Case Report Reversible Fanconi syndrome due to lenalidomide

Renal disease is a common manifestation of multiple myeloma (MM), a plasma cell dyscrasia. The spectrum of renal disease includes cast nephropathy, light chain amy-loidosis, monoclonal Ig deposition disease and cryoglob-ulinemic as well as proliferative glomerulonephritis. Pa-tients most often present with abnormal renal function and proteinuria. Occasionally, patients also present with renal tubular dysfunction such as acidification and concentra-tion defects and rarely with Fanconi syndrome (FS) [1]. FS is a proximal renal tubular dysfunction characterized by renal glucosuria, generalized aminoaciduria and hypophos-phatemia. Othermanifestationsmay include defect of bicar-bonate reabsorption, renal acidification, urinary concentra-tion, potassium as well as sodium and calcium reabsorption [2]. Kidney biopsy in patients with FS due toMMmay reveal cytoplasmic crystals in proximal tubule cells or tubulointer-stitial nephritis without glomerular lesion. The immunoflu-orescent studies reveal that the crystals stain strongly for monoclonal light chains. The majority of MM patients who develop FS have κ light chain disease [3]. Besides MM, a multitude of medications and toxins have been reported to cause acquired FS [2]. Lenalidomide is a novel antineoplastic agent active against MM through a variety of mechanisms including inhibition of angiogenesis, induction of apoptosis, im-munomodulation, antiproliferative effects, inhibition of the cytokine signaling and stimulation of T-cell activity. The major side effects of this agent include myelosuppression and thromboembolic events. Hypokalemia and hypocal-cemia are rare side effects of lenalidomide [4,5]. We report a patient with refractory IgG λ MM treated with lenalidomide who developed FS