The alphabet soup revisited: the chronic interstitial pneumonias in the 1990s.

Liebow classified the idiopathic interstitial pneumonias as usual (UIP), desquamative (DIP), bronchiolitis obliterans (BIP), lymphoid (LIP), and giant cell (GIP) interstitial pneumonias. This classification was modified to exclude LIP and GIP. UIP, the most common type, is characterized by synchronous foci of inflammation, collagen deposition, and fibrosis with interspersed normal lung. It usually affects men 40-60 years old and manifests radiologically with bilateral, basilar irregular opacities and volume loss. In most cases, a confident diagnosis can be made at high-resolution computed tomography because of characteristic subpleural irregular linear opacities, ground-glass opacities, honeycombing, and traction bronchiectasis. DIP affects younger patients and is characterized by diffuse intraalveolar macrophage aggregation. Typical radiologic features include bilateral, basilar ground-glass opacities and preserved lung volumes. BIP, renamed bronchiolitis obliterans with organizing pneumonia, affects middle-aged patients and manifests with multifocal plugs of immature fibroblasts in the air spaces. Typical radiologic features include bilateral consolidations and normal lung volumes. Recently described entities include acute (AIP) and nonspecific (NIP) interstitial pneumonias and respiratory bronchiolitis with interstitial lung disease (RB-ILD). AIP is a rapidly progressive, often fatal, illness characterized by diffuse alveolar damage and manifests with clinical and radiologic features of adult respiratory distress syndrome. NIP is a heterogeneous group of fibrosing disorders that cannot be otherwise classified. RB-ILD is a disease of smokers with a good prognosis.