| Summary: | Kidney amyloidosis typically presents with nephrotic-range proteinuria. Rare cases of crescentic glomerulonephritis have been reported in patients with kidney amyloidosis but most cases were in the setting of patients with AA amyloidosis from long-standing inflammation and malignancy. We present a case of a previously healthy man in his 70s who was admitted with severe acute kidney injury, nephrotic-range proteinuria, and nephritic urinary sediment. Initial serologic testing for causes of rapidly progressive glomerulonephritis were negative. Kidney biopsy demonstrated the presence of active cellular and fibrocellular crescents with Congo red–positive staining in glomeruli and microvasculature on light microscopy and amyloid fibrils in glomerular basement membrane on electron microscopy. Urinary protein electrophoresis revealed monoclonal λ light chains, leading to a diagnosis of kidney AL amyloidosis, which was confirmed with bone marrow biopsy. Our case illustrates that AL amyloidosis can present with findings suspicious for rapidly progressive glomerulonephritis and crescent formation on kidney biopsy specimens.
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