Definition
Acute interstitial pneumonia (AIP) is an idiopathic interstitial lung disease that is clinically characterized by sudden onset of dyspnea and rapid development of respiratory failure.
AIP is histologically characterized by diffuse alveolar damage with subsequent fibrosis.
The definition of AIP excludes patients with acute respiratory distress syndrome (ARDS) attributable to an identifiable cause, as well as patients with underlying fibrotic lung disease or systemic disorders known to be associated with lung involvement such as connective tissue disease.