Inflammatory Myopathies

Overview

The myopathies are neuromuscular disorders in which the primary symptom is muscle weakness due to dysfunction of muscle fiber. Other symptoms of myopathy can include include muscle cramps, stiffness, and spasm. Myopathies can be inherited (such as the muscular dystrophies) or acquired (such as common muscle cramps). Myopathies are grouped as follows:
congenital myopathies: characterized by developmental delays in motor skills; skeletal and facial abnormalities are occasionally evident at birth

Inflammatory Myopathies

The inflammatory myopathies are a group of muscle diseases that involve inflammation of the muscles or associated tissues, such as the blood vessels that supply the muscles. A myopathy is a muscle disease, and inflammation is a response to cell damage. The inflammatory process leads to destruction of muscle tissue, and is accompanied by weakness and sometimes pain. Over time, there can be loss of muscle bulk (atrophy).

The four main types of chronic, or long-term, inflammatory myopathies are:

Causes

Myositis, or general muscle inflammation, may be caused by:

Although the cause of many inflammatory myopathies is unknown, the majority are considered to be autoimmune disorders, in which the body’s immune response system that normally defends against infection and disease attacks its own muscle fibers, blood vessels, connective tissue, organs, or joints.

Inflammatory myopathies aren’t genetic disorders, although there may be genetic factors that make it more or less likely that an inflammatory myopathy will develop.

Signs and Symptoms

General symptoms of chronic inflammatory myopathy include slow but progressive muscle weakness. Inflammation damages the muscle fibers, which causes weakness, and may affect the arteries and blood vessels that pass through muscle. Other symptoms include fatigue after walking or standing, frequent episodes of tripping or falling, and difficulty swallowing or breathing. Some individuals may have muscle pain or muscles that are tender to touch.

Falling and tripping are usually the first noticeable symptoms. The disorder often begins with weakness in the wrists and fingers that causes difficulty with pinching, buttoning, and gripping objects. People may experience weakness in their wrist and finger muscles and atrophy (thinning or loss of muscle bulk) in their forearm muscles and quadriceps muscles in the thighs. Difficulty swallowing occurs in approximately half of IBM cases due to involvement of the throat muscles.

Symptoms of the disease usually begin after the age of 50, although the disease can occur earlier. Unlike polymyositis and dermatomyositis, IBM occurs more frequently in men than in women.

Diagnosis

Diagnosis is based on medical history, results of a physical examination that includes tests of muscle strength, and blood samples that show elevated levels of various muscle enzymes and autoantibodies. Diagnostic tools include:

A biopsy sample of muscle tissue should be examined for signs of chronic inflammation, muscle fiber death, vascular deformities, or other changes specific to the diagnosis of a particular type of inflammatory myopathy. A skin biopsy can show changes in the skin associated with dermatomyositis.

Treatment

Chronic inflammatory myopathies cannot be cured in most adults but many of the symptoms can be treated. Options include:

Dermatomyositis, polymyositis, and necrotizing autoimmune myopathy are first treated with high doses of corticosteroid drugs, such as prednisone. This is most often given as an oral medication but can be delivered intravenously.

Immunosuppressant drugs, such as azathioprine and methotrexate, may reduce inflammation in individuals who do not respond well to prednisone. Periodic treatment using intravenous immunoglobulin can increase the chance for recovery in individuals with dermatomyositis, polymyositis, or NAM. Other immunosuppressive agents that may treat the inflammation associated with dermatomyositis and polymyositis include cyclosporine A, cyclophosphamide, mycophenolate mofetil, and tacrolimus.

Injections of adrenocorticotropic hormone gel may be another option for people who do not respond to or cannot tolerate other drug treatment options. Biologic therapies such as rituximab or tumor necrosis factor (TNF) inhibitors such as infliximab or etanercept may be used in severe cases where other treatment options have failed. However, there are very few studies that have shown how well these agents treat polymyositis and dermatomyositis.

Physical therapy is usually recommended to prevent muscle atrophy as well as to maintain muscle strength and range of motion. Bed rest for an extended period of time should be avoided, as people may develop muscle atrophy, decreased muscle function, and joint contractures. A low-sodium diet may help to reduce edema (swelling) and cardiovascular (heart and blood vessel) complications.  Occupational therapy can include an assessment of daily activities to address tasks such as feeding, bathing, and dressing.

Many individuals with dermatomyositis may need a topical ointment such as corticosteroids, tacrolimus, or pimecrolimus for their skin disorder. They should wear a high-protection sunscreen and protective clothing, particularly those who are light-sensitive. In rare instances, surgery may be required to remove calcium deposits that cause nerve pain and recurrent infections.

There is no standard, evidence-based course of treatment for inclusion body myositis. The disease is generally unresponsive to corticosteroids and immunosuppressive drugs. Some evidence suggests that immunosuppressive medications or intravenous immunoglobulin may have a slight, but short-lasting, beneficial effect in a small number of cases. Physical therapy may be helpful in maintaining mobility. Other therapy is symptomatic and supportive.

List of Medicines for PM & DM

Prognosis

In most cases, the symptoms of dermatomyositis resolve with therapy. The disease is usually more severe and resistant to therapy in individuals with heart problems. Approximately one-third of individuals with juvenile-onset dermatomyositis recover from their illness, one-third have a relapsing-remitting course of disease, and the other third have a more chronic course of illness.

The prognosis for polymyositis varies. Most individuals respond fairly well to therapy, but some people have a more severe disease that does not. These individuals may have significant disability. Since polymyositis can cause difficulty swallowing, people can become malnourished. They are also at increased risk for falling, which can lead to hip and other bone fractures, disability, or death. In rare cases people with severe and progressive muscle weakness can develop respiratory failure or pneumonia.

Although necrotizing autoimmune myopathy is more difficult to treat than polymyositis and dermatomyositis, it generally responds well to long-term combination immunosuppressive therapies.

IBM is generally resistant to all therapies and currently available treatments do little to slow its progression.

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