Dermatomyositis is a rare autoimmune disease that can cause muscle weakness and a skin rash. This condition is twice as common in women than in men, and onset is typically at 50-70 years of age. For many people, the rash develops before muscle weakness will develop, and the first symptoms are often itching and burning. In some people, muscle weakness develops without any rash. Muscle weakness in dermatomyositis typically affects the muscles closest to the trunk (upper arms and thighs), which causes difficulty in climbing stairs, standing from a squat, lifting objects, raising arms above the head, and swallowing. In some people, the rash may develop without ever having any muscle weakness. The following are specific types of rash associated with dermatomyositis:
- Red or purple patches in sun-exposed areas
- A purple rash on the cheeks, nose, shoulders, upper chest, and elbows
- Purple eyelids, described as the “heliotrope rash” of dermatomyositis
- Purple bumps on the back of knuckles, called Gottron papules
- Ragged cuticles and large blood vessels near the cuticles
- Thinning of hair on the scalp associated with scaling
There are several tests that can be performed to help confirm the diagnosis of dermatomyositis. Blood tests to detect increased levels of circulating muscle enzymes are used to detect muscle injury. Blood tests to detect autoantibodies can be used to help make the diagnosis of dermatomyositis or determine specific disease associations, such as associated lung disease. Skin biopsy can be very helpful in determining if the rash is from dermatomyositis, and muscle biopsy can determine if there is myopathy related to the disease. Two other ways to assess the muscles without biopsy include electromyography testing or MRI scan. Your dermatologist may perform skin biopsy or blood work to help assess for dermatomyositis and will help treat the skin condition associated with the disease. Referral to a rheumatologist would be helpful, especially if there is muscle involvement.
Treatment often includes an oral corticosteroid, especially early in the disease or during a flare up. Immunosuppressive or cytotoxic medications may also be used, including methotrexate, azathioprine, mycophenolate mofetil, cyclosporine, or cyclophosphamide. Antibody-based medications may occasionally be used, including intravenous immunoglobulin (IVIG) or the biologic medication rituximab. Other medications may include hydroxychloroquine and colchicine. Importantly, the rash of dermatomyositis is very sun sensitive, so sunscreen, avoidance of direct sunlight, and sun protective clothing are very important.
Most people who have dermatomyositis will require treatment throughout the rest of life. The disease can completely resolve in about 20% of people affected. People may also die from associated heart or lung disease or from an underlying cancer.