Dermatomyositis is an inflammatory myopathy that affects the skin and muscles. It is characterized by progressive proximal symmetrical muscle weakness, elevated muscle enzyme levels, abnormal electromyography and muscle biopsy findings. The cause is unknown but may involve genetic, immunological, infectious or environmental factors. Diagnosis involves assessing muscle symptoms, rashes and laboratory tests showing muscle inflammation. Treatment focuses on sun protection, immunosuppressants like hydroxychloroquine and methotrexate, and corticosteroids. Lifestyle measures like diet, activity and sun avoidance are also important.