From the Guidelines
Myotonic dystrophy patients should receive regular cardiac monitoring and multidisciplinary care to manage their condition and prevent life-threatening complications, such as cardiac arrhythmias and respiratory failure, as recommended by the American Heart Association 1.
Key Characteristics of Myotonic Dystrophy
Myotonic dystrophy is a genetic disorder that affects multiple body systems, including the heart, eyes, endocrine system, and brain. There are two recognized forms of myotonic dystrophy: type 1 (DM1) and type 2 (DM2), both of which are inherited in an autosomal dominant manner 1.
- DM1 is caused by expansion of an unstable CTG trinucleotide repeat in the 3′ untranslated region of the DMPK gene.
- DM2 is caused by expansion of a CCTG repeat in intron 1 of CNBP.
Clinical Manifestations and Management
Symptoms of myotonic dystrophy typically include:
- Facial weakness
- Drooping eyelids
- Difficulty swallowing
- Cataracts
- Cardiac conduction abnormalities
- Excessive daytime sleepiness Treatment is supportive and symptom-based, including:
- Physical therapy to maintain muscle strength
- Cardiac monitoring for arrhythmias
- Medications like mexiletine to manage myotonia Genetic counseling is essential for affected individuals and their families due to the hereditary nature of the condition and the phenomenon of anticipation, where symptoms may worsen in subsequent generations 1.
Importance of Multidisciplinary Care
Regular multidisciplinary care involving neurologists, cardiologists, pulmonologists, and other specialists is crucial for managing this complex, progressive condition and maintaining quality of life. Cardiac manifestations are present in approximately 80% of DM1 patients, and the risk of developing cardiac disease is higher in younger patients 1.
- Dilated cardiomyopathy has been reported, but progressive atrioventricular or intraventricular conduction defects and tachyarrhythmias are the most life-threatening forms of cardiac complications.
- Respiratory complications and cardiac arrhythmias are the most frequent primary causes of death in DM1.
From the Research
Myotonic Dystrophy Overview
- Myotonic dystrophy is a progressive multisystem genetic disorder with clinical and genetic features in common, including myotonia, which is a core clinical feature 2.
- Myotonic dystrophy type 1 is the most prevalent muscular dystrophy in adults and has a wide phenotypic spectrum, while myotonic dystrophy type 2 tends to cause a milder phenotype with later onset of symptoms 2.
Treatment and Management
- Mexiletine, an antagonist of voltage-gated sodium channels, is a recommended antimyotonic agent in the nondystrophic myotonias and has been shown to be effective in reducing myotonia symptoms in myotonic dystrophy types 1 and 2 3, 4, 5.
- A study demonstrated that 96% of patients reported some improvement in myotonia symptoms with mexiletine treatment, with no clinically relevant cardiac adverse events associated with long-term use 4.
- Consensus-based care recommendations for adults with myotonic dystrophy type 1 have been developed, including a 4-page Quick Reference Guide and a comprehensive document providing clinical care recommendations for 19 discrete body systems and/or care considerations 6.
Efficacy and Safety of Mexiletine
- Mexiletine has been shown to be safe and effective in reducing myotonia symptoms in myotonic dystrophy types 1 and 2, with significant reduction in grip relaxation time and no serious adverse events or prolongation of the PR or QTc intervals or of QRS duration 5.
- Long-term use of mexiletine has been demonstrated to be well-tolerated and effective in reducing myotonia symptoms, with no clinically relevant cardiac adverse events 4.