Cutaneous sinus histiocytosis (Rosai-Dorfman disease) presenting clinically as vasculitis.

The cutaneous variant of Rosai-Dorfman disease is a rare benign lymphoproliferative disorder that occurs without lymphadenopathy or internal organ involvement. We present a 55-year-old woman with a diffuse exanthematous eruption that evolved into pruritic papulopetechial and purpuric lesions on the back and lower extremities, diagnosed clinically as a vasculitis. The patient's lesions cleared spontaneously with no recurrence. Histopathologic examination showed a dense dermal nodular lymphohistiocytic infiltrate with occasional eosinophils, plasma cells, and neutrophils and with numerous extravasated red blood cells. The large, foamy histiocytes exhibited abundant pale cytoplasm, feathery cytoplasmic borders, and emperipolesis. A few histiocytes had longitudinal nuclear grooves resembling Langerhans cells; however, these cells were positive for S-100 protein and negative for CD1a. The clinical presentation of the cutaneous variant of Rosai-Dorfman disease is generally nonspecific. We present this case because of the unusual clinical presentation mimicking a vasculitis.