Society of Diabetic Nephropathy Prevention Journal of Nephropathology 2251-8363 10 1 2021 01 01 Lambda light chain crystalline proximal tubulopathy with probable light chain cast nephropathy and clonal plasma cell infiltrate – uncommon manifestations of a rare form of multiple myeloma e08 e08 10.34172/jnp.2021.08 EN Yan-Fei Ng https://orcid.org/0000-0003-1213-9280 Chang-Yin Choinh https://orcid.org/0000-0003-2809-8321 Marvin Raden Torres De Guzman https://orcid.org/0000-0002-8034-3884 Chandramouli Nagarajan https://orcid.org/0000-0001-5755-2226 Hwai-Liang Loh https://orcid.org/0000-0003-3852-040X Journal Article 10.34172/jnp.2021.08 2020 01 10 2020 04 24 Light chain proximal tubulopathy (LCPT) is an uncommon renal disease characterized by the accumulation of monoclonal light chains within proximal tubular epithelial cells, with or without crystal formation. We report a rare case of lambda LCPT with crystals. Renal biopsy showed substantial acute tubular injury with unusual cytoplasmic changes affecting proximal tubules. In addition, abnormal tubular casts suggested concomitant light chain cast nephropathy. A clonal plasma cell infiltrate was present in the tubulointerstitial compartment. Immunofluorescence demonstrated strong staining for lambda light chain in tubular epithelial cells. Despite the absence of discernible crystals on light microscopy (LM), they were readily identified when ultrastructural evaluation was undertaken. Crystalline inclusions demonstrated positive immunogold labelling for lambda.