Acute interstitial pneumonia (AIP) is a rare and fulminant form of diffuse lung injury originally described by Hamman and Rich in 1935 [1,2]. AIP is classified as an idiopathic interstitial pneumonia (IIP), and among the IIPs, it has the most acute onset and rapidly progressive course [1-3].
AIP is similar in presentation to the acute respiratory distress syndrome (ARDS) and probably represents a subset of cases of idiopathic ARDS . (See "Acute respiratory distress syndrome: Clinical features and diagnosis".)
The clinical presentation, diagnosis, treatment, and prognosis of AIP will be reviewed here. The other idiopathic interstitial pneumonias and the approach to patients with interstitial lung disease are discussed separately. (See "Idiopathic interstitial pneumonias: Clinical manifestations and pathology" and "Approach to the adult with interstitial lung disease: Clinical evaluation" and "Approach to the adult with interstitial lung disease: Diagnostic testing".)
AIP generally affects previously healthy individuals without a prior history of lung disease and occurs with roughly equal frequency in men and women [5-8]. It is not associated with cigarette smoking. Most patients are over the age of 40 years, with a mean age of 50 to 55 years [3,5,6,8,9].
AIP has the histopathologic appearance of diffuse alveolar damage (DAD) . DAD is a reaction pattern that occurs in response to a number of known causes of lung injury, but in the case of AIP, it is idiopathic (table 1) . DAD has characteristic temporal phases in its evolution — acute exudative, organizing proliferative, and healed (or fibrotic) phases (table 2) [3,6]. (See "Idiopathic interstitial pneumonias: Clinical manifestations and pathology".)