These patterns have important diagnostic value: proteinase 3-ANCA is most commonly associated with GPA, while MPO-ANCA is more frequently observed in MPA and EGPA.[1] This disease can occur at any age and affects all races.[2,3] Recent studies report prevalence rates of 300 to 421 per million people.[4,5] AAV can affect multiple organ systems, with a wide range of clinical manifestations. Here, MPO is linked to microscopic polyangiitis.