Immunofluorescence shows C3 (2-3+), IgM (1+), kappa (trace) and lambda (trace).

What is your diagnosis?

 

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The image shows a glomerulus with a fibrocellular crescent dissecting portions of the glomerular tuft. Within the uninvolved portions of the glomerulus no obvious endocapillary proliferation is present and has the classic appearance of an ANCA-mediated glomerulonephritis. However, the immunofluorescence profile is unusual showing significant C3 deposition but pauci-immune heavy and light chains. Overall, these findings are most suggestive of endocarditis-associated glomerulonephritis. Endocarditis-associated glomerulonephritis displays a spectrum of light and immunofluorescence findings but can be troublesome as a mimic for ANCA-mediated glomerulonephritis and should be considered when atypical findings present in what appears by light microscopy to be ANCA-mediated glomerulonephritis. In Boils CL, Nasr SH et al study (see reference), most patients with endocarditis-associated glomerulonephritis showed reduced serum C3 levels, ≥2+ staining for at least 1 immune reactant, negative MPO and PR3 (significant minority are ANCA+ however), IV drug abuse/HCV positive, or a prosthetic valve. In our patient presented here, there was a history of prosthetic valve, reduced serum C3, and she was found to have endocarditis after kidney biopsy via trans-esophageal echocardiogram.

Reference: Boils CL, Nasr SH, et al. Update on endocarditis-associated glomerulonephritis. Kidney Int 2015 Jun;87(6):1241-9. https://www.ncbi.nlm.nih.gov/pubmed/25607109