[Clinical criteria for definition of idiopathic interstitial pneumonia (IIP)].

Clinical criteria for definition of IIP proposed in 1991 by the Project Team for Diffuse Lung Diseases Organized by Japanese Ministry of Health and Welfare are reviewed. After the clinical roentgenological, and pathological researches of 92 IIP patients, we concluded that IIP patients were grouped into two clinical types, acute and chronic, by their clinical courses and characteristic pathological findings. The latter is, moreover, grouped into two types, typical and atypical, by their morphological characteristics. The acute type are represented by alveolitis with marked edema and cell infiltration of alveolar wall, and by hyaline membrane formation. "Typical" of chronic types only have typical pathologic changes of interstitial pneumonia and/or fibrosis represented by honeycombing. "Atypical" have both those interstitial changes and intra-alveolar scar formation and fibrosis due to organized pneumonia and secondarily occurred emphysema such as bulla as well. The continuity in clinical courses between acute and chronic types are still obscure.