Diagnose This (November 23, 2020)

Based on the image provided, what would be your leading diagnosis with C3-dominant immune-complex deposition?

    ​ ​   ​   ​ ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​   ​ ​   ​ ​   ​ ​   ​ ​     ​

Answer: The light microscopic image depicts a glomerulus with a diffuse proliferative and exudative pattern of injury characterized by neutrophilic endocapillary hypercellularity. In addition, other glomeruli showed cellular crescent formation with associated fibrinoid necrosis. These glomerular findings in association with C3-dominant immune-complex deposition by immunofluorescence are concerning for an underlying infection. Of note, necrotizing and crescentic GN was the most common histologic pattern of injury seen in a case series by Boils et al. In their series, the most common organisms encountered were S. aureus and Streptococcal species which most commonly affected the tricuspid valve. In this series, close to 1/3 of patients also had a positive ANCA antibody.

Boils CL, et al. Update on endocarditis-associated glomerulonephritis. Kidney International (2015) 87, 1241–1249.