MPO and polyarteritis nodosa: Most cases of VM develop in the setting of polyarteritis nodosa (PAN), myeloperoxidase-specific antineutrophil cytoplasmic antibody (MPO-ANCA)-associated vasculitis (AAV), rheumatoid vasculitis, or manifest as single organ vasculitis that predominantly affects medium- or small-sized arteries, respectively [9, 27, 39, 47, 62].