18F-fluorodeoxyglucose positron emission tomography/computer tomography as an objective tool for assessing disease activity in Sjögren's syndrome.

Objective: This study aims to determine the value of FDG-PET/CT to assess disease activity in patients with Sjögren's syndrome (SS).

Methods: Thirty-two patients with SS who underwent PET/CT were retrospectively analyzed. PET/CT activity score was measured using a 6-point scale including the 6 following items (0/1: absence or presence of an item): lymphadenopathy on CT, high-resolution CT (HRCT) evidence of interstitial lung disease (ILD), parotid glands SUVmax >3, submandibular glands SUVmax >3, lymph node uptake, ILD uptake. Combined PET/CT score was correlated to ESSDAI (EULAR Sjögren's Syndrome Disease Activity Index) score and other parameters of SS activity.

Results: Pathological FDG uptake was observed in 75% of patients (24/32): lymph-nodes (n=19, 60%), salivary glands (n=17, 53%), lungs (n=9, 28%), and thyroid (n=2). Median ESSDAI and PET/CT activity scores were 9.5 [5-12] and 2 [0-3], respectively. PET/CT activity score correlated with ESSDAI (r=0.49, p=0.005), unlike SUVmax. Patients with a high ESSDAI score had a higher PET/CT activity score than patients with a low ESSDAI score (3 vs 1, p=0.004). PET was also correlated with gammaglobulin levels (r=0.43, p=0.02), but not with the presence of cryoglobulinemia, activated complement or beta-2 microglobulin levels. The FDG uptake in patients with lymphoma (n=4) was higher than in patients without lymphoma (SUVmax=5.4 vs. 3.2, p=0.05).

Conclusion: We described a new PET/CT activity score, which correlates to ESSDAI and could help to assess disease activity in SS patients. PET can also help in the diagnosis of lymphoma, even if inflammatory lymph nodes can be frequently observed in SS patients.