Erdheim-Chester disease: A rare cause of recurrent fever of unknown origin mimicking lymphoma

We report the case of a patient with recurrent fever of unknown origin (FUO) with prominent back pain, hepatosplenomegaly, and abdominal/pelvic adenopathy suggesting lymphoma. A bone biopsy showed histiocytic infiltration. Studies for lymphoma were negative, but immunohistochemical stains were diagnostic of Erdheim-Chester disease (ECD). ECD should be included as a rare cause of recurrent FUO with bone involvement.