Abstract

Dermatomyositis is an immune-mediated myositis with characteristic clinical skin findings, including violaceous papules and plaques on the scalp, eyelids, central face, elbows, knees, and dorsal hands.  Rarely, dermatomyositis can present as panniculitis. Dermatomyositis-associated panniculitis most frequently involves the upper and lower extremities and presents as painful subcutaneous nodules or plaques.  In previously reported cases, the histopathology of dermatomyositis panniculitis typically shows non-specific lobular panniculitis with the inflammatory infiltrate composed of lymphocytes and plasma cells, often with rimming of necrotic adipocytes.  Long-standing lesions show hyaline necrosis of the entire fat lobule, often with calcification. Abundant mucin is typically seen both in the dermis and in the connective tissue of the septa within the subcutis. We report a case of a 79-year-old woman with a three-year history of amyopathic dermatomyositis with typical skin manifestations who developed multiple tender, subcutaneous nodules in the left upper extremity. Histopathology of the nodules demonstrated septal fibrosis with fat necrosis of intervening lobules with focal acute inflammation in the fibrotic septa. Abundant mucin deposition was seen both within the fibrous septa of the subcutis and between collagen bundles of the dermis. No calcifications were identified. In the context of the patient’s history of dermatomyositis and the abundant mucin seen in the dermis and involving the fibrous septa of the subcutis, the findings were favored to represent long-standing panniculitis in the setting of dermatomyositis. Panniculitis is a rare presentation of dermatomyositis and the histopathology of the panniculitis as fat necrosis in this case has not been reported previously.