polymyositis

What is polymyositis?

Polymyositis is a disease of muscle featuring inflammation of the muscle fibers. The cause of the disease is not known. It begins when white blood cells, the immune cells of inflammation, spontaneously invade muscles. The muscles affected are typically those closest to the trunk or torso. This results in weakness that can be severe. Polymyositis is a chronic illness with periods of increased symptoms, called flares or relapses, and minimal or no symptoms, known as remissions.

Polymyositis is slightly more common in females. It affects all age groups, although its onset is most common in middle childhood and in the 20s. Polymyositis occurs throughout the world. Polymyositis can be associated with skin rash and is then referred to as "dermatomyositis." It also can affect other areas of the body and is, therefore, referred to as a systemic illness. Occasionally, it is associated with cancer or with other diseases of connective tissue (see systemic lupus erythematosus, scleroderma and rheumatoid arthritis).

What causes polymyositis?

To date, no cause of polymyositis has been isolated by scientific researchers. There are indicators of heredity (genetic) susceptibility that can be found in some patients. There is indirect evidence of infection by a virus that has yet to be identified in a form of polymyositis that is particularly resistant to treatment, called inclusion body myositis. This form of polymyositis is diagnosed by the pathologist, a physician specialist who interprets the microscope findings of muscle tissue. The muscle tissue in this form of polymyositis displays clear areas within the muscle cells (called vacuoles) when viewed under the magnification of a microscope.

Researchers from Sweden at the national meeting of the American College of Rheumatology in 2007 reported their findings that T-cells of the immune system in some polymyositis or dermatomyositis patients reacted against cytomegalovirus (CMV) and that detectable antibodies against CMV were present. Their conclusion was that there may be subsets of patients who develop their disease, in part, because of infection with this particular virus.

Aside from diseases with which polymyositis can be associated (as mentioned above), many other diseases and conditions can mimic polymyositis. These include nerve-muscle diseases (such as muscular dystrophies), drug toxins (such as alcohol, cocaine, steroids, colchicine, hydroxychloroquine, and cholesterol-lowering drugs, called statins), metabolic disorders (where muscle cells are unable to process chemicals normally), hormone disorders (such as abnormal thyroid), calcium and magnesium conditions, and infectious diseases (such as influenza virus, AIDS, streptococcus and Lyme bacteria, pork tapeworm and schistosomiasis).

Complications

Possible complications of polymyositis include:

• Difficulty swallowing. If the muscles in your esophagus are affected, you may have problems swallowing (dysphagia), which in turn may cause weight loss and malnutrition.
• Aspiration and pneumonia. Difficulty swallowing may also lead to entrance of food or liquids, including saliva, into your lungs (aspiration), which can lead to pneumonia.
• Breathing problems. If your chest muscles are affected by the disease, you may experience breathing problems, such as shortness of breath or in severe cases, respiratory failure.
• Calcium deposits. Late in the disease, particularly if you've had the disease for a long time, deposits of calcium can occur in your muscles, skin and connective tissues (calcinosis).

Associated conditions
Although these are not complications, polymyositis is often associated with other conditions that may cause further complications of their own, or in combination with polymyositis symptoms. Associated conditions include:

• Raynaud's phenomenon. This is a condition in which your fingers, toes, cheeks, nose and ears turn pale when exposed to cold temperatures.
• Other connective tissue diseases. Other conditions, such as lupus, rheumatoid arthritis, scleroderma and Sjogren's syndrome, can occur in combination with polymyositis.
• Cardiovascular disease. Polymyositis may cause the muscle of your heart to become inflamed (myocarditis). In a small number of people who have polymyositis, congestive heart failure and heart arrhythmias may develop.
• Lung disease. A condition called interstitial lung disease may occur with polymyositis. Interstitial lung disease refers to a group of disorders that cause scarring (fibrosis) of lung tissue, making lungs stiff and inelastic. Signs and symptoms include a dry cough and shortness of breath.

Tests and diagnosis

Diagnosis of polymyositis isn't always easy and can be a lengthy process. Even though the attempt to diagnose your condition may be frustrating, remember that an accurate diagnosis is necessary to receive appropriate treatment.

In addition to a thorough physical exam, your doctor will likely use other tests to confirm a diagnosis of polymyositis.

Imaging tests

• Magnetic resonance imaging (MRI). A scanner creates cross-sectional images of your muscles from data generated by a powerful magnetic field and radio waves.

