Table 1—

Key features of the idiopathic interstitial pneumonias, as defined by the American Thoracic Society/European Respiratory Society consensus classification 1

	Idiopathic pulmonary fibrosis	NSIP	Respiratory bronchiolitis-associated ILD	DIP	LIP	Cryptogenic organising pneumonia	Acute interstitial pneumonia
Histological lesion	UIP	NSIP	Respiratory bronchiolitis ILD	DIP	LIP	Organising pneumonia	Diffuse alveolar damage
Key histological features	Patchy subpleural fibrosis with temporal and spatial heterogeneity; fibroblastic foci are typically observed at the leading edge of fibrosis	Temporally homogeneous interstitial fibrosis, often with associated mild-to-moderate interstitial infiltrate	Patchy bronchiolocentric distribution of mild fibrosis, submucosal lymphocytic infiltrate and pigmented macrophages within alveolar ducts	Diffuse macrophage accumulation in distal airspaces with accompanying alveolar septal thickening and inflammation	Dense interstitial lymphoid infiltrate, type II cell hyperplasia and occasional lymphoid follicles	Organising intraluminal fibrosis with patchy but temporally uniform distribution; underlying lung architecture preserved	Temporally uniform lesion with alveolar septal thickening, airspace filling and hyaline membranes; later organisation and fibrosis
Mean age of onset yrs	65	50–55	40–50	40–50	40–50	55	50
Rate of onset	Insidious	Insidious	Insidious	Insidious	Insidious	Subacute	Acute
Prognosis	Poor	Intermediate	Good	Good	Intermediate	Good	Very poor

NSIP: nonspecific interstitial pneumonia; ILD: Interstitial lung disease; DIP: desquamative interstitial pneumonia; LIP: lymphocytic interstitial pneumonia; UIP: usual interstitial pneumonia.