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Abstract: PO1907

A Unique Case of Light Chain Proximal Tubulopathy

Session Information

Category: Onco-Nephrology

  • 1500 Onco-Nephrology

Authors

  • Tobin, Trevor Wesley, Walter Reed National Military Medical Center, Bethesda, Maryland, United States
  • Childs, John M., Walter Reed National Military Medical Center, Bethesda, Maryland, United States
  • Yuan, Christina M., Walter Reed National Military Medical Center, Bethesda, Maryland, United States
Introduction

Light chain proximal tubulopathy (LCPT), a rare form of monoclonal gammopathy of renal significance (MGRS), is characterized by the accumulation of monotypic light chains within proximal tubular cells. LCPT may present in multiple ways, including acute kidney injury, chronic kidney disease (CKD), Fanconi’s syndrome, and proteinuria. We present a case of LCPT, presenting with CKD and non-nephrotic range proteinuria (NNRP).

Case Description

A 62 year old Caucasian male with a past medical history of IgM kappa light chain monoclonal gammopathy of undetermined significance (MGUS) presented for evaluation of CKD. Serum creatinine at the time of initial presentation was 1.4 mg%, which correlated with an estimated GFR of 54. No other electrolyte derangements were present. Urinalysis was negative for glycosuria, pyuria, or hematuria with unremarkable urine microscopy. He had NNRP on spot quantification of approximately 400 mg/g creatinine and 32 mg/g of this proteinuria was albuminuria. There was no history of hypertension or diabetes, and he denied NSAID use. He was taking no medications felt to cause chronic interstitial nephritis. Renal ultrasound was unremarkable, and 24 hour ambulatory blood pressure monitoring documented normal BP levels, on no medications. At follow up, the patient’s creatinine fluctuated between 1.4-1.6 mg%, and his proteinuria between 400-600 mg/g creatinine. Renal biopsy was pursued because there was no apparent cause to explain his CKD. Biopsy revealed numerous kappa light chain crystalline structures within proximal tubular epithelial cells by immunofluorescence staining of paraffin sections, after pronase-digestion. There was no other evidence of multiple myeloma or Waldenstrom’s macroglobulinemia on prior bone marrow biopsy. He subsequently began therapy with bendamustine and rituximab.

Discussion

We present a case of LCPT manifesting as CKD G3a A1-2. The case was indolent in nature, but was confirmed on renal biopsy using paraffin digestion to prove monoclonality of the crystalline deposits. This led to the diagnosis of a MGRS, and necessitated initiation of chemotherapeutic agents. LCPT is a rare manifestation of MGRS, and might not have been recognized in this case if suspicion had not been high, and biopsy had not been pursued.