  As MRI has become more sensitive, doctors have been using it more to diagnose inflammatory myopathies. MRI can detect active inflammation in your muscles, fibrosis and calcification. Its high sensitivity can detect subtle muscle inflammation and swelling early in the disease. A benefit of MRI is that it can look at large amounts of muscle to look for patterns or patches of muscle weakness, instead of taking a small sample from a single muscle, for example.

Muscle tests

• Electromyography. A doctor with specialized training inserts a thin needle electrode through the skin into the muscle to be tested. Electrical activity is measured as you relax or tighten the muscle, and changes in the pattern of electrical activity can confirm a muscle disease. The doctor can determine the distribution of the disease by testing different muscles.
• Muscle biopsy. A small piece of muscle tissue is removed surgically for laboratory analysis. A muscle biopsy may reveal abnormalities in your muscles, such as inflammation, damage or infection. The tissue sample can also be examined for the presence of abnormal proteins and checked for enzyme deficiencies. In polymyositis, a muscle biopsy typically shows inflammation, dead muscle cells (necrosis), and degeneration and regeneration of muscle fibers.

Blood tests

• Blood analysis. A blood test will let your doctor know if you have elevated levels of muscle enzymes, such as creatine kinase (CK) and aldolase. Increased CK and aldolase levels can indicate muscle damage. A blood test can also detect specific autoantibodies associated with different symptoms of polymyositis, which can help in determining the best medication and treatment.

Treatments and drugs

Although there's no cure for polymyositis, treatment can improve your muscle strength and function. The earlier treatment is started in the course of polymyositis, the more effective it is, leading to fewer complications.

Drugs

• Corticosteroids. These medications suppress your immune system, limiting the production of antibodies and reducing muscle inflammation, as well as improving muscle strength and function. Corticosteroids, especially prednisone, are usually the first choice in treating inflammatory myopathies such as polymyositis.

  Your doctor may start with a very high dose, and then decrease it as your signs and symptoms improve. Improvement generally takes about two to four weeks, but therapy is often needed for years.

  Prolonged use of corticosteroids can have serious and wide-ranging side effects, so your doctor may recommend supplements to combat them, such as calcium and vitamin D, and may prescribe bisphosphonates, such as alendronate (Fosamax), risedronate (Actonel) or zoledronic acid (Reclast). Bisphosphonates in pill form may not be recommended if you have difficulty swallowing.

• Corticosteroid-sparing agents. Your doctor may recommend other medications, either to decrease side effects or if your condition doesn't respond to corticosteroids. These medications include azathioprine (Imuran) or methotrexate (Rheumatrex). Your doctor may prescribe these alone or in combination with corticosteroids.

  When in combination, these additional immunosuppressants can be used to lessen the dose and potential side effects of the corticosteroid. Immunosuppressants, such as cyclophosphamide (Cytoxan) and cyclosporine (Neoral, Sandimmune), may improve signs and symptoms of polymyositis and interstitial lung disease.

Antibody therapy

• Intravenous immunoglobulin (IVIg). Immunoglobulin contains healthy antibodies from blood donors. High doses can block the damaging antibodies that attack muscle in polymyositis.

Immunosuppressive therapies
In addition to corticosteroids and immunosuppressive drugs, other treatments to suppress your immune system include:

• Tacrolimus (Prograf). This transplant-rejection drug may work to inhibit the immune system. Tacrolimus is often used topically to treat dermatomyositis and other skin problems. When taken orally, it may be helpful in treating people who have polymyositis complicated by interstitial lung disease.

Investigational treatment

• Biological therapies. Rituximab (Rituxan) has been studied in small numbers of people with polymyositis and dermatomyositis and shown to improve muscle strength, lung involvement and skin rash. Tumor necrosis factor (TNF) inhibitors such as etanercept (Enbrel) and infliximab (Remicade) have not been shown to be effective in trials with small numbers of people with polymyositis or dermatomyositis. Rituximab is not approved by the Food and Drug Administration for the treatment of polymyositis, so your insurance company will likely require preapproval if you wish to be reimbursed.

Other treatment

• Physical therapy. A physical therapist can show you exercises to maintain and improve your strength and flexibility and advise an appropriate level of activity.
• Dietetic assessment. Later in polymyositis, chewing and swallowing can become more difficult. A registered dietitian can teach you how to prepare easy-to-eat foods.
• Speech therapy. If your swallowing muscles are weakened by polymyositis, speech therapy can help you learn how to compensate for those changes.

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