Dexamethasone and Chemotherapy With or Without Plasma Exchange in Patients With Newly Diagnosed Multiple Myeloma and Acute Kidney Failure

DISEASE CHARACTERISTICS: * Newly diagnosed multiple myeloma (MM), meeting ≥ 2 of the following criteria: * Serum or urine\* paraprotein * Bone marrow showing \> 10% plasma cells * Lytic bone lesions NOTE: \*The presence of typical myeloma kidney on renal biopsy is considered equivalent to the demonstration of urine paraprotein by electrophoresis * Acute renal failure attributable to MM, meeting both of the following criteria: * Creatinine \> 5.65 mg/dL OR urine output \< 400 mL/day OR requires dialysis * Unresponsive to treatment with fluids and/or treatment of hypercalcemia with bisphosphonates * No significant intrinsic renal disease unrelated to MM PATIENT CHARACTERISTICS: * Platelet count ≥ 50,000/mm³ * Bilirubin ≤ 1.5 times upper limit of normal (ULN) * ALT and AST ≤ 2.5 times ULN * No contraindications to study medication, including the following: * Active or recent peptic ulcer * Known significant cardiac insufficiency * Allergy to study medications * Not pregnant or nursing * Fertile patients must use effective contraception * No known HIV positivity PRIOR CONCURRENT THERAPY: * No prior chemotherapy for MM * Prior steroid therapy of ≤ 3 days duration for MM allowed