Nonspecific interstitial pneumonia (NSIP) has been recognized as a separate histological classification of interstitial lung disease. Similar features are found not only in idiopathic NSIP, but also in NSIP associated with collagen vascular disorder (CVD-NSIP). We examined the clinical symptoms, laboratory findings, and prognosis of 13 cases of idiopathic NSIP and 11 cases of CVD-NSIP. Immunohistochemical staining was performed using the streptavidin/biotin/peroxidase method with anti-alpha-smooth muscle actin antibody. No differences in the distribution of clinical features, laboratory findings, and prognosis were observed between idiopathic NSIP and CVD-NSIP. In immunohistochemical staining of the fibrosing areas, myofibroblasts were observed in 7 of 13 idiopathic NSIP cases, but in 10 of 11 CVD-NSIP cases. With regards to intra-alveolar organization, myofibroblasts were observed in all 10 CVD-NSIP cases, but they were observed in only 2 of 9 idiopathic NSIP cases. We found a significantly higher myofibroblast proliferation in the intra-alveolar organization of CVD-NSIP compared to idiopathic NSIP. Clinically, idiopathic NSIP and CVD-NSIP are similar, but are pathologically different.</p
