OBJECTIVES: Severe antineutrophil cytoplasmic antibody (ANCA) associated vasculitis (AAV) is a rare disease that primarily affects the small to medium arteries. The heterogenous nature of presentation poses challenges to understanding the incidence and prevalence of severe AAV. Health resource utilisation provides an indication of the incidence of patients with severe AAV who are diagnosed and treated. One study determined a cumulative incidence of 13.4 per million and a prevalence of 134.1 per million, translating to approximately 400-500 patients treated per year, based on hospitalisation between 1995 and 2005 (Ormerod, 2008).

METHODS: Patients diagnosed with severe AAV in Australia are initially treated with one of two treatments as induction therapy, rituximab (RTX) or cyclophosphamide (CYC). Both RTX and CYC are reimbursed on the Pharmaceutical Benefits Scheme (PBS) in Australia for AAV. Rituximab was nationally reimbursed with a specific identifier for induction therapy for severe AAV between 2017 and 2022. RTX usage during this period was analysed from a 10% PBS sample. To estimate the relative use of RTX and CYC, a survey of 55 Australian and New Zealand clinicians during this period (Chua, 2023) found an approximately equal proportion of respondents would prescribe RTX or CYC as induction therapy for severe AAV. This is consistent with clinical guidelines for the period of investigation which assigned equal weighting to the choice of RTX versus CYC (Yates, 2016).

RESULTS: Extrapolation of RTX data determined a severe AAV incidence rate of 3.8 - 4.1 persons treated per 100,000. This translates to 1,024 to 1,106 unique patients treated in 2024.

CONCLUSIONS: The incidence of patients with severe AAV treated in Australia is likely to be higher than previous studies have shown.