotonia, Schwartz-Jampel syndrome, myosites, glycogenoses, a few rare myopathies, and in chronic neurogenic disorders. Myotonic discharges are always present in chloride channel myotonias and frequently in patients with one of the myotonic dystrophies. Myotonic discharges are a frequent finding in patients with sodium channelopathy, but in some patients they occur only by provoking their occurrence via local muscle cooling, work, or potassium load. So far, myotonic discharges have never occurred in patients with periodic paralyses not caused by altered sodium channels. Based on this fact we present pointers to differential diagnosis of myotonic dystrophies and muscle channelopathies as well as to differential diagnosis of myotonic discharges and similar EMG findings.
Key words
Electromyography - myotonia - myotonic discharges - spontaneous activity - channelopathy
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