The patient is a 30-year-old female who presents with nephrotic range proteinuria and a creatinine of 2.5. She has a history of hypertension and joint pains. Serologies for ANA, dsDNA, and ANCA are negative.

What is the best diagnosis?

A. ANCA-associated Glomerulonephritis
B. C3 Glomerulonephritis
C. Membranous-like Glomerulopathy with Masked IgG Kappa Deposits
D. Proliferative Glomerulonephritis with Monoclonal IgG Kappa Deposits

The best answer is C: Membranous-like Glomerulopathy with Masked IgG Kappa Deposits.
An ANCA-associated glomerulonephritis is a possibility with the fibrous crescent and weak direct immunofluorescence staining. However, the ANCA is negative and the immunofluorescence stains are “unmasked” on the paraffin-embedded tissue. C3 glomerulonephritis is sometimes misdiagnosed in cases of membranous-like glomerulopathy with masked IgG kappa deposits because the paraffin tissue is not tested to look for “masked” deposits. Proliferative glomerulonephritis with monoclonal IgG kappa deposits refers to a glomerulonephritis which stains for IgG, C3, and kappa by direct immunofluorescence. In this case, the IgG and kappa were only “unmasked” on the paraffin-embedded tissue. For further reading, please follow this link https://www.ncbi.nlm.nih.gov/pubmed/24429395