LAUSR

Several diffuse interstitial lung diseases (ILD) may be related with varying frequency and severity to connective tissue diseases (CTD). Currently, there are 3 possible scenarios: ILD in patients with a definitive diagnosis of CTD; CTD initially presenting as ILD; and ILD with subtle manifestations that suggest a possible diagnosis of CTD but for which a diagnosis cannot be established with certainty.1 In recent years, patients who did not meet the diagnostic criteria for characterized CTD, but who showed characteristics suggestive of an underlying autoimmune process have been classified using different terms, such as “undifferentiated connective tissue disease-associated interstitial lung disease (UCTD-ILD)”, “lungdominant CTD”, and “autoimmune-featured ILD”, often with some overlap among the criteria. The lack of clear uniformity has prevented this group from being categorically accepted as an entity and from being considered as a uniform cohort for resolving key issues regarding these patients.2 Identifying CTD in a patient under study for an ILD that is in principle considered “idiopathic” is always a challenging but essential step, considering the prognostic and therapeutic implications of an accurate diagnosis.3,4 The clear need to unify the nomenclature and criteria used to define this group of patients and to promote research prompted a working group of the American Thoracic Society (ATS) and the European Respiratory Society (ERS) to propose the term “Interstitial Pneumonia with Autoimmune Features (IPAF)”.2 The diagnostic criteria proposed were: the presence of interstitial lung disease (on chest high-resolution computed tomography [HRCT] or surgical lung biopsy); the exclusion of an alternative etiology and absence of criteria for a characterized CTD; and the coexistence of at least 2 of the following domains: clinical, serologic and morphological.2 Since this document was published in 2015, several studies have attempted to reclassify different patient series using the diagnostic criteria proposed for IPAF. Most are retrospective studies, con-