Schematic representation of potential clinical courses of idiopathic pulmonary fibrosis (IPF)

As IPF progresses, there is a subclinical period in which only radiographic findings of disease may be present, followed by a symptomatic period consisting of both pre-diagnosis and post-diagnosis clinical phases. The rate of decline and progression to death may be rapid (line A), slow (lines C and D), or mixed (curve B), with periods of relative stability interposed with periods of acute decline (asterisk).