RESUMO
Sinus histiocytosis with massive lymphadenopathy, also known as Rosai-Dorfman disease is a rare disorder characterized by proliferation of distinctive histiocytes within lymph node sinuses and lymphatics, sometimes involving extranodal sites. However, clinical suspicion is difficult and there is also a lack of useful diagnostic markers for this disorder prior to histological confirmation. High elevation of serum ferritin is known to be a useful diagnostic marker for various hematologic diseases, including hemophagocytic lymphohistiocytosis and lymphoma. Here, we report a case of fever of unknown origin that presented along with highly elevated serum ferritin (5,780 ng/mL), and was finally diagnosed as Rosai-Dorfman disease by lymph node biopsy.