RESUMEN
Evaluation of a fever of unknown origin (FUO) is complex. Recently, PET scanning has been approved for screening in FUO evaluation. We treated three cases of FUO associated with increased FDG uptake in the bone marrow of the femur and tibia on the fusion PET/CT; all three had the same pattern of uptake. Bone marrow biopsies revealed mature lymphocyte and histiocyte infiltration and myxoid changes in one case, and cortical bone involvement in another case. The cases were all young females who had fever with neutropenia and relative lymphocytosis that lasted for several weeks and then remitted spontaneously. Even though the results of the studies were not diagnostic, the unique uptake pattern on PET/CT and the histology might be related to the cause of the illness and should be studied further to assess the association with classic FUO.