Multiple myeloma is a plasma cell neoplasm commonly associated with lytic bone lesions, hypercalcemia, renal failure, and acquired immune abnormalities. Clinical Features. The clinical features of multiple myeloma stem from (1) the effects of plasma cell growth in tissues, paicularly the bones (2) the production of excessive Igs, which often have abnormal physicochemical propeies; and (3)The suppression of normal humoral immunity. Bone resorption often leads to pathologic fractures and chronic pain. The attendant hypercalcemia can give rise to neurologic manifestations, such as confusion, weakness, lethargy, constipation, and polyuria, and contributes to renal dysfunction. Decreased production of normal Igs sets the stage for recurrent bacterial infections. Cellular immunity is relatively unaffected. Of great significance is renal insufficiency, which trails only infections as a cause of death. The pathogenesis of renal failure (Chapter 20), which occurs in up to 50% of patients, is multifactorial. However, the single most impoant factor seems to be Bence-Jones proteinuria, as the excreted light chains are toxic to renal tubular epithelial cells. Ceain light chains (paicularly those of the l6 and l3 families) are prone to cause amyloidosis of the AL type, which can exacerbate renal dysfunction and deposit in other tissues as well.