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Diagnose This 3/18/2024

By Joel Murphy, MD

Mar 18, 2024

What is at the top of your differential in a patient with a positive SPEP (IgG kappa) and the immunofluorescence finding below? (hint: lambda is negative)

The immunofluorescence image depicts amorphous, smudgy staining with kappa light chain predominately within the mesangium while lambda light chain is completely negative. This finding by immunofluorescence taken with the clinical history is highly suspicious for renal amyloidosis, AL-type. By light microscopy, numerous vessels and glomeruli contained PAS-pale, nonargyrophilic amorphous material suspicious for amyloid deposition. A Congo red stain in this case was positive showing characteristic apple-green birefringence under polarized light within this material. Additionally, electron microscopy demonstrated numerous randomly arranged fibrils around 10 nm in diameter within the mesangium and glomerular basement membranes consistent with amyloidosis.

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