From the Guidelines
The treatment for Steinert's myotonic dystrophy (also called myotonic dystrophy type 1) focuses on managing symptoms as there is currently no cure for this genetic condition. Medications that can help manage myotonia (muscle stiffness) include mexiletine (starting at 150-200 mg twice daily), phenytoin (300 mg daily), and carbamazepine (200 mg 2-3 times daily) 1. For excessive daytime sleepiness, modafinil (200-400 mg daily) or methylphenidate (10-60 mg daily in divided doses) may be prescribed. Cardiac complications often require pacemaker implantation for conduction abnormalities, while respiratory issues may necessitate non-invasive ventilation at night 1. Physical therapy and occupational therapy are essential components of treatment to maintain muscle strength and function, with goals of therapy aimed at regaining muscle strength and function through stretching and strengthening activities 1. Regular monitoring by a multidisciplinary team is crucial, including:
- Cardiac evaluations (annual ECG and echocardiogram)
- Pulmonary function tests
- Ophthalmologic examinations for cataracts Genetic counseling should be offered to patients and families. These treatments aim to improve quality of life by addressing the multisystem effects of the disease, which affects skeletal muscles, heart, brain, eyes, and endocrine system due to abnormal RNA processing caused by CTG repeat expansions in the DMPK gene 1.
Key aspects of management include:
- Early institution of physical therapy to avoid joint contractures and muscle atrophy
- Use of intensive resistance training, which has been found to be beneficial and safe in patients with myotonic dystrophy 1
- Regular assessment of muscle strength, endurance, and functional capacity using validated tools such as the Childhood Myositis Assessment Scale for juvenile cases
- Monitoring of disease activity through muscle enzyme levels, muscle strength testing, and emerging biomarkers like IL-6 and type 1 interferon-regulated genes 1
From the Research
Effective Treatments for Myotonic Dystrophy
- Mexiletine, a class 1b antiarrhythmic sodium antagonist, has been shown to improve clinical myotonia in patients with myotonic dystrophy 2, 3, 4.
- Long-term thiamine treatment has been found to improve motor symptomatology, particularly muscle strength, and patients' activities of daily living in myotonic dystrophy type 1 5.
- A clinical guide for the diagnosis and follow-up of myotonic dystrophy type 1 recommends a multidisciplinary approach, including cardiac and respiratory lifetime follow-up, and genetic counselling 6.
Treatment Outcomes
- Mexiletine treatment has been associated with improved myotonia symptoms in 96% of patients with myotonic dystrophy types 1 and 2, with no clinically relevant cardiac adverse events 3.
- A randomized, double-blind, placebo-controlled trial found that mexiletine improved hand grip myotonia, but had no significant effect on 6-minute walk distance in patients with myotonic dystrophy type 1 4.
- Long-term thiamine treatment has been shown to improve muscle strength and activities of daily living in patients with myotonic dystrophy type 1, with a 25% improvement in Muscular Impairment Rating Scale grade and a 29-44% improvement in Modified Barthel Index 5.