κ light chain — myeloma associated with adult Fanconi syndrome: Response of the nephropathy to treatment of myeloma

The association of Bence Jones proteinuria with adult Fanconi syndrome has been reported in a small number of patients. The nephropathy and the Bence Jones proteinuria often precede by several years the diagnosis of frank myeloma. A 39-year-old woman developed renal glucosuria 2.5 years prior to the diagnosis of a plasma cell disease characterized by k Bence Jones proteinuria, osteolytic lesions, and histologically proven plasmacytomas. Serum phosphorus of 1.1–2.1 mg/dl and uric acid of 1.3–1.6 mg/dl were compatible with Fanconi syndrome. Glucosuria was constantly present, while the glucose tolerance test was normal. Urinary β2 microglobulin (β2M) excretion was up to 135 mg/24 hours (normal less than 0.14 mg), indicating failure of tubular absorption of this protein. Amino-aciduria was noted. The patient's myeloma responded to irradiation followed by melphalan plus prednisone and vincristine; the result was a marked reduction of the Bence Jones proteinuria. Some of the manifestations of the Fanconi syndrome disappeared, while the others were markedly reduced; this included disappearance of the glucosuria, elevation of the serum phosphorus and uric acid to normal, decrease of the urinary amino acid excretion to the normal range in 11 of the 14 amino acids tested, and decrease in the β2 M excretion to 5.4 mg/24 hours. The response of the Fanconi syndrome to the treatment of myeloma supports the view that the nephropathy is due to the myeloma process, probably through renal tubular injury induced by Bence Jones proteinuria.