New Classification and Treatment for Myotonic Disorders

Abstract

Myotonia is repetitive firing of muscle action potentials causing prolonged muscle contractions even after mechanical stimulations to the muscles have ceased. Most common myotonic disorder is myotonic dystrophy which is now termed DM1, myotonic dystrophy type 1. In Japan, proximal myotonic myopathy, which is now called DM2 has not been reported. Both DM1 and DM2 have Cl channel abnormality which causes myotonia. Less commonly we encounter Thomsen's disease, and autosomal recessive generalized myotonia (Becker type) which also have a Cl channel abnormality. There are other myotonic disorders related to Na channelopathy which include three disorders: paramyotonia congenita, adynamia episodica hereditaria, and myotonia fluctuans. Myotonia has been treated by various Na channel blockers, mexiletine, phenytoin, and carbamazepine, but they were originally developed for cardiac arrhythmia, or seizure disorders and they have undesirable side effects, weakness. Comprehensive treatment includes myotonia control without reducing the strength, and care for systemic manifestations of DM1.

Dystrophia myotonica type 1 presenting with dysarthria: A case report and literature review

“…Previous studies have indicated that membrane-depressant drugs, including phenytoin sodium and carbamazepine, may alleviate the symptoms of myotonia by promoting the activity of sodium pumps, leading to a reduction in intramembranous sodium concentration and an increase in resting membrane potential (30,31). In addition, physical training may aid the maintenance of normal muscle functions (22).…”

Nonsustained ventricular tachycardia does not affect the prognosis of neuromuscular diseases: A preliminary and retrospective study

“…Regarding the limitations on this study, first of all, this was a singlecenter, retrospective study, and bias could be inherent in this type Second, this study included many types of NMDs. For example, although it is known that myotonic dystrophy involves channel abnormalities and develops into arrhythmias, 21 this pathogenetic mechanism is not always applicable to other NMDs. Third, our study had a diagnostic limitation of only single recording of Holter ECG for NSVT.…”

Identification and Characterization of DM1 Patients by a New Diagnostic Certified Assay: Neuromuscular and Cardiac Assessments

“…DM1 is the most common adult form of muscular dystrophy with a prevalence of 1 in 8000, characterized by progressive muscle weakness and atrophy, myotonia, early-onset cataracts and multiple organ involvement [4, 5]. The cardiac conduction system is selectively involved in DM1, and severe cardiac arrhythmias and respiratory insufficiency are the most frequent causes of death in these patients [6].…”