Background: Cryptogenic organizing pneumonia (COP) is a rare lung condition affecting the bronchioles and alveoli. This study aimed to determine the course of the disease and response to treatment in a group of COP patients.
Materials and Methods: In a cohort study, patients' data including demographic features, chest imaging, spirometry, and blood tests, were recorded. Inclusion criteria were radiological features compatible with COP, confirmed tissue biopsy, and the absence of underlying diseases at the time of presentation. All patients received the same steroid-based regimen (oral prednisolone with a dosage of 1 mg/kg tapered to none within 6 months). They were followed for 3 years.
Results: Sixteen patients were included, 43.75% were male. The mean age was 56 ± 15 years. Nobody experienced recurrence. Reversed halo sign and ground-glass opacity were the most common radiological findings. ESR decreased significantly after treatment (P<0.005).  Forced vital capacity increased significantly after treatment (P<0.005), the same was true for oxygen saturation (P<0.005). On three years of follow-up, 5 patients developed signs and symptoms of connective tissue diseases and malignancy. There was no significant association between the final diagnosis and radiological findings at presentation (P>0.05).
Conclusion: Standard treatment in patients with early diagnosis of COP was associated with an appropriate therapeutic response and no recurrence of pulmonary symptoms. Proper treatment can lead to optimized oxygenation parameters and a decreased inflammatory index. Lower response to treatment among corticosteroid-treated COP patients may suggest secondary causes of organizing pneumonia.