Usefulness of ¹⁸ F‐Labeled Fluorodeoxyglucose–Positron Emission Tomography for the Diagnosis of Lymphoma in Primary Sjögren's Syndrome

Objective The usefulness of positron emission tomography–computed tomography ( PET ‐ CT ) with 18 F‐labeled fluorodeoxyglucose ( 18 F‐ FDG ) for the diagnosis of lymphoma in patients with primary Sjögren's syndrome ( SS ) is unclear, since the abnormalities it reveals may be due to systemic manifestations of SS . This study was undertaken to compare 18 F‐ FDG – PET ‐ CT in patients with primary SS with lymphoma and those without lymphoma in order to identify patterns associated with lymphoma. Methods A retrospective study was conducted in 2 centers and included patients who met the American College of Rheumatology/European League Against Rheumatism 2016 criteria for primary SS and had undergone PET ‐ CT . Two independent readers who were blinded with regard to lymphoma diagnosis analyzed PET ‐ CT scans. Abnormalities were compared between patients with and those without lymphoma. Results Of the 45 patients included, 15 had lymphoma. Compared to patients without lymphoma, the mean size ( P = 0.048) and maximum standardized uptake value ( SUV max) ( P = 0.001) of the parotid glands were higher in patients with lymphoma. FDG uptake in the lymph nodes was observed in 53.3% of the patients with lymphoma and 43.3% of the patients without lymphoma, with no difference in the number of sites, uptake pattern, or mean SUV max. Focal pulmonary uptake (nodules or condensations) was observed in 5 of the patients with lymphoma (33.3%) but only 1 patient without lymphoma (3.3%) ( P = 0.01). Having an SUV max in the parotid gland of ≥4.7 and/or the presence of focal pulmonary lesions was highly suggestive of lymphoma (sensitivity 80%, specificity 83.3%). Conclusion Some systemic manifestations of primary SS (lymphadenopathy, pulmonary involvement, and salivary gland involvement) can be visualized by PET ‐ CT . Involvement of the lymph nodes and parotid glands is commonly observed with a similar frequency in SS patients with and those without lymphoma. An SUV max in the parotid glands of ≥4.7 and/or the presence of focal lung lesions are associated with the diagnosis of lymphoma.