MPO and monoclonal gammopathy: Patients with AAV exhibit higher proportions of B lymphocytes and plasma cells than healthy controls.[16,17] Other studies have shown that rheumatologic diseases like AAV affect the risk of MM or other lymphoproliferative disorders progressed from monoclonal gammopathy of undetermined significance (MGUS).[18] In another cohort of 16 individual case studies, all patients were positive for anti-PR3 and anti-MPO antibodies and were diagnosed with MM.