Clinicopathological study on two types of cryptogenic organizing pneumonitis

Clinical and pathological studies on cryptogenic organizing pneumonitis (COP) were performed in 19 cases diagnosed with transbronchial lung biopsy (TBLB). All patients suffered from fever and several respiratory symptoms. Laboratory data showed increases in erythrocyte sedimentation rate, positivity for C-reactive protein, negative tuberculin reactions and increases in complement level. Pathological findings demonstrated that there were two kinds of organizing processes. Fourteen of the 19 cases were treated with prednisolone, and two cases were observed without administration. The remaining three cases could not be followed up after therapy. In 11 of the 16 cases, abnormal shadows in chest X-ray disappeared, but remained present in five cases. As for the relationship between pathological findings and shadows in chest X-ray, Masson bodies without fibrin were observed in the 11 cases which were without shadows on X-ray, but Masson bodies containing or related to fibrin were observed in the five cases in which abnormal shadows remained. These results suggest that there are two types of organizing process in COP. Type I is an unexplained organizing process in which fibrin is not present or involved. It responds well to steroids and the prognosis is favourable. Type II is an organizing process which involves fibrin, and the character of the fibroblast-like cells is very similar to that of myofibroblasts. Type II organizing process responds poorly to steroids. Both processes can be notified relatively easily, even by TBLB tissues.