MPO and Chronic tubulointerstitial nephritis: Prior biopsy reviews of 118 patients with MM by Montseny et al haverevealed myeloma kidney in 48% of patients, AL amyloidosis in 30%, light chaindeposit disease in 19%, chronic tubulointerstitial nephritis in 10%, andcryoglobulins in <1%.14 The positive PR-3 and MPO antibodies present in our case raised concern forvasculitis as an alternative etiology for renal dysfunction.