Clinical, radiological, and pathological evaluation of "NSIP with OP overlap" pattern compared with NSIP in patients with idiopathic interstitial pneumonias. (November 2020) - Enomoto, Noriyuki
Abstract: Background: Nonspecific interstitial pneumonia (NSIP) and organizing pneumonia (OP) are major subtypes of idiopathic interstitial pneumonias (IIPs) and closely related to connective tissue diseases (CTDs). "NSIP with OP overlap" is a controversial finding that has recently appeared in the criteria of interstitial pneumonia with autoimmune features (IPAF). However, details of this controversial entity are not well known. Objective: To determine the frequency of "NSIP with OP overlap" pattern in IIPs and to identify differences from idiopathic NSIP (iNSIP). Methods: In 524 patients with interstitial pneumonia from 39 institutes who underwent surgical lung biopsy, 444 were diagnosed as IIPs by a multidisciplinary discussion meeting via a cloud-based integrated database. Among these patients, 44 (9.9%) who had iNSIP and 21 (4.7%) with histopathologically-defined "NSIP with OP overlap" pattern (a pathological NSIP and OP pattern, but without a UIP pattern) were retrospectively studied. Results: Patients with "NSIP with OP overlap" pattern showed a significantly greater extent of consolidation (p < 0.001), more subpleural ground glass attenuation (p = 0.036), and more peripheral + bronchovascular distribution (p = 0.009) on high-resolution computed tomography than those with iNSIP. The incidences of newly-developed CTDs during follow-up was similar between the groups and polymyositis/dermatomyositis was the most frequent CTD in both groups. Nearly half of the patients fulfilled IPAF criteria, but no significant difference was found between iNSIP and "NSIP with OP overlap" pattern (47.7% vs. 42.9, p = 0.712). The incidence of acute exacerbation and the survival rates were similar between the groups. Conclusions: The incidence of "NSIP with OP overlap" pattern is 4.7% in IIPs. The frequency of newly-developed CTDs during follow-up, mainly polymyositis/dermatomyositis, the frequency of acute exacerbation, and the survival rate in "NSIP with OP overlap" pattern are similar to those of iNSIP. Highlights: A controversial disease entity of "NSIP with OP overlap" pattern attracts attention in IPAF criteria. In 444 patients with IIPs, 21 (4.7%) were classified as histopathologically-defined "NSIP with OP overlap" pattern. The frequency of CTDs, mainly PM/DM, and that of acute exacerbation in "NSIP with OP overlap" pattern were similar to those of idiopathic NSIP. Prognosis in patients with "NSIP with OP overlap" pattern was favorable and also similar to that of idiopathic NSIP.