Nonspecific interstitial pneumonia: a provisional category of idiopathic interstitial pneumonia

Idiopathic interstitial pneumonias (IIP) represent a complex group of relatively rare entities with similar clinical, vaguely similar radiographic and differing histologic features. The recent international multidisciplinary consensus statement produced by the American Thoracic Society/European Respiratory Society aiming to standardize the classification of IIP recognizes nonspecific interstitial pneumonia (NSIP) as a provisional category. While not representing a single disease, but rather a collection of pathologic processes with similar histomorphology, NSIP has been a great source of confusion for pulmonologists, radiologists, and pathologists.

Lacking diagnostic clinical or radiographic features, NSIP is an IIP with recognizable and reproducible morphologic patterns different from usual interstitial pneumonia (UIP)-pattern as well as other disease patterns. And while overlap with UIP-pattern can be seen in individuals with multiple biopsy samples, those with either cellular or fibrosing variants of NSIP have a better prognosis than UIP-pattern patients.

A morphologic diagnosis of NSIP-pattern alerts the clinician to a wide spectrum of potential clinical possibilities and enables researchers to study both this fibrosing interstitial pneumonia pattern and the more common and deadly UIP-pattern separately. Thus, this provisional category is useful to both clinicians and researchers.