Arsalan Alvi ¹ Alexander J. Gallan ² Nattawat Klomjit ^1*

• ¹ Division of Nephrology and Hypertension, Department of Medicine, University of Minnesota, Minneapolis, Minnesota, United States
• ² Department of Pathology and Laboratory Medicine, Medical College of Wisconsin, Milwaukee, Wisconsin, United States

A toxic monoclonal protein typically results in a single kidney pathology due to specific biophysical characteristics of monoclonal proteins. Multiple monoclonal protein lesions are rarely reported and often portend poor prognosis. We present a 57-year-old male who developed rapidly progressive glomerulonephritis after concealed ruptured diverticulitis. A kidney biopsy showed light chain cast nephropathy, light chain proximal tubulopathy, and thrombotic microangiopathy. Laboratories showed IgG kappa with an M-spike of 0.2 g/dl and a kappa light chain of 16 mg/dl. A bone marrow biopsy showed 3% kappa-restricted plasma cells. The dramatic renal presentation despite the minimal hematological burden is suggestive of a highly toxic light chain, which is consistent with monoclonal gammopathy of renal significance (MGRS). Clone-directed therapy and a complement blockade were initiated. The patient remained dialysis-dependent despite a hematological response. This case highlights the importance of toxic properties of monoclonal protein in causing kidney diseases. Our case is the first report of an MGRS patient with three distinct kidney lesions. Triple monoclonal protein related kidney lesions are very rare and are usually associated with multiple myeloma. LCCN is a myeloma defining event but his LC (<50 mg/dl) and plasma cell burden was low (<10%) which makes this case very unusual. Sepsis-induced low flow stage and toxic properties of LC may induce LCCN in this patient. Aggressive therapy is likely needed to eradicate the clone in order to achieve an organ response.