Light chain proximal tubulopathy is a rare M-proteinemia-related nephropathy. The inclusions, composed of light chains in light chain proximal tubulopathy, are generally crystalline, and most exhibit a rhombic shape. Noncrystalline structures, such as rods or needle shapes, may also be present. In our patient, one of the noncrystalline structures, fibrillary inclusions in the cytoplasm, were observed, as previously reported in only 4 patients whose primary disease was either
multiple myeloma or
monoclonal gammopathy of renal significance. This is the first report involving
lymphoma. Early diagnosis of light chain proximal tubulopathy is important because those who undergo
chemotherapy have an improved kidney prognosis. However, in cases of kidney involvement with blood disorders,
thrombocytopenia is often present. Therefore, in our case, open kidney biopsy was selected. Noncrystalline light chain proximal tubulopathy is believed to be less likely to cause
Fanconi syndrome. However,
Fanconi syndrome was observed in 3 of the 4 patients with fibrillary inclusions. In our case, hypouricemia was improved by
chemotherapy, suggesting that the patient presented with
Fanconi syndrome. Noncrystalline light chain proximal tubulopathy with fibrillary inclusions may cause
Fanconi syndrome, similar to crystalline light chain proximal tubulopathy. We report a case of light chain proximal tubulopathy with fibrillary inclusions complicated by low-grade
B-cell lymphoma in which early treatment was successful.