Light Chain Crystalline Proximal Tubulopathy and Podocytopathy With Staining for Both Light and Heavy Chain Immunoglobulin

ABSTRACT A 69‐year‐old male patient presented with weight loss and proteinuria. His medical history included papillary thyroid carcinoma. Laboratory findings showed proteinuria and high κ light chain levels in both urine and serum. Bone marrow aspiration revealed plasma cell myeloma of the IgA‐ κ type. Kidney biopsy revealed crystal inclusions in multiple locations, including podocytes and proximal tubular epithelial cells. Immunofluorescence and immunohistochemistry revealed positive staining for κ light chain and IgA. The patient was diagnosed with light chain crystalline podocytopathy and proximal tubulopathy. Our case presented some peculiarities: positive staining for heavy‐chain IgA in addition to κ light chain and the absence of concurrent Fanconi syndrome or focal segmental glomerulosclerosis.