[A case of renal Fanconi syndrome due to Bence Jones' protein K-type multiple myeloma]

A 60-year-old man, who had been treated for chronic kidney disease and chronic hepatitis B infection, was referred to our hospital following presentation with thoracic bone pain and exacerbation of proteinuria and hematu- ria. On admission, laboratory test results showed evidence of hypophosphatemia, glucosuria and elevated levels of both urinary NAG and 62MG.The patient was diagnosed with Fanconi syndrome based on findings indicating the presence of pan-aminoaciduria, elevated urinary excretion of uric acid and an increased phosphorus reabsorption rate. Furthermore, bone scintigraphy showed increased multiple symmetric uptake of radiotracer in both sides of the ribs, leading to the diagnosis"of hypoposphatemia-related osteomalacia with renal Fanconi syndrome. Urinary immunoelectrophoresis indicated the presence of K Bence Jones' protein (BJP). A bone marrow biopsy examina- tion showed that the plasma-to-cell ratio was less than 10%. However, the patient had over lg/day of proteinuria and suppression of serum IgM (18mg/dL) and was, therefore, diagnosed with multiple myeloma based on SWOG criteria. Light microscopic examination showed evidence of glomerulosclerosis, intimal thickness of interlobular arteries and acidophilic granular deposits in the cytoplasm of the proximal epithelial tubular cells. Immunofluores- cence indicated positive anti-K staining in these regions. Electron microscopic examination of the proximal tubular epithelial cells revealed the presence of numerous diamond-shaped and oval crystals, thought to be the K light chain of BJP. In general, cast nephropathy, light chain deposition disease (LCDD) and AL amyloidosis are recog- nized renal injuries caused by myeloma. However, there have been few clinical reports of Fanconi syndrome with multiple myeloma, such as the case study we have described here. In addition, histological examination of a biopsy sample provided further evidence of K BJP in the proximal epithelial tubular cells.