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Bone marrow biopsy Renal biopsy

* Frequency of renal involvement.

* Frequency of renal involvement.

FIGURE 5-22 (see Color Plate)

A, Paraprotein abnormalities as a cause of nephrotic syndrome. This table compares the characteristics of various paraproteinemias. Paraproteins are abnormal immunoglobulins or abnormal immunoglobulin fragments produced by B lymphocytes. They are monoclonal, appear in the serum or urine (or both), and cause renal damage by several different mechanisms. Paraproteinemias comprise a group of disorders characterized by overproduction of different paraproteins.

Multiple myeloma is a common type of paraproteinemia. The overproduction of immunoglobulins or light chains, or both, causes renal toxicity, directly affecting the tubular cells or forming casts after precipitation in the tubular lumen. The light chains may be transformed into amyloid fibrils and deposited in various tissues, including the kidney. Amyloidosis is diagnosed by performing a biopsy of the involved organ and staining the tissue with Congo red stain. On occasion, the light chains do not form fibrils but are deposited as granules along the basement membrane of blood vessels and glomeruli. Kappa chains often behave in this manner. This entity is called light-chain deposition disease [6] (panel B).

Paraproteins composed of IgM are noted in Waldenstrom's macroglobulinemia. Renal dysfunction is uncommon in this condition [49]. Hyperviscosity is present. On rare occasions, thrombi composed of IgM may be noted in the glomeruli of these patients.

In the most common form of paraproteinemia, monoclonal protein is detected in the serum of an otherwise healthy person. This condition is referred to as monoclonal gammopathy of unknown significance (MGUS) and may on occasion progress to multiple myeloma or amyloidosis [50].

B, Light-chain deposition disease (LCDD) in a patient with multiple myeloma. A light microscopic study of a renal biopsy specimen from a 65-year-old man with recently diagnosed multiple myeloma who was found to have an elevated serum creatinine concentration (2.6 mg/dL) and proteinuria of 3 g/d. Note the nodular mesangial lesions, capillary wall thickening, and hypercellularity resembling diabetic nodular glomerulosclerosis. Immunofluorescence staining was positive for kappa light chains but negative for lambda light chains.

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