Abstract: FR-PO1237
When Renal Tubular Acidosis Is More Than RTA: Hypokalemic Acidosis Revealing Crystalline Light-Chain Proximal Tubulopathy
Session Information
- Onconephrology: Diagnostic Dilemmas, Therapy-Related Toxicities, and Clinical Cases
October 23, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Onconephrology
- 1600 Onconephrology
Authors
- Lee, Ruth Diana, Cleveland Clinic, Cleveland, Ohio, United States
- Dweik, Loai, Cleveland Clinic, Cleveland, Ohio, United States
- Huang, Yuan, Cleveland Clinic, Cleveland, Ohio, United States
- Mehdi, Ali, Cleveland Clinic, Cleveland, Ohio, United States
Introduction
Monoclonal gammopathy of renal significance (MGRS) can present with diverse phenotypes, including AKI, nephrotic syndrome, progressive CKD, or tubular dysfunction. Crystalline light chain proximal tubulopathy (LCPT) is a rare entity that can be difficult to diagnose. We report a case of LCPT presenting as renal tubular acidosis (RTA), initially misdiagnosed as acute interstitial nephritis (AIN).
Case Description
59F with CKD and hypokalemia presented with edema and hypokalemic NAGMA (bicarb 13 mmol/L, K 2.9 mmol/L). One year prior, she had CKD, proteinuria, and hypokalemia; evaluation, including serum protein electrophoresis, was negative. Kidney biopsy was read as focal AIN, attributed to NSAID use, and treated with prednisone.
On current presentation, creatinine was 1.4 mg/dL. UA showed pH 6.0 with 2+ protein and glucose, and no cells. UPCR was 7 g/g with UACR 280 mg/g. Serum phosphorus was low (1.8 mg/dL) with normal albumin and glucose, suggesting proximal tubular dysfunction.
Given these findings, a paraproteinemic process was suspected. Serum electrophoresis showed no M protein, but immunofixation revealed an atypical kappa band. Serum free kappa light chains were markedly elevated (10,338 mg/L) with kappa/lambda ratio >1000. Urine electrophoresis was also positive.
Biopsy re-review again showed negative immunofluorescence despite pronase digestion. However, electron microscopy (EM) demonstrated crystalline inclusions in proximal tubular cells and macrophages, consistent with crystalline LCPT with crystal-storing histiocytosis. Hematologic evaluation confirmed multiple myeloma, and clone-directed therapy was initiated.
Discussion
LCPT is a rare paraproteinemic kidney disease that presents with tubular dysfunction and progressive CKD. Diagnosis can be challenging, as immunofluorescence may be falsely negative due to the crystalline structure of deposits. Although antigen retrieval techniques may help, EM is often required to identify the characteristic crystalline inclusions.
The associated inflammatory response may mimic AIN, leading to misdiagnosis and inappropriate treatment. This case highlights the need for careful clinicopathologic correlation, including serum and urine monoclonal studies and expert pathologic review, to avoid diagnostic delay. Timely diagnosis is critical to prevent ongoing kidney injury and avoid inappropriate immunosuppression.