Diagnose This (March 29, 2021)

What would be your leading diagnosis given the glomerular changes in a patient with an abnormal SPEP? (Hint: Congo red and DNAJB9 stains are negative, powdery deposits by EM)

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Answer: The glomerulus demonstrates nodular mesangial matrix expansion and deposition of a non-agyrophilic material on the Jones silver stain which also shows “chunky” positive staining on PAS stain. By immunofluorescence, there was diffuse, 3+ staining for kappa light chain within the glomeruli and tubular basement membranes compatible with light chain deposition disease (LCDD). By electron microscopy, the biopsy showed extensive “powdery” deposits along the tubular basement membranes, glomerular mesangium, and glomerular capillary loops characteristic of this entity.