18F-FDG PET/CT Findings Overlapping Lymphoma in a Patient with Systemic Juvenile Idiopathic Arthritis.

Systemic juvenile idiopathic arthritis (sJIA) is an important autoinflammatory disease whose first symptom is usually fever, and life-threatening conditions such as macrophage activation syndrome can develop when diagnosis and treatment is delayed. sJIA is an exclusion diagnosis, and there is no specific test that distinguishes it from other febrile diseases. We report the positron emission tomography/computed tomography (PET/CT) findings of sJIA in a 12-year-old girl who presented with fever, rash, and arthralgia. ¹⁸F-fluorodeoxyglucose (FDG) uptake was observed in the spleen, bone marrow, and lymph nodes in ¹⁸F-FDG PET/CT performed to investigate the etiology of fever of unknown origin. The result of excisional biopsy performed with the suspicion of lymphoma from the left cervical lymph node with intense ¹⁸F-FDG uptake was reported as reactive hyperplasia. PET/CT is an alternative diagnostic method for patients with fever of unknown origin. In this case report, we emphasize that in patients with sJIA, there may be intense fluorodeoxyglucose-avid lymph nodes that may lead to the consideration of lymphoproliferative disease, and PET/CT findings along with spleen and bone marrow involvement may overlap with lymphoma.