Lung involvement in primary Sjögren's syndrome: Correlation between high-resolution computed tomography score and mortality

Background: Lung involvement is one of the major systemic manifestations of primary Sjögren's syndrome (pSS). This study aims to demonstrate the correlation between high-resolution computed tomography (HRCT), pulmonary function test (PFT) results, and outcome in these patients. Methods: Forty-four pSS patients were enrolled and their PFT results and HRCT findings/scores were retrospectively investigated. Results: All patients had reduced carbon monoxide-diffusing capacity (DL_CO; <75% of the predicted value); <60% of the predicted value of peak expiratory flow (PEF), of forced vital capacity (FVC), and of forced expiratory volume in the 1st second (FEV₁) were noted in 15 (34.1%) patients, 13 (29.5%) patients, and 12 (27.3%) patients, respectively. HRCT scores had a negative correlation with DL_CO (r = -0.376, p = 0.012), but not with other PFT results. Twelve patients (27.3%) expired during a mean follow-up of 3.7 years; 11 (91.7%) patients died of respiratory failure in the lung-involved patients, of which three were present with pneumonia. The expired patients had lower predicted values of FEV₁ (63.1 ± 19.4% vs. 79.0 ± 22.7%, p = 0.017), FVC (58.7 ± 20.4% vs. 77.1 ± 17.5%, p = 0.005), and PEF (54.3 ± 20.5% vs. 72.0 ± 24.8%, p = 0.035), and higher HRCT scores (9.2 ± 5.7 vs. 5.2 ± 3.5, p = 0.033) than those patients who survived. Patients with FEV₁, FVC, PEF < 60% of the predicted value, or high HRCT score (13-18) presented shorter median overall survival (p = 0.005, p < 0.001, p = 0.021, p < 0.001, respectively). Multivariate analysis adjusted for PFT results showed that HRCT ≥13 was an independent risk factor for mortality (p = 0.007). Conclusion: The clinical outcome of pSS patients with lung involvement in Taiwan is not very favorable. Although HRCT score was poorly correlated with PFT, high HRCT score was significantly associated with higher mortality.