Differences in Radiological and Pathological Findings by ANCA-Subtype in ANCA-Positive Idiopathic Interstitial Pneumonias.

Introduction: Anti-neutrophil cytoplasmic antibody (ANCA) seropositivity strongly correlates to ANCA-associated vasculitis. Patients with idiopathic interstitial pneumonias (IIPs) without systemic vasculitis are sometimes ANCA-positive. Radiological and pathological differences between patients with myeloperoxidase (MPO)-ANCA-positive and those with proteinase 3 (PR3)-ANCA-positive IIPs remain unclear. To determine whether high-resolution computed tomography (HRCT) features and pathology findings differ by ANCA subtype in ANCA-positive IIP patients in a national database. Clinical, radiological, and pathological data were examined along with a web-based multidisciplinary discussion.

Methods: We reviewed records of 10 MPO-ANCA-positive and 9 PR3-ANCA-positive IIP patients who underwent HRCT and surgical lung biopsy between April 2009 and March 2014. Pulmonologists, chest radiologists, and pathologists evaluated HRCT scans and pathological findings independently. Patterns were classified using ATS/ERS/JRS/ALAT 2011 guidelines for idiopathic pulmonary fibrosis.

Results: HRCT patterns were definite usual interstitial pneumonia (UIP) (n = 8; 42.1%), possible UIP (n = 6; 31.6%), and inconsistent with UIP (n = 5; 26.3%). Pathological patterns were definite UIP (n = 5; 26.3%), probable UIP (n = 8; 42.1%), possible UIP (n = 4; 21.1%), and not UIP (n = 2; 10.5%). HRCT and pathological patterns did not differ between MPO-ANCA-positive and PR3-ANCA-positive IIPs. Radiological features were reticulation (n = 13; 68.4%), nodules (n = 12; 63.1%), honeycombing (n = 10; 52.6%), and increased attenuation around honeycombing (n = 7; 36.8%). Pathological findings were cysts (n = 12; 63.1%), lymphoid follicles with germinal centers (n = 11; 57.9%), and peribronchiolar wall lymphocytic infiltration (n = 11; 57.9%).

Conclusion: HRCT and pathological patterns did not differ between MPO-ANCA-positive and PR3-ANCA-positive IIPs. This absence of significant differences suggests a similar mechanism underlying both types of interstitial pneumonia.