Definition
Nonspecific interstitial pneumonia (NSIP) is a form of interstitial lung disease. On histology, it shows a temporally uniform interstitial process with varying proportions of interstitial inflammation and fibrosis.
By definition, NSIP cases are those that cannot be classified into one of the other categories of idiopathic interstitial pneumonia (usual interstitial pneumonia [UIP], acute interstitial pneumonia [AIP], desquamative interstitial pneumonia/respiratory bronchiolitis–associated interstitial lung disease [DIP/RB-ILD], organizing pneumonia [OP], lymphoid interstitial pneumonia [LIP]).