The clinical and laboratory characteristics of Sjögren's syndrome that progresses to systemic lupus erythematosus: a retrospective case-control study.

OBJECTIVE: We investigated the clinical and laboratory characteristics of Sjögren's syndrome-onset systemic lupus erythematosus (SS/SLE), focusing on the possible risk factors of SS that allow development to SLE.
METHODS: The experimental group included 55 SS/SLE patients, and the control group included 55 primary SS (pSS) patients recruited from our department between 1997 and 2012.
RESULTS: Compared with the control group, SS/SLE patients showed a younger age of onset of SS (31 ± 12 vs. 39 ± 11 years, P = 0.001). In clinical characteristics, SS/SLE patients showed a lower frequency of xerostomia (78.2% vs. 96.4%, P = 0.016) and interstitial lung disease (27.3% vs. 54.5%, P = 0.004), and a higher frequency of arthritis (74.5% vs. 40.0%, P = 0.000). In laboratory characteristics, SS/SLE patients showed a higher frequency of leukopenia (56.4% vs. 29.1%, P = 0.004), proteinuria (27.3% vs. 7.3%, P = 0.009), and low complement levels (CH50 : 30.9% vs. 1.8%; C3 : 54.5% vs. 12.7%; C4: 41.8% vs. 7.3%, P = 0.000). The multivariate analysis using logistic regression revealed that age of onset, low levels of C3 and C4 were the independent risk factors of SS/SLE (age of onset: RR = 0.919, P = 0.000; low C3 levels: RR = 9.659, P = 0.000; low C4 levels: RR = 6.035, P = 0.007).
CONCLUSION: The SS/SLE patients had an earlier age of onset, higher incidences of arthritis, leucopenia, proteinuria and low complement levels, and lower incidences of xerostomia and interstitial lung disease compared with pSS patients. These results suggest that we should be vigilant with the pSS patients who have all these mentioned clinical and laboratory characteristics, and are more likely to develop SS/SLE.