Pos0253 Progression to Anca-Associated Vasculitis in Patients With Idiopathic Interstitial Pneumonia and Positive Anca Results

Background: Interstitial lung disease (ILD) is a condition characterized by inflammation and fibrosis in the interstitial spaces of the lungs. Affected patients undergo a thorough work-up to identify secondary causes such as drugs or connective tissue diseases (CTDs). When the cause remains unknown, the disease is termed idiopathic interstitial pneumonia (IIP). Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) can lead to ILD, particularly in patients with positive anti-myeloperoxidase (MPO)-ANCA results. However, not all patients with positive ANCA results at the time of ILD diagnosis show the full features of AAV. A recent study showed that up to 23% of patients with granulomatosis with polyangiitis (GPA) and 45% of patients with microscopic polyangiitis (MPA) exhibit ILD during their disease course. In addition, another study reported a different prognosis based on the diagnosis of MPA and levels of inflammatory markers in patients with ANCA-positive ILD. Objectives: However, it remains unknown which patients with positive ANCA results who are not initially diagnosed with AAV at the time of IIP diagnosis are more prone to the future development of systemic vasculitis. Furthermore, given the increased incidence of ILD in anti-MPO-positive patients among ANCA-positive patients, research specifically targeting patients in East Asia where MPA is more predominant is needed. Therefore, we aimed to explore the subsequent development of AAV and its risk factors in patients with positive ANCA results at the time of IIP diagnosis. Methods: We retrospectively reviewed the electronic medical records of patients with positive ANCA results at the time of diagnosis of IIP from January 2013 to December 2021 from single tertiary center in Seoul, South Korea. Cox regression analysis was performed to identify variables associated with the development of AAV among patients with IIP and positive ANCA results. Kaplan-Meier curves were used to investigate the relationship between autoantibodies and the occurrence of AAV. Results: A total of 158 patients diagnosed with IIP with positive ANCA results were included. The median patient age was 68.0 years, and 63.9% were male. Fifteen (9.5%) patients eventually developed AAV during the follow-up period after the diagnosis of IIP. The AAV group and non-AAV group did not show statistically significant differences in terms of gender, age, smoking status, and urinalysis or high-resolution computed tomography findings. The AAV group exhibited a higher body mass index (BMI) (25.9 vs. 23.8 kg/m2, p=0.018) and higher diffusing capacity (DLco) (70.7% vs. 57.4%, p=0.008) than the non-AAV group. Autoantibody analysis revealed that all patients with AAV were anti-MPO positive, while only 45.9% in the non-AAV group showed positivity (pConclusion: In our cohort, approximately 10% of patients with ANCA-positive IIP eventually developed AAV during the follow-up period after IIP diagnosis. The presence of anti-MPO or RF positivity were predictive factors associated with the subsequent occurrence of AAV. These findings underscore the importance of close monitoring and observation in patients with high-risk antibody profiles for the potential development of AAV, even in patients in whom AAV is not diagnosed at the time of the initial diagnosis of IIP. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests: None declared.