Dermatomyositis

Abstract

Abstract Dermatomyositis (DM) is an autoimmune disorder affecting the skin, skeletal muscle and, in some patients, the lungs. At one end of the spectrum myopathy predominates, at the other end skin disease is prominent with minimal or absent myositis (amyopathic DM). Most patients develop a facial rash initially; all sites can be affected but upper eyelid involvement is typical. A rash on the hands, extensor surfaces of the limbs, upper torso and scalp tends to occur subsequently. Muscle disease in DM usually becomes clinically apparent in the weeks to months after the onset of skin signs. DM can be a paraneoplastic disorder with up to 30% of patients having an internal malignancy, therefore investigations must include screening for an underlying neoplasm. Myositis‐specific antibodies (MSAs) target a variety of cell function proteins, some of which may be pathogenic. Currently MSAs are used to stratify DM patients into subgroups characterised by shared clinical traits. Systemic corticosteroid is the primary treatment for DM when both skin and muscles are involved. Immunosuppressant drugs (such as mycophenolate mofetil, azathioprine and tacrolimus) are used to control the disease as the dose of prednisolone is tapered. Intravenous immunoglobulin can be used as a steroid‐sparing agent; it is effective for both muscle and skin features in DM. Topical therapy for skin DM, including super‐potent steroids, is often disappointing; however recent studies have suggested the efficacy of Janus kinase inhibitors for DM skin disease.