Diffuse increased kidney FDG uptake in a patient with fever of unknown origin-guided biopsy and assisted the diagnosis of microscopic Polyangiitis

Fluorodeoxyglucose F¹⁸ positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) plays a pivotal role in investigating cases of fever of unknown origin (FUO), facilitating precise diagnoses and enabling effective treatments. Inflammatory changes without abnormal immunoglobulin deposits. Chest X-rays, echocardiography, magnetic resonance imaging of the entire spine, and CT angiography could not identify the cause of the fever. In this case, the ¹⁸F-FDG PET/CT could identify abnormalities that could not be detected by conventional imaging, leading to the kidney biopsy that was the crucial to establish the final diagnosis and appropriate treatment. Therefore, our report highlights the roles of ¹⁸F-FDG PET/CT in the evaluation of FUO.