Prognostic Factors in Interstitial Lung Disease Associated with Primary Sjögren’s Syndrome: A Retrospective Analysis of 33 Pathologically–Proven Cases

INTRODUCTION Interstitial lung disease associated with primary Sjögren's syndrome (pSS-ILD) shows several patterns such as nonspecific interstitial pneumonia (NSIP) and usual interstitial pneumonia (UIP). Although UIP is a well-recognized prognostic determinant in idiopathic interstitial pneumonias, whether this is also the case in pSS-ILD is unclear. The objectives of this study were to evaluate the prognostic effect of UIP, and to identify the prognostic factors in pSS-ILD. METHODS A retrospective review of medical records identified 33 consecutive patients with pathologically-proven pSS-ILD. Each patient was classified into each ILD pattern by multidisciplinary analysis. Baseline clinical-radiologic-pathologic characteristics and survival rates were compared between the ILD patterns. Finally, the prognostic factors in pSS-ILD were assessed by univariate and subsequent multivariate analyses using Cox's proportional hazards regression model. RESULTS pSS-ILD patients were diagnosed with NSIP (n = 22) or UIP (n = 11). The median follow-up period was 110 months, and five-year survival rate was 87.3% in the total patient population. The prognosis of the UIP patients was not significantly different from that of the NSIP patients (NSIP to UIP, hazard ratio [HR]: 0.77, 95% confidence interval [CI]: 0.18-3.36, P = 0.73). Multivariate analysis identified PaCO2 (HR: 1.68 per 1 Torr increase, 95% CI: 1.24-2.28, P < 0.01), extent of reticular abnormality on high-resolution CT (HR: 4.17 per 1-grade increment, 95% CI: 1.18-14.73, P = 0.03), and severity of fibroblastic foci (HR: 9.26 per 1-grade increment, 95% CI: 1.74-49.35, P < 0.01) as prognostic factors in pSS-ILD. CONCLUSIONS UIP in pSS-ILD was not related to poorer prognosis than NSIP. Assessment of detailed clinical-radiologic-pathologic findings is more important than distinguishing UIP to evaluate prognosis in this disease.