Abstract<\/strong><\/p>\n

Introduction:<\/strong><\/span> Rosai-dorfman disease (RDD) or sinus histiocytosis with massive lymphadenopathy is a rare histiocytic proliferative disorder of unknown etiology first identified and characterized by Rosai and Dorfman in 1969. The disease is characterized by painless cervical lymphadenopathy, fever, leukocytosis, elevated erythrocyte sedimentation rate, and hypergammaglobulinemia. <500 patients have been reported worldwide. Osseous involvement without lymphadenopathy occurs in <10% of patients and is usually multifocal. Extranodal solitary osseous lesions are just 4% of this subpopulation, no more than 50 such cases have been described in the literature. Here, we report a rare case of RDD presenting as solitary lesion of the distal femur without any evidence of lymphadenopathy and normal laboratory work up.
\nCase Report:<\/strong> <\/span>We report the case of a 29-year-old female who presented with pain and swelling of distal femur of 2-month duration without any evidence of lymphadenopathy, with a normal laboratory workup. Radiographical evaluation showed an epiphyseal, osteolytic, and well-defined lesion with cortical break over the medial femoral condyle and soft-tissue extension into the medial patellar recess abutting the medial patellar retinaculum. Whole body positron emission tomography did not show any other sites of abnormal increased uptake. Intralesional extended curettage, bone grafting, bone cementing, and pinning were done. Histologically, the biopsied lesion demonstrated the classic histiocyte proliferation which exhibited emperipolesis (engulfment of lymphocyte or plasma cells by large histiocyte) which are CD-68, S-100 positive, and CD-1a negative on immunohistochemistry. At 2-year follow-up, the patient is symptom free, without any new osseous\/extranodal\/nodal lesions.
\nConclusion:<\/strong><\/span> RDD rarely affects bone as a primary or even secondary form of the disease. It has relatively non-specific radiological appearance causing diagnostic challenges and may lead to erroneous diagnosis of a malignancy. Biopsy and histological examination by an experienced pathologist is mandatory for the final diagnosis. The ideal treatment ranges from wait and see policy to surgery, chemotherapy, and radiotherapy.
\nKeywords:<\/strong><\/span> Rosai-Dorfman disease, Extranodal, Osseous, Histiocytosis, Emperipolesis<\/p>\n