MPO and acute kidney injury: Three of the 4cases had biopsy-confirmed vasculitis in the absence of the PR-3 or MPO antibodiestypically associated with ANCA vasculitis.7,13 The fourth case had positiveMPO antibodies with biopsy-proven vasculitis.9 In this article, we discuss an 85-year-old Caucasian male who presented withacute renal failure, monoclonal IgG kappa protein, and positive MPO and PR-3serologies, and the importance of differentiating the mechanism of renal failure,which in turn would have significant implications on therapy (bortezomib for myelomakidney vs cyclophosphamide and/or rituximab for vasculitis).