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Autoimmune Myositis


Alana M. Nevares

, MD, The University of Vermont Medical Center

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  • Doctors check muscle enzymes in the blood and may test electrical activity of muscles, do magnetic resonance imaging on muscles, and examine a piece of muscle tissue.

  • Corticosteroids, immunosuppressive drugs, immune globulin, or a combination is usually helpful.

These disorders result in muscle inflammation (myositis), disabling muscle weakness, and occasionally tenderness. The weakness typically occurs in the shoulders and hips but can affect muscles symmetrically throughout the body.

The cause of autoimmune myositis is unknown. Viruses may play a role, and cancer may occasionally trigger this disorder. The disorder can run in families.

There are four types of autoimmune myositis:

  • Polymyositis

  • Dermatomyositis

  • Necrotizing immune-mediated myopathies

  • Inclusion body myositis

Dermatomyositis usually causes skin changes that do not occur in polymyositis, which helps doctors differentiate the two disorders. Biopsy samples of muscle also look different under the microscope.

Necrotizing immune-mediated myopathies are disorders that kill muscle cells (myocytes) and do not damage tissue other than the muscles.

Inclusion body myositis is a separate disorder that has symptoms similar to chronic polymyositis of unknown cause. However, this disorder develops in older people, frequently involves other muscles (for example, hand and foot muscles) often with muscle wasting, progresses slower, and does not respond to therapy. Also, the muscle tissue has a different appearance under the microscope.

Symptoms of Autoimmune Myositis

The symptoms of autoimmune myositis are similar for people of all ages, but the muscle inflammation often appears to develop more abruptly in children than in adults. Symptoms, which may begin during or just after an infection, include symmetrical muscle weakness (particularly in the upper arms, hips, and thighs), joint pain (but often little muscle pain), difficulty in swallowing Difficulty Swallowing Some people have difficulty swallowing (dysphagia). In dysphagia, foods and/or liquids do not move normally from the throat (pharynx) to the stomach. People feel as though food or liquids become... read more , fever, fatigue, and weight loss. Raynaud phenomenon Raynaud Syndrome Raynaud syndrome, a functional peripheral arterial disease, is a condition in which small arteries (arterioles), usually in the fingers or toes, narrow (constrict) more tightly than normal in... read more Raynaud Syndrome (in which the fingers suddenly become very pale and tingle or become numb in response to cold or emotional upset) may also occur.

Muscle weakness may start slowly or suddenly and may worsen for weeks or months. Because muscles close to the center of the body are affected most, tasks such as lifting the arms above the shoulders, climbing stairs, and getting out of a chair or off of a toilet seat can become very difficult. If the neck muscles are affected, even raising the head from a pillow may be impossible. People who have weakness in the shoulders or hips may need to use a wheelchair or may become bedridden. Muscle damage in the upper part of the esophagus can cause swallowing difficulties and regurgitation of food. The muscles of the hands, feet, and face, however, are not usually affected.

Joint aches and inflammation occur in about 30% of people.

Skin changes occur in people who have dermatomyositis. Rashes tend to appear at the same time as muscle weakness and other symptoms. A dusky or purplish rash (called a heliotrope rash) can appear on the face with reddish purple swelling around the eyes. The rash may also be raised and scaly and may appear almost anywhere on the body but is especially common on the knuckles, elbows, knees, outer part of upper thighs, and parts of the hands and feet. The area around the nails may redden or thicken. When the rash fades, brownish pigmentation, scarring, shriveling, or pale depigmented patches may develop on the skin. The rash on the scalp may look like psoriasis and be intensely itchy. Sun sensitivity and sores on the skin occur as well. Bumps composed of calcium may develop under the skin or in muscle, particularly in children. Raised, reddish bumps may appear on the large knuckles (called Gottron papules) and sometimes on the small knuckles.

Sometimes these characteristic skin changes occur in people who do not have muscle weakness and inflammation. In this case, the disorder is called amyopathic dermatomyositis.

