Plasma cell myeloma is a malignancy of plasma cells (see Chapter 13) that can cause a variety of kidney disorders. Injury is due to the toxic effects of monoclonal immunoglobulins or light chain components produced by plasma cells. Cast nephropathy (formally called “myeloma kidney”) is the most common kidney disease in plasma cell myeloma and occurs when light chains (Bence Jones protein) overwhelm the reabsorptive capacity of the tubules, leading to precipitation in the distal nephron and tubular obstruction. Plasma cell myeloma may also cause Fanconi syndrome, a type 2 (proximal) renal tubular acidosis characterized by hypophosphatemia and inappropriate glycosuria. Proteinuria in cast nephropathy is exclusively tubular; hence, urine dipstick findings are minimal since glomerular proteinuria is not present. Hypercalcemia and hyperuricemia are frequently seen. Another kidney disorder in patients with plasma cell myeloma is glomerular amyloidosis with nephrotic syndrome; in these patients, urine dipstick is positive due to glomerular epithelial cell foot-process effacement and albumin “spilling” into the Bowman capsule; hematuria may or may not be present. Other conditions resulting in kidney disease include plasma cell infiltration of the renal parenchyma and hyperviscosity syndrome compromising renal blood flow. The presence of myeloma-related kidney disease does not itself preclude use of contrast dye for imaging studies; standard precautions for the use of intravenous contrast and gadolinium in patients with reduced GFR apply to patients with myeloma-related kidney disease. Therapy for AKI (see Acute Kidney Injury, above) attributed to plasma cell myeloma includes correction of hypercalcemia; volume repletion; and chemotherapy for the underlying malignancy, typically with bortezomib-based agents. Plasmapheresis and high cutoff hemodialysis are sometimes considered to reduce the burden of circulating free light chains, but results have been equivocal and their use is controversial. Additionally, high cutoff hemodialysis is not available in many countries, including the United States.
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