Myositis- Polymyositis, Dermatomyositis

Myositis is a muscle disease when the immune system damages the muscles and make them weak. Weakness is usually in the large muscles around the neck, shoulders and hips. There is trouble climbing stairs, getting up from a seat, or reaching for overhead objects. There is usually very little pain in the muscles. Severe disease can cause choking while eating, shortness of breath and breathing food into the lungs.

Polymyositis and Dermatomyositis have muscle inflammation and weakness, while patients with Dermatomyositis also have a rash. The rash is usually purple or red spots on the upper eyelids or upper chest which is worse with sun exposure, and they can also have scaly red bumps on the knuckles, elbows or knees. Amyopathic dermatomyositis has only the skin involvement. There can also be inflammation in the lungs with cough and shortness of breath or in the blood vessels which can cause skin damage.

Myositis is rare, about 1 person in 100,000 and can occur at any age, but often between ages 5 – 10 and 40 – 50, and women are affected twice as often as men. To determine the cause of weakness, blood tests for evidence of muscle damage and immune system tests are done, and then an electromyogram, muscle biopsy or MRI scan can establish the diagnosis.

Treatment is started with oral corticosteroids and blood tests should improve in 4-6 weeks while muscle strength should return in 2-3 months. To help lower the dose of corticosteroids, Methotrexate, Imuran, IVIg, Neoral, Prograf, Cellcept and Rituxan can be used. Physical therapy to improve range of motion and strength is important for preventing contractures of joints and maintaining function.

Dermatomyositis more than Polymyositis may be related to an underlying cancer which should prompt appropriate testing. The Myositis Association is available for more information.