Acute exacerbation of idiopathic pulmonary fibrosis: shifting the paradigm. 
The goal of this review is to summarise the clinical features, management, and prognosis of acute exacerbations of idiopathic pulmonary fibrosis (AE-IPF).  AE-IPF has previously been defined based on clinical and radiological features that include the subacute onset of dyspnoea, bilateral ground glass changes on chest high-resolution computed tomography, and the absence of an identifiable aetiology.  The annual incidence of AE-IPF is typically reported at 5-15%, but is less common in mild disease.  Features of diffuse alveolar damage are present when a biopsy is performed.  Idiopathic pulmonary fibrosis (IPF) patients with acute respiratory worsening are often initially treated with high dose corticosteroids and antimicrobials; however, there are no clear data to support these therapies, and the short-term mortality of AE-IPF is ~50%.  Recent studies have shown that the features and prognosis of AE-IPF are similar to other causes of acute respiratory worsening, including infection, aspiration, air pollution and mechanical injury to the alveolar epithelium.  Based on this emerging evidence, we propose a novel approach to the classification of acute respiratory worsening events in patients with IPF that focuses on clinical and radiological findings consistent with an underlying pathobiology of diffuse alveolar damage.