Muscular Dystrophy - types, symptoms and treatment
Muscular Dystrophy - The collective term for a group of GENETIC DISORDERS of the MUSCLE resulting in progressive weakness. Most types of muscular dystrophy arise from a deficiency of the protein dystrophin, which is essential for skeletal (striated) muscle cell integrity and function. Without it the skeletal muscles deteriorate and movement becomes difficult or impossible. About 50,000 Americans have muscular dystrophy. The three most common of the nine major types of muscular dystrophy are Duchenne’s muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic muscular dystrophy.
Duchenne’s muscular dystrophy
Duchenne’s is an X-linked recessive MUTATION affecting the dystrophin GENE. As such, it nearly exclusively affects boys. Symptoms begin to appear in early childhood with characteristic postures and gait. Progression is steady, and most boys who have Duchenne’s lose the ability to walk by about age 12. The skeletal muscles of the upper chest become involved in ADOLESCENCE, affecting BREATHING. Duchenne’s is usually fatal before age 20.
A milder presentation of similar symptoms and pattern of progression with a later age of onset (late childhood or early adolescence) is Becker’s muscular dystrophy. Though the course of the disease is ultimately fatal, most who have it live into their 30s. Treatment is primarily supportive, with PHYSICAL THERAPY to help preserve muscle STRENGTH and function. CORTICOSTEROID MEDICATIONS may improve symptoms.
Facioscapulohumeral muscular dystrophy
An adult-onset type of muscular dystrophy, facioscapulohumeral muscular dystrophy affects men and women equally. Symptoms first appear as weakness in the muscles of the face and shoulder girdle (upper arms and shoulders). The shoulders often “wing” outward. Over the course of the disease, muscle weakness moves downward through the body though the lower arms are usually the last affected. Symptoms are mild enough in about half of those who have this form of muscular dystrophy to permit fairly normal function and mobility throughout life. In others, symptoms may affect swallowing and mobility.
Myotonic muscular dystrophy
In myotonic muscular dystrophy the muscles lose the ability to relax after contraction, causing them to become stiff. Myotonic muscular dystrophy is the most common type of adult-onset muscular dystrophy and affects men and women equally. The cause is a mutation in the gene that encodes for myotonica protein kinase. Other gene mutations may also contribute. Though progression is usually slow, myotonic muscular dystrophy affects other body systems as well. Cataracts and diabetes are common.
| MAJOR TYPES OF MUSCULAR DYSTROPHY | ||
|---|---|---|
| Type of Muscular Dystrophy | Key Characteristics | Inheritance Pattern |
| Duchenne’s | most common type affects primarily muscles of the upper arms, upper legs, and pelvic girdle first symptoms usually appear between ages 2 and 6 |
X-linked recessive |
| myotonic | affects primarily muscles of the face and neck, hands, and feet gastrointestinal, cardiac, EYE, neurologic, and endocrine involvement later in the disease first symptoms appear in adulthood |
autosomal dominant |
| Becker’s | affects primarily muscles of the upper arms, upper legs, and pelvic girdle very similar to Duchenne’s with milder symptoms symptoms begin in late childhood or early ADOLESCENCE |
X-linked recessive |
| limb-girdle | affects primarily the muscles of the pelvic girdle and shoulder girdle symptoms begin in late adolescence or early adulthood |
autosomal recessive or autosomal dominant |
| facioscapulohumeral | affects primarily the muscles of the face, neck, and shoulders symptoms begin in late adolescence or early adulthood |
autosomal dominant |
| congenital | affects all skeletal muscles often affects the CENTRAL NERVOUS SYSTEM, causing seizures symptoms are present at birth |
autosomal recessive |
| oculopharyngeal | affects the muscles of the eyelids and THROAT symptoms begin in middle to late adulthood |
autosomal dominant |
| distal | affects the forearms, hands, lower legs, and feet symptoms begin in adulthood |
autosomal recessive or autosomal dominant |
| Emery-Dreifuss | affects primarily the shoulders, upper arms, pelvis, and lower legs symptoms typically appear first as contractures, then weakness symptoms begin in late childhood or early adolescence |
X-linked recessive |
Symptoms of Muscular Dystrophy and Diagnostic Path
In most forms of muscular dystrophy, the primary symptoms are muscle weakness and disturbances of posture and gait (walking style). The diagnostic path begins with detailed PERSONAL HEALTH HISTORY and family health history. Because muscular dystrophies are inherited disorders, the family health history is particularly important. A comprehensive NEUROLOGIC EXAMINATION identifies the specific symptoms, which helps narrow the diagnosis. BLOOD tests may show excessive proteins that indicate muscle destruction. Each type of muscular dystrophy has fairly characteristic patterns of symptoms. Muscle biopsy shows damage to the muscle cells.
Muscular Dystrophy Treatment Options and Outlook
Treatment for all types of muscular dystrophy is primarily supportive. Physical therapy, braces, orthotics, and mobility aids extend the ability to walk and function independently. Corticosteroid medications slow the progression of symptoms in some types of muscular dystrophy, notably Duchenne’s. Though all types of muscular dystrophy are lifelong, muscular dystrophy is not necessarily fatal. Many people with milder types of the disease live normal life expectancy with relative independence.
Risk Factors and Preventive Measures
Muscular dystrophy is always inherited, so the key risk factor is family history. People who have muscular dystrophy or family history of muscular dystrophy should consider GENETIC COUNSELING to aid in FAMILY PLANNING decisions. There are no measures known to prevent muscular dystrophy, though research holds hope for GENE THERAPY that can someday correct the mutations that cause the disease.
See also CATARACT; MYOPATHY.
