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The term 'benign monoclonal gammopathy' indicates the presence of a monoclonal protein in persons without evidence of multiple myeloma, macroglobulinaemia, amyloidosis, lymphoproliferative disease, or other related disorders. The term 'monoclonal gammopathy of undetermined significance' (MGUS) is preferable because it is not known at diagnosis whether an M-protein will remain stable and benign or develop into symptomatic multiple myeloma or related disorders. Immunoelectrophoresis and immunofixation of the serum and urine are necessary to determine the presence and type of M-protein. At the Mayo Clinic, follow-up data have been gathered for more than 13 years on 241 patients with an initial benign monoclonal gammopathy. Nineteen per cent of these patients developed multiple myeloma, macroglobulinaemia, amyloidosis, or related diseases during the follow-up period. There is no reliable technique for differentiating a patient with a benign monoclonal gammopathy from one who will subsequently develop a serious disease. It is necessary to follow these patients indefinitely. Important in the complete understanding of the elderly patient with monoclonal gammopathy are the following: clinical manifestations, laboratory findings, and differential diagnosis of multiple myeloma; the course and prognosis and the induction therapy and treatment of multiple myeloma; newer therapeutic approaches; and the management of complications such as hypercalcaemia, hyperuricaemia, renal failure, bacterial infections, skeletal disease, and neurological problems.

This study evaluated the utility of the immunoperoxidase method as applied to bone marrow sections in the diagnosis of patients with monoclonal gammopathies. Intracellular immunoglobulin light chains were identified in fixed, decalcified bone marrow biopsy sections from 66 patients with monoclonal proteins, using an avidin-biotin-peroxidase complex immunoperoxidase method. In all cases the predominant light chain identified in the bone marrow biopsy correlated with the monoclonal light chain identified in the serum. In addition, a light chain ratio was defined that correlated with the clinical diagnoses. The light chain ratios were highest in patients with multiple myeloma and were significantly different from those with monoclonal gammopathy of undetermined significance. There was no correlation between level of serum monoclonal protein and light chain ratios. The ratios were also high in patients with macroglobulinemia, primary amyloidosis, and renal disease secondary to monoclonal proteins but without overt myeloma. Determination of light chain ratios differentiated patients with multiple myeloma from those with monoclonal gammopathy of undetermined significance and helped identify patients with end organ damage secondary to monoclonal proteins but without overt myeloma.