18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in the Assessment of Occult Involvement in Widespread Granulomatosis with Polyangiitis (Wegener's Granulomatosis).

Granulomatosis with polyangiitis (GPA) can be classified as classic triad of organ involvement consisting of lungs, upper respiratory tract/sinuses, and kidneys; limited which is not having the full triad; or widespread with additional organ involvement for example prostate, spleen, skin, eyes or peripheral nervous system and occasionally other organs. GPA is associated with increased 18F-fluorodeoxyglucose (FDG) uptake on positron emission tomography/computed tomography (PET/CT). PET/CT has the advantages of whole-body imaging and detecting metabolic abnormality before structural changes. FDG PET/CT is used to assess the extent of the disease in GPA and can detect site of occult disease involvement where there are metabolic evidence of defined organ involvement with no CT or clinical evidence. This may result in upgrading of the disease from limited to classic triad or from classic triad to widespread.