IPF exacerbations represent acute and clinically signifi cant deteriorations of unidentifi able cause, transform ing the slow and more or less steady disease decline [13] to the unexpected appearance of acute lung injury/ acute respiratory distress syndrome (ALI/ARDS) ending in death [6, 14] . Occasionally, IPF exacerbations may present in a previously apparently healthy or minimally symptomatic individual and might represent acute progression of an unsuspected or undiagnosed early IPF [3, 15] . Defi nition criteria include IPF diagnosis, unexplained worsening or development of dyspnea within 30 days, new lung infi ltrates (mainly ground glass upon honeycomb), and exclusion of any identifi able or treatable cause of lung injury [6] . Surgical lung biopsy per se constitutes a risk factor for their development [16] but, when performed for the investigation of the etiology of exacerbations or in autopsies, discloses a histological picture of diff use alveolar damage (DAD), which is the ARDS tissue counterpart, upon usual interstitial pneumonia (UIP), which is the IPF tissue equivalent [4, 8, [17] [18] [19] .