The term “myositis” refers to a general inflammation or swelling of the muscle. Many people have experienced sore muscles after vigorous exercise, a condition that is temporary and improves with rest. Other conditions that can cause muscle weakness and pain include infection, muscle injury from medications, inherited diseases, electrolyte imbalances, and thyroid disease.

More often, however, the term myositis is used to refer to a disease involving chronic inflammation of the muscles, often occurring together with other symptoms. This condition is also known as idiopathic inflammatory myopathy (IIM). The disease is highly variable and has been classified into a number of forms, including dermatomyositis (DM), polymyositis (PM), necrotizing myopathy (NM), sporadic inclusion body myositis (sIBM), and juvenile forms of myositis (JM).

Inflammatory Myopathies

Inflammatory myopathies are autoimmune diseases, meaning the body’s immune system, which normally fights infections and viruses, is misdirected and begins to attack the body’s own normal, healthy tissue. Inflammatory myopathies are rare diseases. All forms combined affect an estimated 50,000 to 75,000 people in the United States. While it is still unclear what causes myositis, some scientists believe certain individuals have a genetic predisposition to develop an autoimmune disease, which is triggered by an environmental exposure to some trigger, such as infection, virus, toxin, or sunlight.


Symptoms of weakness, swelling, and muscle damage often appear gradually. Long before patients are diagnosed, they may have trouble getting up from a chair, climbing stairs, or grasping objects with their hands. Patients may fall, find it difficult to reach their arms up, have difficulty swallowing, or other symptoms.


Myositis is often difficult to diagnose, because many physicians are unfamiliar with the disease and its symptoms. It is a rare disease, so it is also difficult to conduct adequate research to test new treatments, so there is a lot of confusion among the medical community over how to effectively manage patients with myositis. Nevertheless, myositis is a serious illness that, in most cases, needs to be treated aggressively. With inadequate or no treatment, myositis can cause significant disability and even death. There is no cure for any of the forms of myositis.