Background Sjogren’s syndrome (SS) is a chronic autoimmune disease characterized by lymphocytic infiltration of the exocrine glands. It can be associated with other connective tissue diseases (CTDs), including systemic lupus erythematosus (SLE).

Objectives To determine the incidence of secondary Sjogren (sSS) in patients diagnosed with systemic lupus erythematosus (SLE-SS) and compare clinical and serological features of SLE-SS to SLE-only patients.

Methods We performed a prospective observational study including patients seen at Rheumatology department diagnosed with systemic lupus erythematosus (SLICC criteria) between 1990–2020. A total of 453 patients diagnosed with SLE were assessed for fulfilment of the criteria for SS using: (European questionnaire and Schirmer test), fluorescein staining test/non-stimulated whole-salivary flow, and anti-Ro/La antibodies and lip biopsy. Anti-Ro/SSA and anti-La/SSB antibodies and RF were measured at entry into the cohort and at SS assessment. SS/SLE was defined according to the American-European Consensus Criteria (AECC). We defined as SLE-SS the case that only fulfilled SLE classification criteria at first and then, during follow-up, the disease progressed and met classification criteria for sSS.

Results SLE-sSS, occurred in 11% of the patients with SLE. In comparison to SLE-non sSS, the SLE-sSS group was older at inclusion, onset and with a longer disease course. Sicca syndrome, oral ulcers, pulmonary involvement, and peripheral neuropathy were more frequent. Anti-SSA, anti-SSB, rheumatoid factor and total IgG were higher in the SLE-sSS group (for all comparisons).

Conclusion SLE-SS appears to be a subgroup of patients with distinct clinical and serologic. The frequency of SLE-sSS increased with age. The subset of patients with SLE-SS has higher frequency of oral ulcers, anti-Ro and anti-La antibodies and a lower frequency of renal disease, anti-dsDNA antibodies, anti-SM and lower hypocomplementemia of C3 and C4.