Cryptogenic organizing pneumonia: clinical outcomes of 60 consecutive cases.

Background: Cryptogenic organizing pneumonia (COP) improves rapidly following corticosteroid treatment; however, relapse is common. Therefore, this retrospective observational study aimed to clarify the clinical outcomes of COP and identify the predictive factors for relapse. Methods: The laboratory findings, pulmonary function test results, computed tomography (CT) findings, and clinical outcomes of 60 consecutive COP patients treated at our institution between 2007 and 2013 were retrospectively reviewed. The clinical characteristics of COP patients who did and did not show improvement were compared to identify the predictive factors for relapse in patients showing improvement. Results: Forty-one patients showed improvement without relapsing (Group 1), whereas thirteen relapsed after showing improvement (Group 2). Six patients did not show any improvement (Group 3). The serum Krebs von den Lungen-6 (KL-6) levels in Group 3 were greater than those in Groups 1 and 2 (P=0.004). The incidence of traction bronchiectasis and reticular opacities in Group 3 was higher than that in Groups 1 and 2 (P=0.048 and P=0.006, respectively). The cut-off levels of C-reactive protein (CRP), blood neutrophil fraction (%neutrophils) and lymphocyte fraction (%lymphocytes) for predicting relapse were 6.84 mg/dL, 68.7% and 14.1% in Groups 1 and 2, respectively. The log-rank test revealed that high serum CRP levels (P<0.001), high %neutrophils (P=0.003) and low %lymphocytes (P=0.006) showed significant correlations with a shorter time to the first relapse episode. Conclusions: Chest CT findings depicting pulmonary fibrosis and high serum KL-6 levels were correlated with the non-improvement of COP. Blood test results indicating inflammatory reactions were correlated with relapse in patients with COP showing improvement.