Myopathy is a type of muscular disease, characterized by improper functioning of the muscle fibers, causing muscular weakness. It is a disease of the muscles, which can be either neuromuscular, or musculoskeletal in nature.
Onset of muscular weakness of the proximal muscles is the classical symptom of myopathy. This is followed by development of muscle cramps and pain. In majority of the cases, myopathy significantly affects the pelvic girdle muscles, than the muscles of the shoulder girdle.
Myopathies, that occur due to inflammatory disease, such as myositis, cause development of weakness in the fingers and quadriceps. Such a type of condition, majorly affects the older population. Affected individuals may also suffer from fever. In addition, other signs and symptoms include the following:
- Muscle Swelling
These almost always cause weakness and can cause muscle swelling and pain. [ohsu.edu]
Myalgia, muscle weakness, muscle swelling, myoglobinuria (cola colored urine with raised serum and urine myoglobin levels) and a marked elevation in serum CK (between 10 and 100 × ULN) are the usually seen. [hiv.imedpub.com]
- Limb Weakness
A 47-year-old man with liver cirrhosis developed limb weakness after liver transplantation. The patient had a Medical Research Council sum score of 2 weeks post-liver transplantation with marked proximal limb weakness. [ncbi.nlm.nih.gov]
Patients present with axial hypotonia, myopathic facies with fatigable ptosis, feeding difficulties, delayed gross motor development and proximal limb weakness with a RYR1-related typical pattern of muscle involvement (i.e. severe involvement of the soleus [orpha.net]
The following tests are employed for diagnosing several types of myopathies:
- Laboratory tests: These are done for determining muscle damage, and levels of liver enzymes, aldolase, creatine phosphokinase and lactate dehydrogenase. Tests should also be done, to determine underlying disease conditions, and involvement of certain autoantibodies, in causation of myopathy.
- Forearm test: This test is useful, in determining the presence of metabolic myopathy. Ischemic forearm test is performed, by analyzing the levels of serum ammonia, and lactate from forearm.
- Electromyography (EMG): An electromyogram is carried out, to determine the electrical activity of the muscles and nerves. This study gives insight into the severity, and duration of the disease condition. EMG should however be done, along with other tests, because in case of mild myopathies, the test may reveal normal results.
- Muscle biopsy: Biopsy of the deltoid muscles, or biceps, is done to diagnose the condition of myopathy. Muscles that have experienced severe weakness, and those where EMG test has been carried out, should not be considered for biopsy. Therefore, samples from biceps and deltoid muscles of the affected individuals should be taken for biopsy to get appropriate results .
- Treatment depends on the severity of the symptoms, and type of myopathy, that has set in. In cases, where there are signs of associated complications, hospital admission, along with methods to stabilize the condition of patient is the goal.
- Development of periodic paralysis in patients with myopathy, is a common scenario. In such patients, the swallowing ability is not affected, and oral supplementation of potassium is indicated, if hypokelemia has set in. The paralytic attack should get corrected within 24 hours .
- Patients, who have developed hyperkalemic periodic paralysis, often require no treatment. The attacks are brief, and get resolved on their own. In case when they do not, then carbohydrate load can be helpful in decreasing the intensity of the attacks. In order to bring down the levels of potassium, glucose and insulin have to be administered .
The prognosis of myopathy is favorable, if the underlying condition can be successfully treated, such as in cases of endocrine myopathies. Congenital myopathy has a poor prognosis rate, and children gradually fall prey to muscular weakness, as they grow up. The myopathies that develop later in life have a much better prognosis, than the congenital type .
Myopathy can be acquired or inherited in nature. The following are the various causative factors, which can cause such a type of muscular disease :
It has also been estimated, that the worldwide prevalence of inheritable myopathy is about 14%. In US, the incidence of Duchenne and Becker MD is about 1 in every 3300 boys. Inflammatory myopathies occur in about 5 to 10 individuals per 100,000 people. This condition is particularly common in women than men.
The mortality and morbidity profile of myopathy, depends on the severity and causative factors. In case of severe weakness, the individual can suffer from respiratory failure, causing death. Polynesians are at an increased risk of contracting the disease condition .
Inherited myopathy, or the congenital form, progresses slowly, over a period of several years. Factors such as infections, genetic abnormalities, inflammation, toxins and electrolyte imbalances, can cause acute or chronic myopathies to set in. These factors cause significant disruption of metabolic processes, along with the structural integrity of the muscle cells. Such sequence of events can cause muscle weakness to develop, which in more advanced and severe cases, can lead to periodic paralysis .
Not all forms of myopathy can be prevented. Only those that have genetic links can be prevented, through counseling imparted in the early stages. Prenatal diagnosis for testing of genetic abnormalities in the fetus, can also prevent the development of congenital myopathies. Inflammatory myopathies that develop as a result of infectious agents cannot be always prevented, as it is almost impossible to predict the onset of such a type of condition .
Muscle weakness sets in as a result of abnormalities, which occur in the cell structure of the muscles and metabolism. Myopathy can be classified under two categories, acquired and inherited. In many circumstances, the condition can also significantly affect the cardiac muscles, as a result of which dilated cardiomyopathy or hypertrophic cardiomyopathy can set in .
- Definition: Myopathy is a muscular disease, causing weakening of the muscle fibers, which gradually leads to muscle weakness to develop. There are several types of myopathies, each with a different etiology, and triggering factors. Pain, weakness, spasms, and cramps of the affected muscles, are typical features of myopathy.
- Cause: Myopathy can be caused due to infections, underlying disease condition, heredity, genetic abnormalities, exposure to toxins and inflammatory diseases. Abnormalities in the cellular component, dehydration and glycogen storage disease, are some of the causative factors, which can lead to development of myopathy.
- Symptoms: Muscular weakness, along with pain and cramps, are the major symptoms experienced by affected individuals. In addition, individuals also experience difficulty, in getting up from sitting position, climbing stairs, raising forearm to change bulb, and combing hair. Individuals with myopathy also pass dark colored urine, mainly after carrying out intense exercise.
- Diagnosis: Diagnosis of myopathy includes laboratory tests to determine levels of creatine phosphokinase, lactate dehydrogenase, aldolase and liver enzymes. In addition to these, Electromyography (EMG), forearm test and muscle biopsy are also required.
- Treatment: The underlying cause of the disease is treated, to effectively manage the symptoms. Onset of periodic paralysis, with either hyperkalemia or hypokalemic is a common feature. Emergency care to normalize the levels of potassium, along with management of paralysis is advocated.
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