Clinical features, risk factors, and outcomes of patients with interstitial pneumonia with autoimmune features: a population-based study

To investigate the clinical features, risk factors and outcomes of patients with interstitial pneumonia with autoimmune features (IPAF). A total of 1429 patients with idiopathic interstitial pneumonia (IIP) and undifferentiated connective tissue disease-associated interstitial lung disease (UCTD-ILD) were screened to identify patients who met IPAF criteria. Clinical, serological, and morphological features of patients with IPAF were characterized. Outcomes between patients with IPAF, UCTD-ILD, and IIP who were divided into idiopathic pulmonary fibrosis (IPF) and non-IPF groups were compared using survival as an endpoint. Patients with IPAF were much common in young female and had lower percentage of ever smoking and a significantly shorter survival than those with non-IPAF (P < 0.001). Subgroup analysis revealed that IPAF cohort survival was worse than that in non-IPF (P < 0.001), but better than that in IPF (P < 0.001). In IPAF cohort, the most common systemic symptom and serological abnormality were Raynaud’s phenomenon (12.9%) and ANA ≥ 1:320 (49.2%); the most frequent high-resolution computed tomography (HRCT) pattern was nonspecific interstitial pneumonia (NSIP) (61.6%). Multivariate analysis indicated that several factors including age, smoking history, organizing pneumonia (OP) pattern in HRCT, and anti-RNP positivity were independently associated with significantly worse survival. IPAF had the distinct clinical features and outcomes compared with other groups of ILD. Additional studies should be needed to explore the underlying autoimmune mechanism and to determine risk stratification in future clinical research.