Muscular Dystrophies:
Definition
Limb-girdle muscular dystrophies include at least 10 different inherited disorders that initially affect the muscles around the shoulder girdle and the hips. These diseases are progressive and may involve other muscles over a period of time.
Causes, incidence, and risk factors
This is a large group of genetic diseases featuring muscle weakness and wasting (muscular dystrophy). Most are inherited in an autosomal recessive manner (both parents must have the defective gene for a child to inherit it), but some are autosomal dominant (only one parent needs to carry the bad gene to affect the child). For some of these conditions, the defective gene has been discovered, but for others, the gene is not yet known.
Typically, onset of pelvic muscle weakness (difficulty standing from a sitting position without using arms, difficulty climbing stairs) starts in childhood to young adulthood. Later there is the onset of shoulder weakness with progression to significant loss of mobility or wheelchair dependence over the next 20-30 years.
An important risk factor is having a family member with muscular dystrophy.
Symptoms
- Muscle weakness in pelvis, hips, upper legs, shoulders
- Loss of muscle mass in the same areas, thinning of those body parts
- Low back pain
- Abnormal, sometimes waddling, gait while walking
- Later in disease, there can be facial muscle weakness
- Later in the disease, muscles of the lower legs, feet, lower arms, and hands can become weak
- Late in the disease, there can be contractures of joints (they become fixed in a contracted position)
- Palpitations or passing out spells can be caused by abnormal heart rhythms
- Sometimes the calves will look large and muscular (pseudohypertrophy), but they are actually not strong
Signs and tests
- Normal muscle biopsy for dystrophin (the protein that is defective in the more common Duchenne muscular dystrophy)
- Electromyogram (EMG) testing shows a pattern called myopathy, sick and dying muscle fibers
- High blood creatine kinase levels
- Muscle biopsy shows degenerating muscle with splitting of muscle fibers and presence of cells of the immune system (phagocytes), which are not normally present
- In some less common muscular dystrophies, the heart may show weakness on echocardiogram (heart failure) or abnormal rhythm on ECG
Each type of LGMD has a different range of symptoms (see table 3). The symptoms can even vary between individuals with the same type of LGMD. The age of onset of symptoms varies tremendously and can range from infancy to adulthood. The most common symptom of LGMD is muscle weakness and deterioration involving the muscles around the hips and shoulders. The disorder progresses at a different rate in different people. The progression and extent of muscle deterioration cannot be predicted, although individuals with an onset of the disorder in adulthood may have a slower progression and milder symptoms.
The first noticeable symptom of LGMD is often a "waddling" gait due to weakness of the hip and leg muscles. Difficulties in rising from a chair or toilet seat and difficulties in climbing stairs are common. Eventually walking may become so difficult that a wheelchair or scooter is necessary for locomotion. Enlargement or a decrease in size of the calf muscles can also be seen. Contractures and muscle cramps are experienced by some individuals with LGMD. The limited mobility associated with LGMD can result in muscle soreness and joint pain.
Lifting heavy objects, holding the arms outstretched and reaching over the head can become difficult because of weaknesses in the shoulder muscles. Some individuals with LGMD may even eventually have difficulties swallowing and feeding themselves. Sometimes the back muscles can become weakened and result in scoliosis (curvature of the spine).
LGMD can occasionally result in a weakening of the heart muscles and/or the respiratory muscles. Some people may experience a weakening of the heart muscles called a cardiomyopathy. Others may develop a conduction defect, an abnormality in the electrical system of the heart that regulates the heartbeat. A weakening of the muscles necessary for respiration can cause breathing difficulties. LGMD does not affect the brain and the ability to reason and think. Individuals with LGMD also maintain normal bladder and bowel control and sexual functioning.
Treatment
There are no known treatments that directly reverse the muscle weakness. Gene therapy may become available in the future. Supportive treatment can decrease the complications of the disease.
Prognosis
This is a large group of related but distinct diseases. In general, it is expected that there will be slow progression of weakness, which worsens in affected muscles, spreads, and progresses further.
Heart muscle weakness and the tendency to have abnormal electrical activity of the heart can increase the risk of palpitations, fainting and sudden death. Most patients with this group of diseases live into adulthood, but do not reach their full life expectancy.
Complications
- Progressive weakness, which results in requiring a wheelchair
- Difficulties with activities of daily living due to shoulder weakness
- Contractures due to decreased muscle movements and joint use
- Abnormal heart rhythms
Additional Information