Over the last several years, the clinical-radiologic-pathologic classification of idiopathic interstitial pneumonias (IIPs) has undergone fine-tuning and some remodeling to define discrete identities for these diseases. Publication in 2002 of the American Thoracic Society/European Respiratory Society International Multidisciplinary Consensus Classification scheme1–
represented an important milestone in this process. In this scheme, provisional criteria for diagnosis of idiopathic nonspecific interstitial pneumonia (NSIP) were provided, with recognition that additional investigation was necessary to solidly establish the characteristics of this process and its relationships to other IIPs. At about the same time, the existence of a relationship between NSIP and usual interstitial pneumonia (UIP) was suggested by Flaherty et al.2
These investigators discovered that 26% of patients receiving multilobar surgical lung biopsy for suspected idiopathic pulmonary fibrosis (IPF) had “discordant UIP” (NSIP in at least one lobe and UIP in at least one lobe), and that patients with a discordant UIP pattern had survival more closely resembling concordant UIP (UIP pattern in all lobes) than concordant NSIP (NSIP pattern in all lobes). Although survival for the discordant UIP group was slightly better than that of the concordant UIP group for the first 5 years, the survival curves intersected between 5 years and 6 years.