We studied seven patients with idiopathic Bence Jones proteinuria (excretion greater than 1.0 g per 24 hours) who did not have acquired Fanconi's syndrome or an intact monoclonal immunoglobulin in the serum. None had evidence of overt multiple myeloma, of its variants, of systemic amyloidosis, or of malignant lymphoproliferative diseases when the proteinuria was recognized. In three of the seven patients, symptomatic multiple myeloma (associated with systemic amyloidosis in one) developed 8.8 to 21.1 years later. A fourth patient has asymptomatic myeloma and has not been treated. A fifth patient had an evolving myeloma at nine years but died of an unrelated cause. The remaining two patients still have apparently benign Bence Jones proteinuria after 7.7 and 12 years. Plasma-cell labeling indexes were low in all cases tested. This experience shows that although idiopathic Bence Jones proteinuria may remain stable for years, multiple myeloma or amyloidosis often develops, and consequently these patients must be kept under observation indefinitely.
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