Background The prognosis of Sjögren’s syndrome (SS) is generally better than that of systemic lupus erythematosus (SLE). But, if SLE develops later in SS patients, it could be one of the factors that increase the mortality of SS. Therefore, we determined the impact of demographic factors, clinical manifestations, disease activity, and serological tests at baseline on future SLE development in SS patients.

Methods This retrospective study assessed 1,082 SS patients without other autoimmune diseases at baseline who visited our hospital between January 2012 and March 2021. We analyzed demographic features, extra-glandular manifestations (EGMs), clinical indices, and laboratory values at baseline between the two groups divided per future SLE development (SS/SLE group vs. SS group). The probability and predictors of SLE development in SS patients were estimated using the Kaplan-Meier method and Cox proportional hazards models.

Results The median follow-up duration was 1083.5 days. Forty-nine patients (4.5%) developed SLE that met the 2012 Systemic Lupus International Collaborating Clinics or 2019 EULAR/ACR classification criteria. The baseline EULAR SS disease activity index (ESSDAI) score was significantly higher in the SS/SLE group (p<0.001). The SS/SLE group had more lymphadenopathy and renal involvement (p=0.015 and p=0.017, respectively). Shorter SS disease duration (<3 years) (hazard ratio [HR]=2.61, p=0.012), high ESSDAI (HR=3.04, p=0.024), leukopenia (HR=2.20, p=0.017), hypocomplementemia (HR=17.40, p<0.0001), and positive for anti-dsDNA (HR=19.93, p<0.0001), anti-ribonucleoprotein (RNP) (HR=2.96, p=0.025), and anti-ribosomal P (HR=2.74, p=0.048) at baseline were SLE development predictors in SS patients.

Conclusions Shorter disease duration and higher disease activity of SS at baseline may be risk factors for future SLE development. Serologic predictors of SLE development are hypocomplementemia, leukopenia, and positivity for anti-dsDNA, anti-RNP, and anti-ribosomal P antibodies. If the above factors are observed, close monitoring will be necessary during the follow-up period, considering the possibility of future SLE development.