Are there differences in the clinical and laboratory features of patients with seronegative primary Sjögren's syndrome?

Background/aim: The objective of this study was to demonstrate the commonalities and distinctions between patients with seronegative and seropositive primary Sjögren's syndrome (pSS).

Materials and methods: The records of 399 patients with pSS seen between January 2010 and June 2023 were retrospectively examined. Patients with negative antiSSA/Ro, antiSSB/La, ANA, and RF antibodies comprised the seronegative group, while patients with at least one positive antibody were included in the seropositive group.

Results: The most common clinical features between the groups were arthralgia (81.2%), arthritis (11.5%), hematological involvement (19.8%), and pulmonary involvement (11.8%). In 41 patients (10.3%), no autoantibody positivity was detected. The number of patients with at least one extraarticular involvement was statistically more frequent in the seropositive group (p = 0.011). Dry mouth was found to be more prevalent among seronegative patients (p = 0.003). While hyperimmune gammaglobulinemia exhibited a higher prevalence within the seropositive group (p = 0.004), the occurrence of reduced complement levels was at similar rates in both groups. All deaths were observed exclusively within the seropositive group (17/358, 4.7%). No difference was observed between the two groups concerning mortality (p = 0.237) and malignancies (seropositive group: 9/358, 2.5% vs. seronegative group: 3/41, 7.3%, p = 0.115). There was a statistically significant association between low C4 levels (OR = 2.99 [1.09-8.16], p = 0.045 in model 1, OR = 3.10 [1.14-8.42], p = 0.022 in model 2), and the extraarticular findings.

Conclusion: While hematological, renal, pulmonary, and neurological involvements are observed with similar frequency in both seronegative and seropositive pSS patients, the presence of extraarticular manifestations was more common in seropositive patients. Additionally, there was a relationship between extraarticular involvement and low C4 levels.