Dermatomyositis

Dermatomyositis is a systemic autoimmune disease characterized by inflammation of skin and skeletal muscles, with characteristic immune patterns including antibodies to myositis-associated antigens. The pathophysiology involves antibody-mediated complement activation leading to destruction of muscle and skin vasculature, with prominent CD4+ T cell infiltration. Muscle involvement typically affects proximal muscles (shoulders, hips) more than distal muscles, causing progressive weakness that can be profoundly disabling. Skin manifestations are characteristic: heliotrope rash (purple/violet discoloration of eyelids), Gottron papules (flat-topped papules over knuckles), and photosensitive rashes affecting shoulders, chest, and neckline. Calcinosis cutis (calcium deposits in skin) develops particularly in juvenile-onset disease. Systemic manifestations include constitutional symptoms, malaise, and potential pulmonary involvement (interstitial lung disease in up to 30% of patients) and esophageal involvement causing dysphagia. Up to 30% of adult patients have underlying occult malignancy at diagnosis or develop malignancy subsequently. Myositis-specific antibodies (including anti-Jo-1, anti-Mi-2, anti-CADM-140) are present in about 60% of patients and have prognostic significance.