Myeloma cast: Light microscopy

High-power light micrograph shows PAS stain of tubular casts in myeloma kidney. The bottom two tubules contain casts composed of PAS-negative immunoglobulin light chains (small arrows). By comparison, the cast in the middle tubule (probably hyaline) is primarily composed of PAS-positive Tamm-Horsfall mucoprotein, the matrix of all casts (large arrow). Myeloma proteins are PAS negative because they contain few of the neutral sugars that are detected by this stain.