Myositis is a rare disease that involves inflammation of the muscles. It can cause a variety of symptoms such as skin involvement (i.e., rashes), muscle weakness, and other organ involvement. Systemic symptoms such as weight loss, fatigue, and low fever can also present. Myositis is a type of myopathy, which is a general term that refers to diseases that affect the muscles that connect to your bones (skeletal muscles). Different forms of myositis affect different groups of muscles throughout your body.

Causes of myositis can include injury, medicines, infection, inherited muscle disease, or an autoimmune disorder. It can also be idiopathic (no known cause). Autoimmune disease is an abnormal immune response to a functioning body part, in this case, the muscles. The three main types of idiopathic myositis (known as inflammatory myopathies) that typically test positive for autoantibodies are dermatomyositis, polymyositis, and inclusion body myositis.

Diagnosis of myositis can involve a physical exam, lab tests, imaging tests, and a muscle biopsy. Blood tests can look for signs of damaged muscles, inflammation levels within the body, and the presence of autoantibodies, which are tiny proteins that can attack the body’s own healthy tissues and cells. There is no autoantibody test that can prove for certain that you have myositis, but there are tests that can be helpful in making a diagnosis.

Treatment options for myositis depend on the underlying cause. If myositis is caused by an autoimmune disease, glucocorticoids are often the first choice for treatment. This drug works to weaken the immune system so that the immune system is not able to attack the muscles. It is a type of steroid and can cause a wide array of side effects such as mood changes, increased hunger, trouble sleeping, etc. Another treatment option is a steroid-sparing immunosuppressive agent. Other treatment options can include medications, physical therapy, exercise, heat therapy, assistive devices, and rest.