Objectives: To analyze the clinical and immunological characteristics at enrollment in a large prospective cohort of patients with primary Sjögren's syndrome (pSS) and to investigate the association between serum BAFF, beta2-microglobulin and free light chains of immunoglobulins and systemic disease activity at enrollment.
Methods: Three hundred and ninety five patients with pSS according to American-European Consensus Criteria were included from fifteen centers of Rheumatology and Internal Medicine in the "Assessment of Systemic Signs and Evolution of Sjögren's Syndrome" (ASSESS) 5-year prospective cohort. At enrollment, serum markers were assessed as well as activity of the disease measured with the EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI).
Results: Patient median age was 58 (25(th)-75(th): 51-67) and median disease duration was 5 (2-9) years. Median ESSDAI at enrollment was 2 (0-7) with 30.9% of patients having features of systemic involvement. Patients with elevated BAFF, beta2-microglobulin and kappa, lambda FLCS had higher ESSDAI scores at enrollment (4 - vs 2 [0-7], P = 0.03; 4 - vs 2 [0-7], P< 0.0001); 4 - vs 2 [0-6.6], P< 0.0001 and 4 [2-8.2] vs 2 [0-7.0], P = 0.02, respectively). In multivariate analysis, increased beta2-microglobulin, kappa and lambda FLCs were associated with a higher ESSDAI score. Median BAFF and beta2-microglobulin were higher in the 16 patients with history of lymphoma (1173.3(873.1-3665.5) vs 898.9 (715.9-1187.2) pg/ml, P = 0.01 and 2.6 (2.2-2.9) vs 2.1 (1.8-2.6) mg/l, P = 0.04, respectively).
Conclusion: In pSS, higher levels of beta2-microglobulin and free light chains of immunoglobulins are associated with increased systemic disease activity.