Schematic representation of clinical disease courses in patients with IPF. There are several possible disease courses in patients with IPF. Patients may experience rapid disease progression (line A) or a much more gradual progression of disease (line C), while some patients exhibit periods of relative stability punctuated by periods of acute worsening (stars) (line B). Where the cause of the acute deterioration cannot be identified, the deterioration is termed an acute exacerbation of IPF. Reproduced from Ley B, Collard HR, King TE Jr: Clinical course and prediction of survival in idiopathic pulmonary fibrosis. Am J Respir Crit Care Med 2011, 183:431–440. Reprinted with permission of the American Thoracic Society. Copyright © 2013 American Thoracic Society.