What is cast nephropathy?
The most common histologic finding in myeloma is cast nephropathy (MCN), which is characterized by eosinophilic acellular fractured casts, with brittle cracks commonly in the distal tubules and collecting ducts, and—to a lesser extent—in the proximal tubules with epithelial cell necrosis and thinning and dilatation of the lumina. The casts are surrounded by inflammatory cells including macrophages, multinucleated giant cells, and polymorphonuclear neutrophils. There is interstitial edema and inflammation, and in the later stages interstitial fibrosis ( Fig. 39.1 ). The casts usually stain for a monoclonal LC. In some cases, casts are absent but the interstitial inflammation and fibrosis are present.
