Pulmonary Involvement in Microscopic Polyangiitis: Computed Tomography Findings in 55 Patients With Analysis of Risk Factors for Recurrence

Background and objective Pulmonary involvement is seen in up to 30% of microscopic polyangiitis (MPA) patients. Pulmonary radiological findings for MPA have been scarcely reported to date. This study was conducted to evaluate computed tomography (CT) and clinical findings at the time of MPA diagnosis as predictors for systemic or lung recurrence. Methods We retrospectively reviewed the medical records and radiological data of 55 MPA patients with pulmonary involvement who were admitted to our hospital between April 2008 and December 2016. Results Aside from pulmonary lesions, lesions were found in the kidneys (52.7%), skin (7.3 %), and peripheral nerves (3.6%). Biopsies were performed for 29.1% of the patients, with an overall diagnostic accuracy of 78.9%. Parenchymal opacities (74.5%, mainly ground-glass opacities and reticular shadowing) were more commonly seen than airway abnormalities were (40.0%, mainly bronchiectasis). Systemic recurrence in the first year after diagnosis was found in 10.9% of the patients, and it mainly involved the kidneys or lungs. A serum WBC count ≥ 10,900/μL was a risk factor for predicting systemic recurrence within the first year after diagnosis according to the Cox regression analysis (HR 11.1, 95%CI: 1.3-95.9, p=0.028). Lung recurrence within five years after the diagnosis was observed in 9.1% of the patients. The incidences of reticular shadowing and honeycombing in thoracic CT at diagnosis were significantly higher in recurrence-positive patients than in recurrence-negative patients, but these differences could not be used to predict lung recurrence. Conclusions Ground glass opacities, reticular shadowing, and bronchiectasis are prominent thoracic CT findings for MPA. There are no radiological patterns capable of predicting recurrence. However, a serum WBC count ≥ 10,900/μL at diagnosis might be a predictive factor for systemic recurrence within the year.