Pauci-immune Crescentic Glomerulonephritis Due to MGRS Crystalline Nephropathy

There are several known mechanisms by which monoclonal Igs (MIg) or their subunits can cause kidney disease: (i) deposition in 1 or more kidney compartments, resulting in distinct clinicopathologic lesions, such as Ig-related amyloidosis, monoclonal Ig deposition disease, and a variety of glomerulonephritides, including cryoglobulinemic glomerulonephritis type I and II, immunotactoid glomerulonephritis, and proliferative glomerulonephritis with monoclonal immunoglobulin deposits; (ii) precipitation in tubular lumina (e.g., myeloma cast nephropathy); (iii) activation of the alternative pathway of complement (e.g., C3 glomerulopathy associated with monoclonal gammopathy, thrombotic microangiopathy associated with monoclonal gammopathy); (iv) cytokine activation (e.g., POEMS syndrome); and (v) crystallization in the renal vasculature (e.g., crystalglobulin-induced nephropathy).1, 2 Here, we describe an unusual case of monoclonal gammopathy of renal significance (MGRS)–associated crystalline nephropathy that does not conform to any of the previously described patterns of kidney involvement by monoclonal gammopathy.