Successful long-term therapy with flecainide in a family with paramyotonia congenita

Introduction

Paramyotonia congenita (PC) is a neuromuscular disorder caused by point mutations of the sodium channel gene SCN4A that leads to gating defects in the sodium channel of the muscle membranes, thus resulting in a persistent sodium influx into the sarcoplasma. Classic PC phenotype is characterised by episodes of cold-induced stiffness, prominently in the facial and upper limb muscles, exacerbated by a sustained muscular activity (paramyotonia) and followed by a variable degree of weakness. Electromyography (EMG) at rest discloses myotonic bursts and reduced Compound Muscle Action Potential (CMAP) amplitudes, while short-term forearm exercise and cooling tests induce further decrease resulting in electrical silence in some patients. Muscle paralysis, after paramyotonic attacks, may last from a few dozen minutes to 24–48 hours, thus reducing considerable quality of life and autonomy in daily activities. Among voltage-gating sodium channel blockers, mexiletine is considered the drug of choice in PC and other sodium channel myopathies.

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