A 46-year-old woman developed takotsubo cardiomyopathy and nephrotic syndrome. The first kidney biopsy suggested non-immune-complex-mediated membranoproliferative glomerulonephritis (MPGN), and she was diagnosed with glomerular endothelial injury associated with takotsubo cardiomyopathy. A second biopsy was performed two years later because of persistent proteinuria despite renin-angiotensin system inhibition. This biopsy indicated non-immune-complex-mediated MPGN, but a mesangial and subendothelial substance of a higher electron density than that in the first biopsy was detected, suggesting the possibility of glomerular disease with non-immune deposits rather than endothelial injury. Finally, she was diagnosed with fibronectin nephropathy. Although rare, fibronectin glomerulopathy should be considered in non-immune-complex-mediated MPGN.
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