18F-Fluorodeoxyglucose PET in Rheumatologic and Autoimmune Disorders.

FDG PET detects the silent inflammation of autoimmune and rheumatologic diseases even before tissue damage, as activated leukocytes overexpress glucose transporters. It has an important role in large vessel vasculitis which includes early diagnosis, disease monitoring and response assessment to treatment. In inflammatory arthritides, it quantifies synovitis and enthesitis and detects early treatment response. In connective tissue and immunoglobulin G4 related diseases, whole body imaging maps silent disease, helps exclude malignancy, and guides biopsy. It is central to cardiac sarcoidosis and an early test in fever of unknown origin.