Extranodal Rosai-Dorfman disease of the bone treated with surgery and radiotherapy

Rosai-Dorfman disease (RDD) is a rare, benign histiocyte disorder originally described by Rosai and Dorfman in 1969 as sinus histiocytosis with massive lymphadenopathy. It most typically presents as massive, painless cervical lymphadenopathy, and it is most often found in adolescents and young adults. Extranodal involvement is a common feature of RDD and may occur in more than 40% of patients. Less commonly, the disease can be seen in the bone. There are scattered case reports discussing the use of radiotherapy in the treatment of RDD. Here, we present a case of extranodal RDD of the femur in a 49-year-old African American female. The patient underwent three surgical procedures prior to undergoing radiotherapy. Pathology was consistent with extranodal RDD. The cells stained positive for CD68 and S-100. Pathognomonic features such as emperipolesis and replacement of the bone marrow by diffuse infiltrating of histiocytes and intervening bands of plasma cells proliferation were noted. Prior to radiotherapy, the patient required a walker to assist with ambulation and was utilizing a wheelchair while in the clinic. The decision was made to proceed with 30 Gy of external beam radiotherapy in 15 fractions. After five fractions, the patient's pain resolved entirely. She no longer required pain medication and was ambulating without assistance. She experienced no adverse events from the radiation. Extranodal RDD is a rare disorder, and evidence for treatment is derived from scattered case reports. Previous reports have indicated a dose response to radiotherapy in the 20-30 Gy range for RDD; however, our patient developed complete resolution of her symptoms after 10 Gy. While the optimal dose regimen has not yet been established, symptomatic patients appear to benefit from external beam radiotherapy for extranodal RDD.