Background Giant Cell Arteritis (GCA) is a large vessel vasculitis, which can occur concomitant with Polymyalgia Rheumatica (PMR). Both diseases may also be seen as isolated disease entities. The two conditions are treated differently, and therefore correct diagnosis is essential. Positron-emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) is receiving increasing attention in the diagnostics of both GCA and PMR (1, 2). In GCA FDG uptake is often seen in the large vessels of the thorax and neck – hereafter called vasculitis pattern (1). In isolated Polymyalgia Rheumatica (PMR) uptake can be seen in the ischial tuberosities, the greater trochanters, and the lumbar spinous processes – hereafter called PMR pattern (3). Temporal artery biopsy is part of the diagnostic workup when GCA is suspected, confirming the diagnosis if characteristic vasculitis histology is found.
Objectives To describe the sensitivity and specificity of vascular FDG uptake on PET-CT compared to temporal artery biopsy result, in suspected GCA and/or PMR.
Methods In a cross-sectional retrospective study design, all patients with the diagnosis GCA and/or PMR attending our rheumatologic ambulatory as of 1 of December 2013 were included. At time of disease presentation, temporal artery biopsy description, treatment start, date of FDG PET-CT and description were registered. Patients were classified according to arterial biopsy (normal or vasculitis) and PET-CT FDG uptake pattern (normal, PMR or vasculitis). If there was FDG uptake in the major vessels, this classified as vasculitis pattern, regardless of coexisting PMR pattern.
Results Information about 118 patients was retrieved. 83 of these had been diagnosed with isolated PMR, and 36 with GCA with or without PMR. 32 patients had undergone both FDG PET-CT scan and temporal artery biopsy at presentation (19 PMR and 13 GCA). The following PET-CT FDG uptake patterns were found: 5 Normal, 15 with PMR and 12 with vasculitis. Three with biopsy verified vasculitis had received glucocorticoids before PET-CT (1 with vasculitis pattern, 1 PMR pattern and 1 normal). Table 1 relates the temporal biopsy description with PET-CT FDG uptake pattern. PET-CT FDG vasculitis uptake had a sensitivity of 78% (7/9) and a specificity of 78% (18/23). The positive and negative predictive value was 58% (7/12) and 90% (18/20), respectively.
Conclusions This study shows that FDG PET-CT, as a measure of vascular involvement in suspected GCA and/or PMR, should be used with caution.
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Acknowledgements Just S.A and Gildberg-Mortensen R. contributed equally to this work.
Disclosure of Interest None declared