Diagnose This (March 26, 2018)

In the setting of weak C3 (1-2+) only staining by routine immunofluorescence, what is your diagnosis?

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These photomicrographs show a membranous pattern glomerulopathy with C3 staining by immunofluorescence. While it is tempting to diagnosis this as C3 glomerulopathy, that is not correct in this case. Further studies for paraffin immunofluorescence were performed and showed intense IgG, C3 and kappa staining within deposits confirming a Membranous-Like Glomerulopathy with Masked IgG Kappa Deposits (see reference). Membranous-Like glomerulopathy with Masked IgG Kappa Deposits is a relatively new diagnostic category that typically affects young females, often displaying vague autoimmune symptomatology, and can easily be mistaken for C3 glomerulopathy due to its masked staining qualities on routine paraffin immunofluorescence. Because of this and other masked lesions (such as some cryoglobulinemic GNs and paraprotein-related GNs) predilection for staining with C3 only by routine immunofluorescence, we suggest paraffin retrieved immunofluorescence be done on all C3 only staining cases before a diagnosis of C3 glomerulopathy is rendered.

Reference Link: https://www.ncbi.nlm.nih.gov/pubmed/24429395