Is high IgG level associated with disease activity and organ damage in patients with Sjögren’s syndrome? A 3-year follow-up cohort study

Hypergammaglobulinemia is prevalent in primary Sjögren's syndrome (pSS) and is considered a marker of disease activity. However, limited data exist regarding its association with disease activity and organ damage. We enrolled patients with pSS from the Chinese Rheumatism Data Centre and categorized them into four groups based on the IgG levels over a 3-year follow-up: consistently high, consistently intermediate, consistently normal, and intermittent. Disease activity and organ damage at the end of the third year were compared across these groups. A total of 351 patients were included in this study, all females with a median age of 45 (IQR 35-53) years. The median baseline IgG was 17.2 (IQR 13.4-21.4) g/L. About 40% of the patients with elevated baseline IgG levels remained in the consistently high or intermediate IgG group. Compared to patients with consistently normal IgG levels, those with consistently high IgG levels had higher median SSDDI scores (2 vs. 1, p = 0.014), higher median ESSPRI scores (2.5 vs. 1.7, p = 0.005), more extra-glandular organ manifestations (IRR 2.34, 95%CI 1.48-3.7, p = < 0.001), and more extra-glandular organ damage (IRR 2.06, 95%CI 1.03-4.12, p = 0.040) at the third-year follow-up. No significant differences in extra-glandular involvement were found between the consistently intermediate IgG group and the consistently normal IgG group. The consistently high IgG level, but not the consistently intermediate level, was associated with a greater number of extra-glandular manifestations and increased extra-glandular organ damage.