MPO and vasculitis: There are four distinct MPO and proteinase 3 (PR3) double-positive ANCA angiitis types: idiopathic, drug-induced, autoimmune, and immune-disrupting types not associated with ANCA-associated vasculitis (AAV) [5]. Based on a study of over one hundred double-positive ANCA confirmed cases, there is a significant variation in terms of clinical and immunopathological manifestations; approximately half of the patients have developed AAV [5].