Acquired fanconi syndrome with osteomalacia secondary to monoclonal gammopathy of undetermined significance.

A 60-year-old woman was admitted because of multiple bone pain. Examination revealed hypophosphatemic osteomalacia and acquired Fanconi syndrome. Further exploration revealed monoclonal gammopathy of undetermined significance (MGUS) excreting urinary Bence Jones protein (kappa light chain). Renal biopsy showed non-specific tubulointerstitial nephritis, yet neither crystalline inclusions in the cytoplasm of the tubular epithelium nor myeloma casts nor amyloid deposits were found. She was treated with supplementation by phosphate, alkali agents, and vitamin D, and responded well to the treatment symptomatically and biochemically. MGUS was observed without chemotherapy. Myeloma had not developed after 10 months follow-up.