Diagnose This (May 3, 2021)
This image is from a biopsy of a young female who presented with proteinuria during pregnancy. Routine immunofluorescence was negative. What is this stain and what is your diagnosis?
The stain depicted is Serum Amyloid Protein (SAP) immunofluorescence. SAP has been recently described as a marker that colocalizes with IgG in cases of membranous-like glomerulopathy with masked IgG kappa deposits. This entity typically presents in young females, many of which have positive autoimmune serologies but no well-defined autoimmune disease. Although the deposits are monotypic (usually IgG1 kappa), the majority of patients do not have a detectable monoclonal paraprotein, and so far no cases associated with hematologic malignancy have been described.
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