State of the art in interstitial pneumonia with autoimmune features: a systematic review on retrospective studies and suggestions for further advances

The term interstitial pneumonia with autoimmune features (IPAF) has been proposed to define patients with interstitial lung disease (ILD) associated with autoimmune signs not classifiable for connective tissue diseases (CTDs). This new definition overcomes previous nomenclatures and provides a uniform structure for prospective studies through specific classification criteria. This work evaluates the characteristics of IPAF patients reported in the literature, to highlight potential limits through a comparative analysis and to suggest better performing classification criteria. Four retrospective studies on the IPAF population have been considered. The study subjects differed in age, sex, smoking habit, ILD pattern and outcomes. Another important difference lies in the diverse items considered in the classification criteria. The retrospective design of the studies and the absence from some of them of a rheumatologist clearly involved in the diagnosis may have influenced the data, but current IPAF criteria seem to include a rather heterogeneous population. To overcome these discrepancies, this review suggests a limitation in the use of single items and the exclusion of extremely specific CTD criteria. This should avoid the definition of IPAF for those diseases at different stages or at early onset. The investigation of a functional or morphological cut-off of pulmonary involvement would be useful.