Three cases of fever of unknown origin (FUO) with acute multifocal non-bacterial osteitis (NBO) as reactive osteomyelitis.

Evaluation for fever of unknown origin (FUO) requires a long list of studies. Recently, the validity of PET scan in FUO evaluation has been approved for screening and qualification. Non-bacterial osteitis (NBO) refers to non-bacterial and non-specific inflammation of bone, which is usually chronic, and involves multiple bony sites. We have experienced 3 cases of FUO associated with increased symmetric multiple fluorodeoxyglucose uptake preferentially at the epiphysis of the femur and tibia on fusion Positron emission tomography/Computed tomography (PET/CT). Patients were young women, who complained of intermittent fever lasting several months, which was associated only with neutropenia and relative lymphocytosis. Bone biopsies revealed increased lymphocytes and histiocyte infiltration of the cortical bone with reactive bone marrow. With no evidence of infection, the fever showed spontaneous remission within 2 weeks of conservative treatment. We report on 3 cases of FUO with self-limited acute NBO as reactive osteomyelitis and suggest that this unique pattern on PET/CT would be helpful for FUO evaluation.