Myositis, also referred to as inflammatory myopathy, means inflammation of the muscles. There are different causes, however injuries, infections, or autoimmune diseases are central.
Viral infections are the most common infections causing myositis. Rarely, bacteria, fungi, or other organisms can cause myositis as well. Viruses or bacteria may invade muscle tissue directly, or release substances that damage muscle fibers. Common cold and flu viruses, as well as HIV, are just a few of the viruses that can cause myositis. Drugs causing myositis or myopathy include: statins; colchicine; plaquenil (hydroxychloroquine); alpha-interferon; cocaine; alcohol. Injury: Vigorous exercise can lead to muscle pain, swelling, and weakness for hours or days after a workout. Inflammation contributes to these symptoms, technically making this a form of myositis. Myositis symptoms after exercise or injury nearly always resolve completely with rest and recovery.
Polymyositis, dermatomyositis, and juvenile myositis are all autoimmune diseases, meaning the body’s immune system is attacking the muscle. While the immune system may also cause muscle damage in inclusion body myositis, this may not be cause of this disease. Although myositis is often treatable, these diseases are poorly understood and do not always completely respond to current medications.
In the United States, there are an estimated 1,600 to 3,200 new cases per year and 50,000 to 75,000 people living with myositis.
Myositis can affect both children and adults. With the exception of one type of myositis, women are more likely to be affected by this disease than men.