What is muscle dystrophy?
Muscular dystrophy (MD) refers to a group of genetic diseases characterised by progressive weakness and degeneration of the skeletal or voluntary muscles which control movement. The muscles of the heart and some other involuntary muscles are also affected in some forms of MD, and a few forms involve other organs as well.
What is the cause?
The group of diseases called muscular dystrophies (MD) includes many inherited disorders such as:
- Becker's muscular dystrophy
- Duchenne muscular dystrophy
- Facioscapulohumeral muscular dystrophy
- Limb-girdle muscular dystrophy
- Emery-Dreifuss muscular dystrophy
- Myotonic dystrophy
- Myotonia congenita
Duchenne muscular dystrophy is the most common form of MD affecting children, and myotonic MD is the most common form affecting adults. MD can affect people of all ages. Although some forms first become apparent in infancy or childhood, others may not appear until middle age or later.
These disorders are distinguished from each other by the type of inheritance (sex-linked, dominant gene, recessive gene), the age when symptoms appear, and the types of symptoms that develop. Because these are inherited disorders, risks include a family history of muscular dystrophy.
Lambert-Eaton syndrome and myasthenia gravis also have symptoms that may be similar to early stages of some types of muscular dystrophies, so these disorders must be ruled out when muscular dystrophies are diagnosed.
What are the symptoms?
Symptoms vary with the different types of muscular dystrophy. Some types, such as Duchenne muscular dystrophy, are ultimately fatal while other types have associated muscle weakness but cause little disability and are associated with normal life expectancy.
The muscles primarily affected vary, but can be around the pelvis, shoulder, face or elsewhere. The age of onset can vary as well, with more severe subtypes tending to occur earlier in childhood.
- muscle weakness
- progressive frequent falls
- delayed development of muscle motor skills
- problems walking (delayed walking)
- difficulty using one or more muscle groups (the specific muscles
- affected depends on the type of MD)
- eyelid drooping (ptosis)
- mental retardation (only present in some types of MD)
- hypotonia (low muscle tone)
- scoliosis (curved spine)
How is the diagnosis made?
Examination and history help to distinguish the type of MD. Specific muscle groups are affected by different types of MD. Often, there is a loss of muscle mass (wasting), which may be disguised in some types of muscular dystrophy by an accumulation of fat and connective tissue that makes the muscle appear larger (pseudohypertrophy). Joint contractures are common. Shortening of the muscle fibres, fibrosis of the connective tissue and scarring slowly destroy muscle function. Some types of MD involve the heart muscle, causing cardiomyopathy or arrhythmias.
A muscle biopsy may be the primary test used to confirm the diagnosis. In some cases a DNA test from the blood may be sufficient.
- Serum CPK (an enzyme found in muscle) may be elevated
- An EMG (electromyography) may confirm that weakness is caused by destruction of muscle tissue rather than damage to nerves
- An ECG (electrocardiography) to monitor changes in cardiac status.
This disease may also alter the results of the following tests:
- myoglobin - urine/ serum
- LDH (lactate dehydrogenase)
- AST (aspartate aminotransferase)
What is the treatment?
There are no known cures for the various muscular dystrophies. Treatment is aimed at controlling symptoms to maximize the quality of life. Activity is encouraged to the degree tolerated, however, complete inactivity (such as bedrest) can worsen the disease. Physical therapy may help people with this disorder to maintain muscle strength and function. Orthopaedic appliances such as braces and wheelchairs can improve mobility and self-care abilities. In some cases, surgery on the spine or lower extremities may help improve function and slow deterioration.
What is the prognosis?
The outcome varies with the type of muscular dystrophy. All types of MD progressively worsen, but the speed of decline and extent of disability they cause varies widely. Some types are fatal.
What are the complication?
- joint contractures
- permanent, progressive disability
- decreased mobility
- decreased ability to care for self
- mental impairment
- respiratory failure
What is the prevention?
Genetic counselling is advised when there is a family history of muscular dystrophy. Women may be asymptomatic but still be carriers of the gene for the disorder. Duchenne muscular dystrophy can be detected with about 95 percent accuracy by genetic studies performed during pregnancy.