High Renal and Pulmonary Involvement and Mortality in Chinese Patients with Granulomatosis with Polyangiitis and Microscopic Polyangiitis: An Epidemiological Study in Hong Kong

Objectives: Granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA) are the two major subtypes of anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) and are associated with substantial mortality. Geographic variation exists in the epidemiology and clinical manifestations of AAV, with Southeast Asian populations showing a predominance of MPA and higher mortality. However, data on Chinese populations remain limited. This study aimed to investigate the epidemiology, mortality risk, and prognostic factors of GPA or MPA in Chinese patients in Hong Kong. Methods: Newly diagnosed cases of GPA and MPA from 2013 to 2023 were identified using ICD-9 codes from databases across eight public hospitals in Hong Kong. Incidence rates were calculated using population denominators. Patient demographics, clinical features, treatments, and outcomes, including survival, relapse, and dialysis requirement, were analyzed using the Kaplan–Meier method and Cox proportional hazards regression. Results: A total of 35 patients with GPA and 127 patients with MPA were identified. The estimated incidence rates of GPA and MPA were 0.9 and 3.2 per million population, respectively. Renal and pulmonary involvement was common, occurring in 82.1% and 51.2% of patients, respectively. Mortality rates were 22.8% at 1 year and 34.0% at 5 years. The age- and sex-adjusted standardized mortality ratio was [Formula: see text]. Multivariate analysis identified age, renal dysfunction, and pulmonary involvement as independent risk factors for mortality. Subgroup analysis showed better dialysis-free survival among patients treated with rituximab than among those treated with cyclophosphamide. Conclusions: Chinese patients with AAV presented with severe renal–pulmonary disease and markedly elevated mortality. Older age, renal dysfunction, and pulmonary involvement were associated with an increased risk of mortality. Rituximab appeared to be associated with better dialysis-free survival than cyclophosphamide.