Background AAVs are systemic autoimmune diseases which mainly involve small to medium sized vessels in a diversified and often unpredictable manner leading to disease patterns which can be difficult to diagnose upon first encounter. Moreover, early or clinically quiescent lesions may go unrecognized leading to missed therapeutic opportunities. While there is emerging evidence for a diagnostic role of FDG-PET/CT in large vessel vasculitis, there is still uncertainty concerning the utility of this technique in small vessel vasculitis.
Objectives To compare the number and distribution of inflammatory lesions in incident AAV as assessed by conventional diagnostics versus FDG-PET/CT.
Methods In 2009-2012, FDG-PET/CT was done in 17 patients who subsequently turned out to have AAV according to current criteria. Medical files were searched for vasculitis associated disease manifestations, laboratory/imaging findings and indications for FDG-PET/CT scans. The Birmingham Vasculitis Activity Score (BVAS) was calculated. All scans were re-evaluated visually and maximum standardized uptake values (SUVmax) were recorded.
Results Median age was 62 years (range 48-81), Female/Male ratio 5/12. Fourteen had granulomatosis with polyangiitis and 3 had eosinophilic granulomatosis with polyangiitis or microscopic polyangiitis. 6/17 had received intermediate or high dose glucocorticoid treatment for median 5 days (range 1-27) before scanning. Indications for FDG-PET/CT were suspected cancer 9/17 (53%), infection 3/17 (29%), vasculitis 2/17 (12%) and unspecified 1/17 (6%). A total of 15/17 (88%) had increased FDG uptake at one or more sites. The only 2 patients with a negative FDG-PET/CT scan had received glucocorticoids before the procedure.
The distribution of organ involvement assessed clinically or by FDG-PET/CT is presented in the table. Clinically silent sites with increased FDG uptake were recorded in 4 patients including the aorta, pericardium, lung and shoulder. Three additional patients had increased renal FDG uptake without corresponding laboratory findings indicating kidney disease. There was no correlation between SUV max and BVAS.
Conclusions A classical clinical approach was superior to FDG-PET/CT alone to detect small vessel vasculitis related disease manifestations in all organs. There was no correlation between SUV max and disease activity expressed as BVAS. Increased kidney FDG uptake should be interpreted with caution because it may reflect normal renal excretion. The significance of increased FDG uptake in clinically silent areas is uncertain.
Disclosure of Interest None declared
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