Purpose: The clinical significance of proteinase-3-antineutrophil cytoplasmic antibody (PR3-ANCA) positivity is not well established in idiopathic interstitial pneumonia (IIP) patients. We aimed to determine the clinical features of PR3-ANCA-positive IIP patients.
Methods: We retrospectively reviewed 377 consecutive IIP patients; of these, 360 patients had PR3-ANCA and myeloperoxidase-antineutrophil cytoplasmic antibody test results available. The clinical features of PR3-ANCA-positive IIP patients and control ANCA-negative idiopathic pulmonary fibrosis patients (ANCA-negative IPF) were compared.
Results: Sixteen patients (4.4 %) were PR3-ANCA-positive IIP and 94 (26 %) were ANCA-negative IPF. The median age at diagnosis (72 vs. 70 years, P = 0.17) and proportion of males (75 vs. 89 %, P = 0.12) in PR3-ANCA-positive IIP and ANCA-negative IPF patients, respectively, were not significantly different. Radiologically, the HRCT patterns of PR3-ANCA-positive IIP patients varied (UIP, n = 3, 18.8 %; possible UIP, n = 3, 18.8 %; NSIP, n = 5, 31.3 %; unclassifiable CT pattern, n = 5, 31.3 %) more than those of ANCA-negative IPF patients (UIP, n = 69, 73.4 %; possible UIP, n = 25, 26.6 %; P < 0.001). No PR3-ANCA-positive IIP patients developed ANCA-associated vasculitis. The 5-year survival rate was 50 % in PR3-ANCA-positive IIP patients and 52 % in ANCA-negative IPF patients with no significant difference (P = 0.96 by log-rank test).
Conclusions: The HRCT patterns of PR3-ANCA-positive IIP patients varied more than those of the IPF patients, but the clinical features of high IIP-onset age and male predominance were similar between the groups. Furthermore, PR3-ANCA-positive IIP patients had a poor prognosis similar to that of IPF patients.
Keywords: ANCA; ILD; Interstitial lung disease; Interstitial pneumonia; PR3-ANCA; Proteinase-3-antineutrophil cytoplasmic antibody.