Alveolar Disease

Diffuse alveolar damage (DAD) is the histopathological substrate for most patients diagnosed clinically with the acute respiratory distress syndrome. The two terms are not synonymous, however, as some patients presenting with acute unexplained respiratory failure will be found to have a more specific disease. The benchmark for DAD is the hyaline membrane. Some authors have used the term acute interstitial pneumonitis for cases where the etiology of the DAD is unknown, and restricted the term DAD to cases where the etiology is known. The disease, when usually sampled, is subacute (weeks), principally alveolar rather than interstitial (alveoli filled by myxoid fibrosis), and not a pneumonitis (principally fibrosis rather than inflammation).