Extra nodal Rosai Dorfman disease masquerading as metastatic soft tissue sarcoma- A case report.

Rosai Dorfman disease is rare benign disease of phagocytic histiocytosis usually present as painless massive lymphadenopathy. Extra nodal presentation of Rosai Dorfman disease is rare but also described. We hereby describe an unusual presentation of the extra nodal Rosai Dorfman disease with rapidly growing soft tissue lesion in the left thigh with associated osseous lesions in the right distal femur, left distal femur, left proximal tibia and presence of solitary pulmonary nodule. This case is unique as clinical presentation highly suspicious of soft tissue sarcoma but excision biopsy of thigh lesion showed Rosai Dorfman disease.Though RDD in extremities has been described in limited number of cases, to the best of our knowledge this is first case of lower extremity RDD associated with osseous lesions and pulmonary nodule but without lymphadenopathy.