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School of Medicine
Myotonic Muscular Dystrophy
Myotonic muscular dystrophy is a common multi-system disorder that affects the skeletal muscles (the muscles that move the limbs and trunk) as well as smooth muscles (the muscles that control the digestive system) and cardiac muscles of the heart. Symptoms of myotonic dystrophy might include difficulty releasing one’s grip (myotonia), weakness of muscles in the hands and feet, difficulty swallowing and abnormal heart rhythms. Non-muscle symptoms may also include learning difficulties, daytime sleepiness, infertility and early cataracts. There are two known forms of this disease (Myotonic Dystrophy Type 1 and Myotonic Dystrophy Type 2). Both are caused by abnormal expansions of repeated areas of genes. In Myotonic Dystrophy Type 1, the repeat expansion enlarges with each generation, frequently leading to earlier onset and increased severity of symptoms with each affected generation. Myotonic Dystrophy Type 1 therefore frequently affects children in families with this disorder.
The diagnosis of Myotonic Dystrophy is based on the clinical history, including a family history, physical examination and supporting laboratory studies. Supporting laboratory studies may include blood work, electrodiagnostic testing (EMG) and muscle biopsy. Muscle biopsy is often helpful to determine if weakness is caused by muscular dystrophy, an inherited disorder, or by other acquired causes of muscle degeneration such as from inflammation or toxic exposure. A definitive diagnosis is usually possible by a blood test to determine the specific genetic defect responsible for myotonic dystrophy type 1 or type 2. Our genetics counselor will carefully review the history of disease with each patient, discuss the principles of inheritance and help weigh risks and benefits of genetic testing in the patient, and if appropriate in various family members.
Treatment of Myotonic dystrophy is by a multidisciplinary team. A neurologist oversees the various needs of the patient and directs care. The neurologist may recommend that myotonia, the inability to relax muscles, be treated with a drug such as mexiletine. An EKG to look at the heart rhythm, and frequently an echocardiogram to look at heart function, will be performed. A test of lung function will also be performed. Depending on the neurologist’s findings and results of these tests, a referral to other Johns Hopkins specialists who also have expertise in myotonic dystrophy, including cardiologists, pulmonologists and ophthalmologists will be recommended for additional treatment.
Specialists in rehabilitation medicine are present during the clinic time to meet with patients and provide individualized exercise and stretching programs for the treatment of weakness and contractures. Also on the same day, the patient will be evaluated for the need for splints and orthotics to help with hand or foot function. Muscular Dystrophy Association liaisons are on hand to address equipment needs as well as social and financial issues.
Myotonic dystrophy is a complex disorder that affects many organ systems throughout the body. Most people with myotonic dystrophy can lead full, successful lives. This requires the involvement of a group of health care professionals with experience and dedication to the disease as is found at Johns Hopkins.
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