<s>[INST] <<SYS>> This is a medical question of type : causes <</SYS>> What causes Dermatomyositis ? [/INST] What causes dermatomyositis? The cause of this disorder is unknown. It is theorized that an autoimmune reaction (reactions caused by an immune response against the body's own tissues) or a viral infection of the skeletal muscle may cause the disease. In addition, some doctors think certain people may have a genetic susceptibility to the disease. </s>