Unusual Casts in a Case of Multiple Myeloma

(A) Periodic acid–Schiff (PAS) and (B) silver stains show casts that are PAS and silver negative (thin arrows) and PAS and silver positive (thick arrows). PAS- and silver-positive casts represent amyloid casts, whereas PAS- and silver-negative casts represent myeloma kidney (cast nephropathy) casts (A, B: original magnification ×40). Casts (C) stain for λ light chains and (D) are negative for κ light chains.

(A, B) Trichrome, (C) PAS, and (D) silver stains show tubular casts with spicules and surrounding inflammatory cells (A, B: original magnification: A, ×10; B, D, ×40; C, ×60). (E) Congo red stains show that the casts are Congo red positive (original magnification ×60), and (F) electron microscopy confirmed the diagnosis of tubular amyloid (original magnification ×4,200).