Patients with Interstitial Lung Disease (ILD) without a definitive diagnosis of connective tissue diseases (CTD) were historically described as Undifferentiated Connective Tissue Disease (UCTD-ILD). Recently a new classification, Interstitial Pneumonia with Autoimmune Features (IPAF), has been proposed. Aim of this study was to describe the prevalence, clinical characteristics and prognostic factors of UCTD and IPAF subjects in a cohort of Non-Specific Interstitial Pneumonia (NSIP) patients. This retrospective, observational study enrolled 102 adult patients characterized by NSIP pattern on High Resolution Computed Tomography, without a specific diagnosis of CTD. Three groups were identified according to patients' characteristics: IPAF, UCTD or idiopathic NSIP (iNSIP). Forty percent, 27% and 55% of patients showed diagnostic criteria for IPAF, UCTD and iNSIP, respectively. No significant differences in age, gender, smoking habit, pulmonary function tests and three-year survival rate were observed among study groups. IPAF patients with antisynthetase antibodies positivity, in comparison to IPAF without antisynthetase antibodies positivity, showed more frequently an acute onset (44% vs 9%, p<0.012). The presence of autoimmune features seems not to be associated with better outcomes in NSIP patients. IPAF criteria seem to be more representative than UCTD criteria in identifying patients with autoimmune features. Further studies are needed to verify if IPAF should include patients with positive antisynthetase serology.
Keywords: Interstitial lung diseases; antisynthetase syndrome.; connective tissue diseases; interstitial pneumonia with autoimmune features; non-specific interstitial pneumonia.