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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.1 However, mexiletine efficacy has been investigated only in a few heterogeneous small PC series during a month-lasting follow-up.
In experimental studies, flecainide, a class IC antiarrhythmic drug, appeared to be more effective than mexiletine to counteract SCN4A dysfunction.2 However, we lack long-term follow-up studies on flecainide efficiency in patients with PC with homogeneous pheno/genotype. The aim of this study was to assess the responsiveness to flecainide in a large family with classic PC phenotype by electrophysiological and quality of life evaluations.
Patients and methods
The Italian PC family pedigree includes 60 …
MABM and SS contributed equally.
CT and OF contributed equally.
Contributors CT: study concept and design, analysis and interpretation of data, statistical analysis, drafting the manuscript. OF: study concept and design, acquisition of data, analysis and interpretation of data, drafting the manuscript. LL and PDB: patient recruitment and acquisition of data. GC, VT and FT: analysis and acquisition of data. SB and GDI: revising the manuscript for intellectual content. MABM: study supervision, analysis and interpretation of data, revising the manuscript for intellectual content. SS: study concept and design, study supervision, analysis and interpretation of data, drafting and revising the manuscript for intellectual content. TE study concept, analysis and acquisition of data, FN analysis and acquisition of data.
Funding European Funding of Campania Region for neurological and neuromuscular rare diseases.
Competing interests None declared.
Patient consent Obtained.
Ethics approval Ethic Commission of University of Campania ‘Luigi Vanvitelli’, Naples, Italy.
Provenance and peer review Not commissioned; externally peer reviewed.
Correction notice Since this letter was first published online the authors Teresa Esposito and Filomena Napolitano have been added to the author list.
Presented at Preliminary data of this study were presented in the abstract form at the XII International Congress of Neuromuscular Diseases (ICNMD2010), Naples, 17–22 July 2010.