What is your diagnosis?

 

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This photomicrograph shows extensive, granular, PAS-positive material within the interstitium and tubular basement membranes and is consistent with light chain type deposits. Light chain deposition disease is typically thought of as a disease affecting the glomeruli and tubular basement membranes, however, some cases can show extensive light chain deposits that spill into the vasculature and interstitium as seen here. In this case, lambda light chain restriction was seen in these deposits and they were Congo red negative (not shown). By electron microscopy, punctate, powdery light chain type deposits were seen frequently (see photo below).