Modest restriction of activities often helps when muscle inflammation is most intense.
Generally, the corticosteroid prednisone (a type of immunosuppressant) is given by mouth in high doses. This medication slowly improves strength and relieves pain and swelling, controlling the disease. Many adults must continue taking prednisone (at the lowest effective dose) for months. 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.
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 during treatment and muscle strength returns after approximately 6 to 12 weeks. MRI may also show areas of inflammation and help doctors determine whether treatment is working. Once enzyme levels have returned to normal, prednisone can be gradually reduced. If muscle enzyme levels rise again, the dose is increased.
Although doctors typically give corticosteroids first when treating people who have idiopathic inflammatory myopathy, these medications 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, another immunosuppressant (such as methotrexate, tacrolimus, azathioprine, mycophenolate mofetil, or rituximab) may be given 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, immunosuppressants, and immune globulin.
When the idiopathic inflammatory myopathy is related to a cancer, it is usually more difficult to treat with immunosuppressants. However, if the cancer is successfully treated, the myopathy becomes easier to treat.
People who take corticosteroids are at risk of fractures related to osteoporosis. To prevent osteoporosis, these people are given supplements of vitamin D and calcium, and sometimes medications to treat osteoporosis.
People who are receiving immunosuppressants are also given medications to prevent infections such as by the fungus Pneumocystis jirovecii (see prevention of pneumonia in people with a weakened immune system) and vaccines against common infections such as pneumonia, influenza, and COVID-19.
People who have idiopathic inflammatory myopathy are at increased risk of atherosclerosis and are closely monitored by doctors.
