THU0358 Usefulness of 18f-fdg positron emission tomography (PET) for lymphoma diagnosis in patients with primary sjÖgren’s syndrome
Authors: J. Keraen, E. Blanc, F. Besson, M. Meyer, V. Le Guern, G. Nocturne, J. Henry, R. Belkhir, X. Mariette, R. Seror
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Primary Sjögren's syndrome (pSS) is the autoimmune disease having the highest risk of lymphoma. The differential diagnosis between benign and malignant lymphoproliferation is sometimes difficult. Among imaging procedures, 18F-FDG PET could be useful for that purpose. <h3>Objectives</h3> To compare 18F-FDG PET results between patients with and without lymphoma to identify PET pattern associated with lymphomas in pSS <h3>Methods</h3> Retrospective study conducted in 2 centres including pSS patients (according to ACR/EULAR 2016 criteria) who undergo 18F-FDG PET. We compared PET abnormalities in patients with and without lymphoma, the PET having been done before any chemotherapy. Two independent readers analysed PET blind to lymphoma diagnosis. ESSDAI-PET score previously described by Cohen <i>et al.</i>[<sup><sup>1</sup></sup> was calculated. <h3>Results</h3> 45 patients were included; 15 had lymphoma: MALT (n=12), nodal marginal zone with plasmacytic differentiation (n=2), diffuse large B-cell (n=1). Patients with lymphoma had more frequently parotid gland swelling (67% vs 20%, p=0.003) and higher ESSDAI score (24 [13.5–29] vs 9,<sup><sup>5–20</sup></sup> p=0.03), even after exclusion of lymphoma item (19<sup><sup>11–27</sup></sup> VS 9,<sup><sup>5–20</sup></sup> p=0.03). Compared to non-lymphoma patients, mean size (45.5<sup><sup>38–56</sup></sup> mm vs. 40<sup><sup>37–41</sup></sup> mm; p=0.048) and maximum standardised uptake value (SUVmax) of the parotid glands (5.6 [5–6.9] vs 3.8 [3.2–4.4]; p=0.001) were higher in lymphoma patients. 53.3% of patients with lymphoma and 43.3% without lymphoma had lymph node FDG uptake, but neither their number nor their repartition or mean SUV differ between them. Pulmonary uptake was observed in 6 (40%) patients with lymphoma and 6 (20%) without lymphoma (p=0.17). But in lymphoma patients, this uptake was focal in 5 (33.3%) patients (nodules or condensation) c and in only one (3.3%) patient without lymphoma (p=0.01). Remaining patients had interstitial FDG uptake. Mean PET score (4<sup><sup>2–4</sup></sup> vs. 2<sup><sup>1–3</sup></sup> p=0.04) and SUVmax at any site (6.3 [5.6–7.3) vs. 4.2 [3.7–5.9] p=0.02) were significantly higher in lymphoma group. 20 patients had PET guided biopsy of a hypermetabolic lesion that conducted to lymphoma diagnosis in 7 cases (46.6%). After chemotherapy for lymphoma, PET was available for 10 patients: complete regression of hypermetabolic lesions was observed in 6 patients (60%), and decreased uptake intensity in the 4 remaining patients. <h3>Conclusions</h3> Some of the systemic manifestation of pSS (lung, lymph nodes and salivary glands) can be assessed by 18F-FDG PET. Lymph nodes hypermetabolism is frequent and not associated with lymphoma. The 18F-FDG PET abnormalities associated with lymphoma diagnosis are SUV max at any site &gt;6, SUV max of parotid glands&gt;5 and focal nodular hypermetabolic lung lesions. Finally, PET can be helpful to guide biopsy toward the most hypermetabolic structure for diagnosing lymphoma. <h3>Reference</h3> [1] Cohen C, Mekinian A, Uzunhan Y, Fauchais A-L, Dhote R, Pop G, et al. 18F-fluorodeoxyglucose positron emission tomography/computer tomography as an objective tool for assessing disease activity in Sjögren's syndrome. Autoimmun Rev. 2013Sep;12(11):1109–14. <h3>Disclosure of Interest</h3> None declared