The two most common morphologic variants of light chain proximal tubulopathy (LCPT) are LCPT with and without crystal formation. The histopathologic lesions of light chain proximal tubulopathy with crystal formation are shown here. (A) A case with dense crystal deposition resulting in a focally pale appearance to proximal tubules on periodic acid-Schiff stain (original magnification × 100). (B) Crystals are easily identified due to dark staining on Toluidine blue stain (original magnification × 400). (C) A light chain crystal (arrow) stains brightly fuchsinophilic on Masson trichrome stain in this case with rare crystal deposition (original magnification × 400). (D-F) Crystals can take on a variety of ultrastructural morphologies including (D) rhomboid shaped (original magnification × 8000), (E) rod-shaped (original magnification × 15,000), and (F) rounded (original magnification × 5000).
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