Inflammatory Myopathies - Questions and Answers Print E-mail

Question: What are inflammatory myopathies?
Answer: Inflammatory myopathies are a group of muscle diseases that are characterized by inflammation and degeneration of skeletal muscle fibers.

Question: Question: What is the cause of inflammation in these disorders?
Answer: The provocative antigene is not identified precisely yet. Viral infection is suggested Pathologically, inflammatory cells invade and destroy non-necrotic muscle fibers The invaded muscle fibers are thought to be defective, or carry an altered molecule, that render them foreign to the immune system. Eventually, this results in muscle destruction.

Question: What are the signs of inflammatory myopathies?
Answer: The initial presentation is usually due to difficulty rising from a chair, getting out the car, climbing stairs, or lifting the arms above the shoulder levels. Also, breathing and swallowing difficulties are common. Weakness usually involves the proximal muscles symmetrically.

Question: How is the diagnosis made?
Answer: The clinical picture provides the clinician with clues to the diagnosis. Other testing that helps to establish the diagnosis includes CPK measurement, EMG, and muscle biopsy. Electromicroscopy may be useful in certain situations, in particular to confirm the diagnosis of inclusion body myositis.

Question: How many types of inflammatory muscle diseases are there?
Answer: Inflammatory muscle disease can be:

1.

Primary, where the immunological response is primarily directed toward the muscle tissue or the intramuscular blood vessels. This group includes dermatomyositis, polymyositis and inclusion body myositis,
2. Secondary where the inflammation is a secondary process to an underlying disorder such as sarcoidosis or cysticercosis.

Question: What are the features of dermatomyositis?
Answer: Dermatomyositis is an inflammatory muscle disease characterized by symmetrical proximal weakness in the arms and legs and a distinctive skin rash that occurs usually around the eyelids, the cheeks, the bridge of the nose, on the back or upper chest, elbows, knees and knuckles. The rash is usually dusky and patchy. Calcified subcutaneous nodules are common in children. The skin rash usually precedes the muscle weakness, which develops over weeks to months. The weakness usually starts with the proximal muscles, including the neck muscles, hip, trunk and shoulder muscles, leading to difficulty in standing up from a chair or holding the arms up.

Question: Is pain common in dermatomyositis?
Answer: About 25% of adults with dermatomyositis complain of muscle pain and about 50% of children with this disease report muscle pain and tenderness.

Question: What is the target age group for dermatomyositis?
Answer: Dermatomyositis can occur in any age group from childhood to adulthood. It is more common in females than males.

Question: What is the treatment for dermatomyositis?
Answer: High-dose prednisone, either intravenously or orally, and cytotoxic medications such as azathioprine, cyclophosphamide, methotrexate, and more recently mycophenolate, are usually effective in controlling the disease. However, unfortunately, these medications are associated with side-effects after prolonged use. Patients who fail prednisone may respond well to intravenous gamma globulin.

Question: What are the characteristic features of polymyositis?
Answer: Proximal muscle weakness that usually affects the arm and leg muscles, swallowing difficulty, and shortness of breath are common. They are more often in polymyositis than dermatomyositis. Muscle pain involves about one-third of the patients, but it is rarely the presenting complaint. Polymyositis rarely affects people under age 20. Again, the disease is more common in women. High doses of prednisone have been effective for treatment. Other immunosuppressants are also useful, in particular the steroid-sparing agents. Again, people who do not respond to prednisone may respond to intravenous gamma globulin.

Question: What are the characteristic features of inclusion body myositis (IBM)?
Answer: IBM is very similar to polymyositis, except that it is more common in males after age 50. As a matter of fact, it is the most common muscle disease that starts after age 50. The disease is very gradual and occurs over months to years. The diagnosis is usually made late due to the slow progression of the disease and it is commonly confused with Lou Gehrig disease. Again, the weakness affects both proximal and distal muscles.

Question: What are the characteristic and clinical features of IBM?
Answer: Unlike the other inflammatory muscle diseases, the wrist flexors and finger flexors, and the quadriceps are more severely affected than the other proximal muscles. Inclusion body myositis is one of the muscle diseases that affect both distal and proximal muscles. Other muscle diseases that affect the distal musculature, besides the proximal one, are myotonic dystrophy and hereditary distal myopathies. Facial weakness and swallowing difficulty are common. A hereditary form of the disease is also identified.

Question: What is the treatment for inclusion body myositis?
Answer: Unfortunately, there is no successful treatment yet. Favorable response to IVIG has been reported. Other avenues are being explored. Physical therapy may be helpful to maintain mobility.

Question: What are the characteristic pathological features of inflammatory myopathies?
Answer: Infiltration of the muscle tissue with mononuclear inflammatory cells is the hallmark of the diagnosis.

Question: What are the pathological features of dermatomyositis?
Answer: Dermatomyositis is, pathologically, not exactly a muscle disease. It is rather a disease that affects the intramuscular blood vessels. Antibodies against the endothelial surface of the intramuscular blood vessels have been identified and are considered to be the antigenic culprit. The characteristic pathological features include perifascicular atrophy, which is defined as atrophy of 3-5 layers of the muscle fibers adjacent to the margin of the fascicles. The margins of the fascicles are considered to be the watershed area of the muscle fascicle and obliteration of the intramuscular blood vessels is reflected first as a wasting of these layers.

Further characterization of the inflammatory infiltrates has revealed that it consists mainly of CD4 lymphocytes, which is usually associated with a humeral immunological response. Dermatomyositis is a disease that is caused by the disturbance of the humeral immunity rather than a cell-mediated immunity, as is the case with polymyositis and inclusion body myositis.

Question: What are the pathological features of polymyositis?
Answer: Invasion of non-necrotic muscle fibers with CD8 lymphocytes is the main feature of polymyositis.

Question: What are the characteristic pathological features of IBM?
Answer: Again, invasion of non-necrotic muscle fibers with CD8 lymphocytes is the main feature. In addition, the disease is characterized by the presence of cytoplasmic vacuoles. These vacuoles are surrounded by a red rim when stained with a modified Gomori trichrome stain. This is why they are called red-rimed vacuoles. The presence of intracellular amyloid deposits is also demonstrated. Both cytoplasmic and nuclear inclusion bodies are characteristic and they are usually located adjacent to the mentioned vacuoles.
 
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