What is your leading diagnosis when seeing this particular IgG staining pattern?
Answer: Fibrillary Glomerulopathy
The immunofluorescence shows a glomerulus with a characteristic “smudgy” pattern of staining with IgG within the mesangium with segmental extension into the capillary loops characteristic of Fibrillary Glomerulopathy. Fibrillary GN is an extremely rare disease, seen in <1% of native kidney biopsies and is caused by the deposition of fibrillar deposits which are characterized as non-branching, randomly arranged, and have an average diameter of approximately 20 nm (range: 10-30 nm).
In addition to identifying fibrils by electron microscopy, an immunohistochemical stain DNAJB9, is typically positive as it shows a 98% sensitivity and greater than 99% specificity in these cases. Approximately 40-50% of all patients will progress to ESRD within four years and the disease carries a high recurrence rate within renal allografts (up to 50%). Approximately 17% of patients with Fibrillary GN had a concomitant positive SPEP/UPEP, necessitating the need to further rule out a dysproteinemia in these patients.
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