Muscular dystrophy
Muscular dystrophy: Excerpt from Professional Guide to Diseases (Eighth Edition)
Muscular dystrophy is actually a group of congenital disorders characterized by progressive symmetrical wasting of skeletal muscles without neural or sensory defects. Paradoxically, these wasted muscles tend to enlarge because of connective tissue and fat deposits, giving an erroneous impression of muscle strength. The main types of muscular dystrophy are Duchenne’s (pseudohypertrophic), Becker’s (benign pseudohypertrophic), facioscapulohumeral (Landouzy-Dejerine), and limb-girdle dystrophy.
The prognosis varies. Duchenne’s muscular dystrophy generally strikes during early childhood and usually results in death by age 20. Patients with Becker’s muscular dystrophy typically live into their 40s. Facioscapulohumeral and limb-girdle dystrophies usually don’t shorten life.
Causes and incidence
Muscular dystrophy is caused by various genetic mechanisms. Duchenne’s and Becker’s muscular dystrophies are X-linked recessive disorders. Both result from defects in the gene coding for the muscle protein dystrophin; the gene has been mapped to the Xp21 locus.
The incidence muscular dystrophy is about 1 in 651,450 persons in the United States. Duchenne’s and Becker’s muscular dystrophies affect males almost exclusively.
Facioscapulohumeral dystrophy is an autosomal dominant disorder. Limb-girdle dystrophy is usually autosomal recessive. These two types affect both sexes about equally.
Signs and symptoms
Although all four types of muscular dystrophy cause progressive muscular deterioration, the degree of severity and age of onset vary.
Duchenne’s muscular dystrophy begins insidiously, between ages 3 and 5. Initially, it affects leg and pelvic muscles but eventually spreads to the involuntary muscles. Muscle weakness produces a waddling gait, toe walking, and lordosis. Children with this disorder have difficulty climbing stairs, fall down often, can’t run properly, and their scapulae flare out (or “wing”) when they raise their arms. Calf muscles especially become enlarged and firm. Muscle deterioration progresses rapidly, and contractures develop. Some have abrupt intermittent oscillations of the irises in response to light (Gower’s sign). Usually, these children are confined to wheelchairs by ages 9 to 12. Late in the disease, progressive weakening of cardiac muscle causes tachycardia, electrocardiogram abnormalities, and pulmonary complications. Death commonly results from sudden heart failure, respiratory failure, or infection.
Signs and symptoms of Becker’s muscular dystrophy resemble those of Duchenne’s muscular dystrophy, but they progress more slowly. Although symptoms start around age 5, the patient can still walk well beyond age 15 — sometimes into his 40s.
Facioscapulohumeral dystrophy is a slowly progressive and relatively benign form of muscular dystrophy that commonly occurs before age 10 but may develop during early adolescence. Initially, it weakens the muscles of the face, shoulders, and upper arms but eventually spreads to all voluntary muscles, producing a pendulous lower lip and absence of the nasolabial fold. Early symptoms include the inability to pucker the mouth or whistle, abnormal facial movements, and the absence of facial movements when laughing or crying. Other signs consist of diffuse facial flattening that leads to a masklike expression, winging of the scapulae, the inability to raise the arms above the head and, in infants, the inability to suckle.
Limb-girdle dystrophy follows a similarly slow course and commonly causes only slight disability. Usually, it begins between ages 6 and 10; less commonly, in early adulthood. Muscle weakness first appears in the upper arm and pelvic muscles. Other symptoms include winging of the scapulae, lordosis with abdominal protrusion, waddling gait, poor balance, and the inability to raise the arms.
Diagnosis
Diagnosis depends on typical clinical findings, family history, and diagnostic test findings. If another family member has muscular dystrophy, its clinical characteristics can indicate the type of dystrophy the patient has and how he may be affected.
Electromyography typically demonstrates short, weak bursts of electrical activity or high-frequency, repetitive waxing and waning discharges in affected muscles. Muscle biopsy shows variations in the size of muscle fibers and, in later stages, shows fat and connective tissue deposits; dystrophin is absent in Duchenne’s dystrophy and diminished in Becker’s dystrophy. Serum creatine kinase is markedly elevated in Duchenne’s, but only moderately elevated in Becker’s and facioscapulohumeral dystrophies.
Immunologic and molecular biological assays available in specialized medical centers facilitate accurate prenatal and postnatal diagnosis of Duchenne’s and Becker’s muscular dystrophies and are replacing muscle biopsy and elevated serum creatine kinase levels in diagnosing these dystrophies. These assays can also help to identify carriers.
Treatment
No treatment stops the progressive muscle impairment of muscular dystrophy. However, orthopedic appliances, exercise, physical therapy, and surgery to correct contractures can help preserve the patient’s mobility and independence. Prednisone improves muscle strength in patients with Duchenne’s.
Special considerations
Comprehensive long-term care and follow-up, patient and family teaching, and psychological support can help the patient and his family deal with this disorder.
❑ When respiratory involvement occurs in Duchenne’s muscular dystrophy, encourage coughing, deep-breathing exercises, and diaphragmatic breathing. Teach parents how to recognize early signs of respiratory complications.
❑ Encourage and assist with active and passive range-of-motion exercises to preserve joint mobility and prevent muscle atrophy.
❑ Advise the patient to avoid long periods of bed rest and inactivity; if necessary, limit TV viewing and other sedentary activities.
❑ Refer the patient for physical therapy. Splints, braces, surgery to correct contractures, trapeze bars, overhead slings, and a wheelchair can help preserve mobility. A footboard or high-topped sneakers and a foot cradle increase comfort and prevent footdrop.
❑ Because inactivity may cause constipation, encourage adequate fluid intake, increase dietary bulk, and obtain an order for a stool softener. The patient is prone to obesity due to reduced physical activity; help him and his family plan a low-calorie, high-protein, high-fiber diet.
❑ Always allow the patient plenty of time to perform even simple physical tasks because he’s likely to be slow and awkward.
❑ Encourage communication between the patient’s family members to help them deal with the emotional strain this disorder produces. Provide emotional support to help the patient cope with continual changes in body image.
PEDIATRIC TIP Help the child with Duchenne’s muscular dystrophy maintain peer relationships and realize his intellectual potential by encouraging his parents to keep him in a regular school as long as possible.
❑ If necessary, refer adult patients for counseling. Refer those who must acquire new job skills for vocational rehabilitation. (Contact the Department of Labor and Industry in your state for more information.) For information on social services and financial assistance, refer these patients and their families to the Muscular Dystrophy Association.
❑ Refer the patient’s family members for genetic counseling.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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