Inflammatory myopathies are a group of muscle disease where the muscle is attacked by the body’s own immune system. Types of myositis include:
- Polymyositis – inflammation of several muscles at once
- Dermatomyositis – polymyositis accompanied by involvement of the skin
- Inclusion body myositis
The cause of myositis is unclear, but involves a misdirected immune response. The onset of myositis can vary from childhood (as in dermatomyositis) to late adult life (as in inclusion body myositis). Progression is gradual with increasing weakness if untreated.
Symptoms of myositis include weakness of the hips, thighs, upper arms and shoulders. In inclusion body myositis, the forearms become weak making tasks involving the hands difficult. In dermatomyositis, a distinctive purplish rash is often seen on the backs of the hands or across the face and painful nodules can be felt under the skin. Swallowing difficulties also frequently occurs in myositis.
The diagnosis of myositis is based on the clinical appearance, electrophysiology (EMG) and blood work as well as examination of muscle tissue from biopsy. The muscle biopsy is crucial in solidifying the diagnosis. In inflammatory myopathies, healthy muscle fibers will be surrounded and invaded by inflammatory cells, a feature called “primary inflammation.”
Once a diagnosis of myositis has been made, treatment involves controlling the immune system so that muscle is no longer inappropriately attacked. The mainstay of treatment is corticosteroids. However, multiple immunomodulatory agents are available to use in conjunction with corticosteroids to reduce the amount and length of time that steroids are necessary. This decreases the side effects from treatment. Immunomodulatory agents used in the treatment of myositis include methotrexate, azathioprine, mycophenolate mofetil and intravenous immunoglobulin, among others.
At Johns Hopkins, myositis is treated by a team of health care professionals that include neurologists specifically trained in muscle disease, physiotherapists to recommend a specific rehabilitation plan and Muscular Dystrophy Association liaisons to provide a variety of financial, social and equipment needs.