Characterization of a subset of patients with primary Sjögren's syndrome initially presenting with C3 or C4...

This study aimed to determine the association of C3 and C4 hypocomplementemia at the diagnosis of primary Sjögren's syndrome (pSS) with clinical manifestations, disease activity, and disease damage.

A cross-sectional study was conducted in 94 Puerto Ricans with pSS. Patients were aged ≥21 years and met the 2012 American College of Rheumatology Classification Criteria for pSS. Demographic characteristics, health-related features, cumulative extraglandular manifestations, serologic tests at pSS diagnosis, comorbidities, disease activity (per European League Against Rheumatism Sjögren's Syndrome Disease Activity Index [ESSDAI]), disease damage (per Sjögren's Syndrome Disease Damage Index [SSDDI]), and pharmacologic therapy were determined. Serum C3 and C4 levels were measured at pSS diagnosis by immunoturbidimetry. Patients with and without hypocomplementemia were analyzed using bivariate and multivariate logistic regression analyses adjusted for age, sex, and disease duration.

The mean age and disease duration of the study population were 52.4±12.4 years and 5.9±4.8 years, respectively; of the total study population, 94% were female. C3 and C4 hypocomplementemia were observed in 9.6% and 13.8% of the patients, respectively. In the multivariate analysis, C3 hypocomplementemia was associated with leukocytoclastic vasculitis, interstitial lung disease, higher SSDDI score, and exposure to rituximab. C4 hypocomplementemia was associated with leukocytoclastic vasculitis, interstitial lung disease, and higher ESSDAI and SSDDI scores.

In this population of patients with pSS, low C3 and C4 levels at diagnosis were associated with extraglandular manifestations such as vasculitis and interstitial lung disease, as well as disease activity and damage accrual. These results suggest that complements C3 and C4 have clinical and prognostic value in patients with pSS.