An unusual co-occurrence of Langerhans cell histiocytosis and Rosai-Dorfman disease: report of a case and review of the literature.

BACKGROUND: The co-occurrence of Langerhans cell histiocytosis (LCH; disorder characterized by proliferation of Langerhans cells) and Rosai-Dorfman disease (RDD; histiocytic entity that is one of the non-Langerhans cell diseases) is extremely rare and raises several questions regarding the nature of the diseases. METHODS: We describe a 10-year-old boy who presented with a 3-month history of right scalp swelling. Clinical, pathological, and imaging evaluation disclosed multiple LCH of bone and cutaneous RDD. RESULTS: After initiating prednisone and vinblastine therapy, the patient developed an asymptomatic diffuse papular eruption. Biopsy revealed cutaneous RDD. Treatment was continued with a good response of bone LCH and significant amelioration of the cutaneous findings. CONCLUSIONS: Co-occurrence of LCH and RDD is a rare phenomenon. Various explanations, including the role of chemotherapy, are suggested based on our and several previously reported cases.