Figure 6.

κ–LCPT, crystalline type. Several different examples of light-chain proximal tubulopathy are illustrated. (A) A case with abundant trichrome clear or weakly red intracellular crystals that distort the cytoplasm of proximal tubular epithelial cells throughout the biopsy (Masson trichrome). Original magnification, ×400. (B) Although the initial immunofluorescence stain for κ-light chain performed on frozen sections was negative (not shown), repeat immunofluorescence on pronase-digested paraffin sections is brightly positive for κ-light chain only in the distribution of the intracellular needle-shaped crystals. There was negativity for λ-light chain (not shown). Original magnification, ×400. (C) By electron microscopy, the proximal tubular cells are engorged with rhomboidal crystals throughout the full thickness of their cytoplasm. The proximal epithelial cells show acute injury with loss of brush border and shedding of cytoplasmic fragments and degenerating cellular debris into the lumen. Original magnification, ×5000. (D) An example with hexagonal trichrome red crystals irregularly distributed within the proximal tubular cell cytoplasm. The tubular epithelial cells exhibit acute injury but no intraluminal casts (Masson trichrome). Original magnification, ×400. (E) A case with large crystalline inclusions staining by immunofluorescence for κ-light chain only within the cytoplasm of proximal tubular cells was revealed following antigen retrieval by application of pronase digestion to paraffin sections. Original magnification, ×400. (F) High-power view of a representative proximal tubular cell from the same patient as in C above shows rhomboidal and other geometric-shaped crystals with lateral striations, indicating periodicity. The crystals are located within membrane-bound phagolyosomes or free within the cytosol of proximal tubular cells (electron micrograph). Original magnification, ×30,000.