263. Diagnosis and clinical features of respiratory involvement in ANCA-associated vasculitis

Background: Respiratory involvement is a heterogeneous clinical feature in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). This study aims to describe the frequency and characteristics of respiratory involvement in AAV and the risk factors for respiratory relapse. Methods: We conducted a retrospective study between 2004 and 2019 of all patients over 18 years in Toulouse University Hospital (France) with a diagnosis of microscopic polyangiitis (MPA) or granulomatosis with polyangiitis (GPA). We collected the clinical and paraclinical data (including biological findings, pulmonary function tests, CT imaging, endobronchial lesions and bronchoalveolar lavage fluids). We classified respiratory involvement into four groups: diffuse alveolar haemorrhage (DAH), pulmonary nodules and masses, interstitial lung diseases (ILDs) -excluding DAH- and tracheobronchial involvement. Respiratory and non-respiratory relapses were also noted. Results: Two hundred and seventy-four patients were included. One hundred fifty-one (55%) had respiratory involvement after excluding differential diagnoses (e.g. pulmonary infections, pre-existing lung diseases). DAH was the most frequent manifestation (52%), followed by nodules and masses (32%), tracheobronchial involvement (16%) and ILDs (15%). Alternative diagnoses to AAV were found in 55% of tracheobronchial presentations, 22% nodules, 16% DAH, and 15% ILDs. The coexistence of multiple lesions concerned 12% of patients. A total of 86 patients (31%) experienced a relapse within a median of 66 months. Relapse occurred more frequently in anti-PR3 patients (p=0.0007) and those who had not received rituximab as maintenance therapy (p