Zusammenfassung
Myotonien und familiäre periodische Paralysen sind muskuläre Kanalopathien. Ihnen ist eine Störung der muskulären Erregbarkeit gemeinsam, die durch Mutationen in spannungsgesteuerten Na+-, K+-, Ca2+- und Cl−-Kanälen bedingt ist. Üblicherweise verursacht Membranübererregbarkeit myotone Steifigkeit; durch Depolarisation kann die Über- in Untererregbarkeit umschlagen und dadurch eine transiente Muskelschwäche hervorrufen, wie sie bei Patienten mit ausgeprägter Myotonie zu beobachten ist. Eine länger anhaltende Membrandepolarisation ist für alle periodischen Paralysen die gemeinsame Basis der Muskelschwäche. Die Kanalstörung kann interiktal so gut kompensiert sein, dass spezifische exogene oder endogene Trigger zur Auslösung von Schwächeepisoden erforderlich sind. Ein besonderer Trigger ist das Serumkalium, welches das Ruhemembranpotenzial und damit die Erregbarkeit steuert. Für die periodischen Paralysen bekannte Mutationen, deren Wirkung nicht durch Normbedingungen kompensiert werden kann, führen zu einer progressiven Myopathie.
Summary
The myotonias and familial periodic paralyses are muscle channelopathies. They have in common an impaired muscle excitation that is caused by mutations in voltage-gated Na+, K+, Ca2+, and Cl− channels. Membrane hyperexcitability usually results in myotonic stiffness; with increasing membrane depolarization hyperexcitability can be transiently turned into hypoexcitability causing transient weakness as in severe myotonia. Hypoexcitability due to long-lasting depolarization that inhibits action potential generation is the common mechanism for the periodic paralyses. Interictally, the ion channel malfunction may be compensated, so that specific exogenous or endogenous provocative factors are required to produce symptoms in the patients. An especially obvious triggering agent is the level of serum potassium, the ion decisive for resting membrane potential and degree of excitability. Periodic paralysis mutations for which the ion channel malfunction is not fully compensated interictally cause progressive myopathy.
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Jurkat-Rott, K., Lerche, H. & Lehmann-Horn, F. Muskuläre Kanalopathien. Nervenarzt 82, 511–521 (2011). https://doi.org/10.1007/s00115-011-3269-8
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DOI: https://doi.org/10.1007/s00115-011-3269-8