Reprint of: Nonspecific interstitial pneumonia: pathologic features and clinical implications.

Nonspecific interstitial pneumonia (NSIP) is a form of chronic interstitial pneumonia that should be separated from the other idiopathic interstitial pneumonias, including most importantly, usual interstitial pneumonia (UIP). Diagnosis is predicated on identification of characteristic findings in a surgical lung biopsy in the appropriate clinical and radiological context. Affected patients may have a variety of underlying or associated conditions, although most have a form of idiopathic lung disease associated with a more favorable prognosis than UIP/idiopathic pulmonary fibrosis (IPF). Keys to distinguishing NSIP from UIP include absence of heterogeneous lung involvement, architectural distortion in the form of fibrotic scarring and/or honeycomb change, and fibroblast foci in NSIP.