Concomitant monoclonal immunoglobulin deposition disease and crystalglobulin-induced nephropathy with a membranoproliferative pattern of glomerular injury

Monoclonal immunoglobulin paraproteins can deposit in the kidney in variable forms and eliciting differing patterns of injury. Crystalglobulin-induced nephropathy is a rare form of monoclonal immunoglobulin deposition in the kidney, characterized by glomerular capillary endoluminal crystalline material evident by light and electron microscopy that exhibits immunoglobulin restriction via immunofluorescence studies. We present a case of a patient with acute kidney injury, and a subsequent kidney biopsy notably revealed concurrent monoclonal immunoglobulin deposition disease (MIDD) and crystalglobulin-induced nephropathy secondary to an IgM/κ monoclonal protein that resulted in a membranoproliferative pattern of glomerular injury. The two process were distinctly evident by ultrastructural crystalline and non-crystalline (as seen with cases of more conventional MIDD) deposits in the glomeruli. The paraprotein constituency is novel (IgM/κ) for crystalglobulin-induced nephropathy (prior cases exhibited IgG/κ restriction) as was the finding of the two monoclonal immunoglobulin deposition processes contributing to development of an active glomerulitis characterized by a membranoproliferative pattern of glomerular injury (crystalglobulin-induced nephropathy has not been associated with an active glomerulitis before). .