Diagnosis of Autoimmune Myositis

  • Established criteria

  • Muscle biopsy

Doctors use the following criteria to make the diagnosis of autoimmune myositis:

Muscle biopsy is often done and is the most conclusive way to diagnose autoimmune myositis, especially when the diagnosis is not clear. Muscle biopsy is not usually necessary when people have characteristic skin changes of dermatomyositis.

Other laboratory tests cannot specifically identify autoimmune myositis, but they can help doctors rule out other disorders, detect the risk of complications, and determine severity. Blood tests are done to detect levels of antinuclear antibodies (ANA) and other antibodies, which are present in most people who have autoimmune myositis. Although blood test results can help doctors diagnose autoimmune myositis, they alone cannot confirm a definite diagnosis of autoimmune myositis because sometimes the abnormalities they detect are present in healthy people or in people who have other disorders. The diagnosis of autoimmune myositis is based on all of the information doctors gather, including symptoms, physical examination results, and all test results.

MRI may also help the doctor select a site for biopsy. Special tests done on muscle tissue samples may be needed to rule out other muscle disorders.

Doctors often suggest cancer screening for people age 40 or older who have dermatomyositis or for people age 60 or older who have polymyositis because these people may have unsuspected cancers.

Prognosis of Autoimmune Myositis

Up to 50% of people (especially children) who have received treatment within 5 years of diagnosis often have a long symptom-free period (remission), and some may even appear to recover completely. However, the disorder may still return (relapse) at any time. About 75% of people survive at least 5 years after the diagnosis is made. This percentage is even higher among children.

Children who have the juvenile form of dermatomyositis may develop severe inflammation of the blood vessels (vasculitis Overview of Vasculitis Vasculitic disorders are caused by inflammation of the blood vessels (vasculitis). Vasculitis can be triggered by certain infections or drugs or can occur for unknown reasons. People may have... read more Overview of Vasculitis ) that supply the bowel, which can ultimately lead to bowel perforation if untreated.

Polymyositis tends to be more severe and resistant to treatment in people whose heart or lungs are affected. Polymyositis and particularly dermatomyositis have been linked to an increased risk of cancer. In people who have cancer, it is the cancer rather than the autoimmune myositis that is the cause of death.

Treatment of Autoimmune Myositis

  • Corticosteroids

  • Immunosuppressive drugs

  • Sometimes immune globulin

Modest restriction of activities when the muscle inflammation is most intense often helps.

Generally, the corticosteroid prednisone is given by mouth in high doses. This drug slowly improves strength and relieves pain and swelling, controlling the disease. People who have severe disease with swallowing difficulty or weakness of the muscles needed for breathing are given a corticosteroid such as methylprednisolone by vein. Many adults must continue taking prednisone (at the lowest effective dose) for months.

To monitor how the disorder is responding to corticosteroid treatment, doctors periodically do a blood test to measure the levels of muscle enzymes. The levels usually fall to normal or near normal and muscle strength returns after about 6 to 12 weeks. MRI may also show areas of inflammation and help the doctor determine how the disorder is responding to treatment. Once enzyme levels have returned to normal, prednisone can be gradually reduced. If muscle enzyme levels rise, the dose is increased.

Although doctors typically give corticosteroids first when treating people who have autoimmune myositis, these drugs do cause side effects (for example, high blood sugar, mood swings, cataracts, risk of fractures, and glaucoma), especially if they are given at high doses for a long time. Therefore, to minimize long-term corticosteroid use and the side effects, an immunosuppressive drug (such as methotrexate, tacrolimus, azathioprine, mycophenolate mofetil, rituximab, or cyclosporine) may be used in addition to prednisone. Another possible treatment is immune globulin (a substance that contains large quantities of many antibodies) given by vein (intravenously). Some people receive a combination of corticosteroids, immunosuppressive drugs, and immune globulin.

When muscle weakness is associated with cancer, it usually does not respond well to prednisone. However, the muscle weakness usually lessens in severity if the cancer can be successfully treated.

People who have autoimmune myositis are at increased risk of atherosclerosis Atherosclerosis read more and are closely monitored by doctors.

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