"Usual" interstitial pneumonia with autoimmune features: a prospective study on a cohort of idiopathic pulmonary fibrosis patients.

Objectives: The classification interstitial pneumonia with autoimmune features (IPAF) includes patients with interstitial lung disease (ILD) associated with autoimmune characteristics insufficient to reach classification criteria for a specific autoimmune disease (SAD). These criteria are divided into three domains: clinical, serological and morphological. The latter domain does not include the usual interstitial pneumonia (UIP) pattern, which is deemed not to be significantly associated with SAD. Therefore, the enrolment of these patients is more difficult, requiring at least one item from both of the other domains. The objective of this study is to evaluate the rate of progression towards SAD of a cohort of UIP patients satisfying only one IPAF domain (we called this group "UIPAF") compared with classic idiopathic pulmonary fibrosis (IPF).

Methods: We prospectively enrolled IPF patients with radiologic and/or histologic UIP pattern, followed jointly by rheumatologists and pulmonologists from January 2017 to January 2021, with a minimum follow-up of 12 months.

Results: We enrolled 190 IPF patients, 38 (20%) of whom were classified as UIPAF. IPF and UIPAF patients were similar for general characteristics, severity and prognosis, at presentation and at annual check-up. However, 28.9% of UIPAF patients progressed towards SAD, compared with 2% of IPF patients (χ2=30.4, p≤0.0001).

Conclusions: The association between a single clinical or serological domain of IPAF and UIP pattern is predictive for the development of a SAD if compared with isolated UIP. ILD can be the first manifestation of SAD, even with a UIP pattern, therefore, the morphological domain of IPAF criteria could be removed.