SAT0557 RESIDUAL DISEASE ACTIVITY IN ADULT-ONSET STILL’S DISEASE: QUALITATIVE AND QUANTITATIVE ANALYSIS OF A SERIES OF 18F FDG-PET/MR
Authors: S. Bindoli, P. Galozzi, F. Magnani, G. Abruzzino, D. Cecchin, P. Sfriso
Journal: Annals of the Rheumatic Diseases (2020)

Background: Adult-onset Still’s disease (AOSD) is a systemic autoinflammatory disorder characterized by episodes of spiking fever, the presence of an evanescent pink-salmon rash, arthritis/arthralgias, sore throat and increased inflammatory serum markers. The diagnosis is clinical and needs the exclusion of potential mimickers such as infections and lymphoproliferative disorders. Currently, a specific diagnostic test to assess the disease activity is not available. Objectives: To define the residual disease activity in AOSD and establish a possible response to therapy through 18 F-FDG PET/MR imaging technique. Methods: 23 patients affected by AOSD and 24 controls underwent 18 F-FDG PET/MR between 2014 and 2018. A total of 54 18 F-FDG PET/MR were analysed. AOSD patients were diagnosed according to the Yamaguchi’s criteria and were in follow-up at the Rheumatology Unit of Padova University Hospital. The controls were chosen among non-AOSD patients with a previous diagnosis of solid tumors (lymphomas excluded). A qualitative analysis of PET/RM carried out by a Nuclear Medicine Specialist and a semiquantitative analysis carried out by measuring SUVs-to-liver (Standardized Uptake Value) for spleen, bone marrow (BM), lymph nodes and pharynx were performed. A SUVmax BM/SUVmean liver higher than 2.09 was set up as significant area of uptake for each organ considered. This threshold was calculated by adding the standard deviation multiplied by 2 at the mean ratio between SUVmax BM and SUVmean liver of the control group. The Pouchot score for disease activity was calculated for each subject. The distribution of the variables was investigated by Shapiro-Wilk test. The analysis of the association between the variables was carried out using the Mann-Whitney U test. Results: AOSD patients present areas of focal 18 F-FDG uptake mainly in BM, lymph nodes, pharynx, spleen and salivary glands. Sites of uptake in spleen were found in 3.3% of PET/MR, in BM in 23.3%, in lymph nodes in 23.3% and in pharynx in 36.6% of PET/RM respectively. Eleven/thirty (47.8%) patients were defined as “positive” since the uptake was higher than liver, and twelve/thirty (52.2%) were defined as “negative” since the uptake was lower than liver, regardless of SUVs and clinical manifestations. A semi-quantitative analysis assessed whether the values of the SUVmax BM/liver were higher than the cut-off of 2.09 in “positive” PET/MR and lower in the “negative” ones and if the clinical manifestations were present or absent in agreement with the evaluation of SUVs for each patient. BM was found to be active (SUVmax ratio &gt; of 2.09) in 7 out of 11 patients when the PET/MR was defined “positive”, while only in 1 case out of 12 BM SUVmax was &gt;2.09 when the exam was “negative”. Clinical manifestations were present in 10 out of 11 AOSD with a “positive” scan and in 7 out of 11 with both a “positive” scan and a SUV max BM/liver &gt;2.09. Clinical manifestations were present in 1 out of 12 patients with a “negative” scan, while in 10 out of 12 cases with both a negative scan and a SUV max BM/liver &lt;2.09 were absent. Six patients repeated PET/MR during follow-up. The values of the SUVmax BM/liver significantly decreased after anti IL-1β treatment with anakinra. In two cases in which anakinra was deferred, the BM SUVmax values exceeded the cut-off of 2.09 despite the patients did not complain any symptom or inflammation markers increase. Conclusion: 18 F FGD-PET/MR could be able to evaluate the disease activity in AOSD when clinical manifestations and serum markers are not sufficient to establish it. The uptake on BM seems quite sensitive in pointing out the disease severity and in assessing the response to anti IL-1β therapy. 18 F PET/MR is an accurate and repeatable method, however further studies are required to validate its applicability in routinary clinical practice. Disclosure of Interests: None declared