Nonspecific interstitial pneumonia and usual interstitial pneumonia: comparison of the clinicopathologic features and prognosis

Background: Nonspecific interstitial pneumonia (NSIP) has recently been proposed as a histologic type of idiopathic interstitial pneumonia (IIP), but its broad spectrum of clinicopathologic findings and variable prognosis are poorly understood. It is particularly unclear how NSIP and usual interstitial pneumonia (UIP) are related. The present study investigated the clinicopathologic features and prognosis of NSIP, and its differential diagnosis from UIP. Methods: The clinicopathologic findings and prognosis in 21 NSIP and 18 UIP patients who underwent surgical or video-assisted thoracoscopic lung biopsy were reviewed. Results: NSIP was more frequent in women and showed nonspecific clinical manifestations. High-resolution computed tomography (HRCT) demonstrated ground-glass, net-like, and patchy attenuation in both lungs. Semiquantitative HRCT showed a median fibrosis score of 3 (range, 0 to 7) in NSIP patients and 5 (range, 2 to 7) in UIP patients (P<0.01). On histopathologic examination, NSIP cases were heterogeneous and the findings could be categorized into cellular and fibrosing patterns. The mean age of the NSIP and UIP patients was 48 and 60 years, respectively. The frequencies of fibroblast foci, myogelosis, honeycomb lesions, and pulmonary structural destruction in NSIP and UIP patients were 16.7% and 100% (P<0.001), 22.2% and 85.7% (P<0.05), 16.7% and 92.9% (P<0.001), and 27.8% and 100% (P<0.05), respectively. The responses to glucocorticoid treatment and the prognosis were significantly greater in NSIP than those in UIP. Conclusions: NSIP was difficult to be differentiated from UIP by general clinical manifestations, but HRCT can be helpful for this purpose. Definitive diagnosis depends on the results of surgical lung biopsy.