FDG-PET/CT Useful for Lymphoma Visualization in Primary Sjögren Syndrome

[¹⁸F]-fluorodeoxyglucose (FDG)-positron emission tomography (PET) accompanied by low-dose or contrast-enhanced computed tomography (CT) may be useful in detecting systemic manifestations in primary Sjögren syndrome (pSS)-associated lymphomas, according to study findings published in Rheumatology.

Researchers retrospectively evaluated PET/CT scans for the presence of pSS-associated lymphomas. Patients diagnosed with pSS who underwent FDG-PET/CT at the University Medical Center Groningen in the Netherlands were included in the study. Cutoff values were determined to differentiate between lymphomas and non-lymphomas.

Of a total of 70 patients, those with (n=26) and without (n=44) lymphomas had a mean age of 58.6±14.9 and 57.3±17.7 years, and 84.6% and 75.0% were women, respectively. Participants were diagnosed with pSS a median of 4.5 and 5.0 years before FDG-PET/CT.

The majority of patients (61%) underwent FDG-PET/CT for a suspicion of lymphoma. A total of 42 of the 70 patients underwent biopsy, and lymphomas were found in the parotid gland (n=17), lacrimal gland/orbita (n=2), lungs (n=2), and lymph nodes (n=2).

Individuals in the lymphoma vs nonlymphoma group had parotid gland visual uptake of at least 2 (88.0% vs 45.5%; P <.001), a greater maximum standardized uptake value (SUV_max; median, 4.86 vs 2.29; P <.001), and greater frontal (median, 4.49 vs 3.32 cm; P <.001) and transverse (median, 3.31 vs 2.62 cm; P =.049) diameters. Individuals in the lymphoma vs nonlymphoma group also had submandibular gland visual uptake of at least 2 (66.7% vs 34.9%; P =.012) and a greater SUV_max (median, 3.32 vs 2.42; P <.001); lacrimal gland visual uptake of at least 1 (28.0% vs 6.8%; P =.029); greater SUV_max in the tonsils (median, 4.18 vs 3.19; P =.022); greater mean standardized uptake value (SUV_mean) in the liver (median, 2.55 vs 2.28; P =.024) and pancreas (median, 1.85 vs 1.62; P =.021); and more visual lung nodules (median, 8 vs 3; P =.015).

The best predictors for lymphoma were parotid gland SUV_max of greater than 3.1 (sensitivity, 76%; specificity, 82%; positive predictive value [PPV], 70%; negative predictive value [NPV], 86%), submandibular gland SUV_max of greater 2.9 (sensitivity, 67%; specificity, 84%; PPV, 70%; NPV, 82%), and the presence of nodular lung lesions (sensitivity, 31%; specificity, 93%; PPV, 73%; NPV, 70%).

The predictive power was enhanced when combined, in which the presence of 1 of the 3 predictors had a sensitivity of 92%, specificity of 67%, PPV of 63%, and NPV of 94%, and the presence of 2 of these predictors had a sensitivity of 75%, specificity of 91%, PPV of 82%, and NPV of 87% for predicting lymphoma.

Study limitations included the lack of generalizability to all patients with pSS, as study participants had relatively active disease.

The study authors concluded, “FDG-PET/CT is able to visualize systemic manifestations in pSS, mostly affecting salivary glands, lymph nodes, lungs and entheses. FDG-PET/CT can assist in excluding pSS-associated lymphomas in patients without any PET abnormalities, which could lead to a reduction of invasive biopsies in [patients with] pSS suspected of having a lymphoma. When a biopsy is needed, FDG-PET/CT can guide to the best biopsy location.”