Diffuse renal (18)F-FDG uptake of a patient with fever of unknown origin revealed sarcoidosis.

We report about the usefulness of F-FDG PET for the detection and therapy response evaluation of renal sarcoidosis. A 55-year-old woman presented with a condition diagnosed with pulmonary and ocular sarcoidosis 2 years before having anemia and acute deterioration of renal function. FDG PET revealed diffuse increased FDG uptake in both kidneys and the spleen. Histopathologic examination of a renal biopsy sample revealed granulomatous interstitial nephritis with sarcoidosis. After methylprednisolone treatment, the abnormal FDG uptake resolved completely with improvement of symptoms. FDG PET is a useful tool to detect active sarcoidosis regions and to monitor treatment efficacy.