Proliferative C4 dense deposit disease, acute thrombotic microangiopathy, a monoclonal gammopathy, and acute kidney failure

Dense deposit disease (DDD) is a rare form of glomerulonephritis that has recently been reclassified under the broad group of C3 glomerulopathy, which also includes C3 glomerulonephritis. C3 glomerulopathy is characterized by predominant C3 staining on immunofluorescence microscopy and dysregulation of the alternative complement pathway. We present a case of DDD concurrent with acute thrombotic microangiopathy (TMA) in a 54-year-old white man. The patient presented with acute kidney injury, and a kidney biopsy showed segmental highly electron-dense intramembranous deposits and large rounded mesangial electron-dense deposits consistent with DDD and coexisting glomerular and vascular thrombosis consistent with concurrent acute TMA. However, immunofluorescence microscopy did not show C3 staining in nonsclerotic glomeruli, excluding C3 DDD. Rather, there was dense staining for C4d along the glomerular capillaries, suggesting C4 DDD. Activity of the alternative complement pathway was normal. To our knowledge, this is the first reported case of C4 DDD concurrent with TMA. One previous case report of C4 DDD had been reported, though in a teenage girl. These 2 cases suggest that C4 DDD is a rare entity and should be distinguished from the C3 glomerulopathies.