Background Sjögren´s syndrome occurs in isolation (primary Sjögren´s syndrome, pSS), but it is also often secondary (sSS) to, and sometimes difficult to delineate from systemic lupus erythematosus (SLE). Consequently there is a need to investigate similarities and differences between SLE patients with (SLE-sSS) and without sSS (SLE-noSS).
Objective To investigate the occurrence of sSS in a large cohort of SLE patients and to explore clinical and laboratory characteristics associated with SLE-sSS as compared to SLE-noSS and controls.
Methods We included 504 consecutive SLE patients and 322 population controls, matched for age and gender. All patients fulfilled the 1982 revised ACR criteria for SLE. SLE-sSS was defined according to the American-European consensus criteria (AECC). Subjective and objective quantifications of sicca symptoms were recorded. All underwent a thorough clinical investigation. SLE-associated autoantibodies, (ANA screening by BioPlex 2200 system, Bio-Rad) and Rheumatoid factor (Rf, Phadia Immunocap 250) were determined, Routine laboratory workup and a panel of cytokines (MSD 30-plex cytokine assays, performed on samples from 433 consecutive SLE patients and 319 controls) were measured.
Results SLE-sSS, occurred in 23% of the SLE patients. Compared to SLE-noSS the SLE-sSS group was older, both at inclusion (55 vs 43 years, p<0.0001) and at disease onset (40 vs 32 yrs p<0.0001), and more enriched in females (96 vs 83%, p=0.0007), Leucopenia (57 vs 45%, p=0.02) and peripheral neuropathy (15 vs 7%, p=0.01) were more common and nephritis less common (32 vs 43%, p=0.03). Higher levels of total IgG, positivity for anti-SSA/Ro52, anti-SSA/Ro60, anti-SSB antibodies, Rf IgM and Rf IgA characterised the SLE-sSS group. 19/20 levels of detected cytokines were higher in SLE than in controls. 6/20 cytokines (TNF-a, IL-6, MCP-4, MIP-1β, IL12/IL-23p40 and IP-10) were upregulated in SLE-sSS vs SLE-noSS (see table for figures).
Conclusion Frequency of SLE-sSS increases with age and affects roughly ¼ of SLE patients. Nephritis was less common while leucopenia and peripheral neuropathy were more common. We report higher levels of six pro-inflammatory. These findings demonstrate that, though often regarded as a milder version of SLE, patients with SLE-sSS are characterised by a state of chronic systemic inflammation.
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