Clinical Characteristics and Risk Factors for Progressive Pulmonary Fibrosis in Primary Sjögren's Syndrome: A Case-Control Study.

Objective: This study aims to investigate the clinical characteristics and identify risk factors associated with progressive pulmonary fibrosis (PPF) in individuals diagnosed with primary Sjögren's syndrome (pSS).

Methods: A retrospective case-control study was conducted from individuals with pSS-associated interstitial lung disease (pSS-ILD) registered in the Chinese Rheumatism Data Center between June 2010 and October 2023. Participants were categorized into two groups: those with PPF (pSS-PPF) and those without PPF (pSS-non-PPF). Comparative analyses were performed on clinical manifestations, laboratory parameters, pulmonary function, and treatment history between the two groups.

Results: Sixty-six individuals with pSS-ILD were included, of whom 29 met the criteria for PPF. Compared to pSS-non-PPF group, the pSS-PPF group demonstrated a higher rate of expectoration (48.3% vs 16.2%, p = 0.005) and crackles on auscultation (41.4% vs 13.5%, p = 0.01), but lower rates of parotid gland enlargement (3.4% vs 32.4%, p = 0.003), and arthritis (6.9% vs 27%, p = 0.035). Additionally, the incidence rate of the subjects suffering xerophthalmia and xerostomia in the PPF group was lower (24.1% vs 2.7%, p = 0.023). Pulmonary function testing showed significantly reduced forced vital capacity percentage predicted (83.6±15.6 vs 91.3±14.6, p = 0.042) and diffusing capacity of the lung for carbon monoxide percentage predicted (DLCO%, 54.2±21.5 vs 68.5±13.6, p = 0.003) in the PPF group. Multivariate logistic regression identified a baseline DLCO% < 60% as an independent risk factor for PPF. Parotid gland enlargement and arthritis were potentially protective. The predictive model demonstrated good performance, with an area under the curve of 0.821 (95% CI: 0.716~0.925, p < 0.001). The sensitivity was 58.6% and the specificity was 91.7%.

Conclusion: A baseline DLCO% < 60% is an independent predictor of PPF in individuals with pSS. The developed predictive model shows strong discriminatory ability, while further validation in larger cohorts is warranted.