Background: Although idiopathic nonspecific interstitial pneumonia (NSIP) was initially identified as a provisional diagnosis, the 2008 American Thoracic Society Project concluded that idiopathic NSIP is a distinct form of idiopathic interstitial pneumonia. However, an association between idiopathic NSIP and autoimmune diseases still attracts interest. In this context, a recent study proposed an intriguing concept that idiopathic NSIP is the pulmonary manifestation of undifferentiated connective tissue disease (UCTD). However, this has not been confirmed in a large number of patients with idiopathic NSIP. The present study was conducted to investigate the proportion and characteristics of patients with idiopathic NSIP who meet the criteria for UCTD.
Methods: We reviewed 47 consecutive patients with idiopathic NSIP and examined whether they met prespecified criteria for UCTD. Furthermore, we compared the clinical characteristics between patients fulfilling the UCTD criteria (UCTD-NSIP) and those not meeting them (Non-UCTD-NSIP).
Results: Of 47 patients with idiopathic NSIP, 22 (47%) met the UCTD criteria. Common symptoms associated with connective tissue diseases (CTDs) were skin change (50%) and Raynaud's phenomenon (41%) in UCTD-NSIP. UCTD-NSIP showed a female predominance and significantly higher percentages of lymphocytes with a lower CD4/CD8 ratio in bronchoalveolar lavage than Non-UCTD-NSIP. Interestingly, UCTD-NSIP had a significantly better survival than Non-UCTD-NSIP.
Conclusions: Idiopathic NSIP included subjects who fulfilled the UCTD criteria, and these subjects had different clinical characteristics with significantly better outcome than those who did not meet the criteria. These data suggest that a part, but not all, of patients with idiopathic NSIP show CTD-like features with a distinct prognosis.