Usefulness of 18F‐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 18F‐labeled fluorodeoxyglucose (18F‐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 18F‐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 (SUVmax) (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 SUVmax. 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 SUVmax 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 SUVmax in the parotid glands of ≥4.7 and/or the presence of focal lung lesions are associated with the diagnosis of lymphoma.