Interstitial lung diseases (ILD) represent a frequent complication of connective tissue diseases (CTDs), especially systemic sclerosis, idiopathic inflammatory myopathies and rheumatoid arthritis. ILD can either occur during CTD course or be the first manifestation of CTDs. Therefore screening patients with ILD for CTD is crucial. In some cases, ILD are associated with clinical and/or serological autoimmune features but not classifiable for CTDs. Evolution of these forms to defined CTDs has never been study. Recently, the European Respiratory Society/American Thoracic Society experts proposed a new term, "interstitial pneumonia with autoimmune features" or IPAF, to describe these patients according to updated classification criteria. Aims of this study were to compare CTD occurence during follow-up between IPAF and non-IPAF patients in a idiopathic interstitial pneumonia cohort and to identify risk factors of CTD progression in IPAF patients at diagnosis.

Inclusion Criteria:

• Patients with a new diagnosis of ILD confirmed by two chest-HRCT 3 months apart
• Patients with a minimal follow-up duration of 3 years after ILD diagnosis

Exclusion Criteria:

• Patients with a defined CTD at ILD diagnosis
• Patients with an other ILD etiology identified at diagnosis (i.e. sarcoidosis, hypersensitivity pneumonitis)

Patients with idiopathic interstitial pneumonia classifiable or not as IPAF