In a patient with renal dysfunction and proteinuria, myeloma is part of the differential diagnosis. However, in myeloma, even though the majority of protein in the urine may be albumin (owing to tubular damage caused by light chains), one would expect to see some light chains. In this patient who has no light chains in the urine and only a small monoclonal serum protein spike, the chance of finding myeloma is very small and, in these clinical circumstances, one might have chosen not to do a marrow examination. The diagnosis of myeloma requires finding plasma cells occupying one half of a high power field. While this extent of marrow involvement can occur with only moderate elevations of serum immunoglobulins, IgG levels of greater than 3000 mg/dL or IgA levels greater than 2000 mg/dL often are seen at the time of diagnosis in patients with myeloma. Neither of these criteria is met in this case. Despite the presence of anemia, renal dysfunction, and a monoclonal protein, the working diagnosis is not myeloma but MGUS.
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