Purpose of review: 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.
Recent findings: 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.
Summary: 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.