When acute kidney injury in the intensive care unit is not acute tubular necrosis: A case report of κ-light chain crystalline tubulopathy
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Introduction: This case highlights the importance of getting a thorough workup for acute kidney injury before assigning a diagnosis. Case presentation: A 68-year-old male was referred to our clinic after a recent outside hospitalization for septic knee arthritis and acute kidney injury requiring hemodialysis. He had chronic kidney disease presumed secondary to diabetes with baseline GFR 50 mL/min. He complained of fatigue and weight loss. Vital signs were within normal limits. Exam was notable for trace ankle edema, healed right knee scar, and right internal jugular hemodialysis catheter. Medications included amlodipine, aspirin, atorvastatin, furosemide, sevelamer, and cephalexin. Calculated creatinine clearance was 6 mL/min with wine output 2 L/day. Urinalysis showed 1+ protein, 2+ glucose, and fine granular casts. Clinical impression was ischemic acute tubular necrosis in recovery phase. However, when he did not improve and continued requiring dialysis, further workup showed elevated serum kappa free light chains and urine Bence-Jones protein. Renal biopsy showed kappa light chain crystalline tubulopathy, interstitial inflammation, and extensive fibrosis. Subsequent bone marrow biopsy showed 15% kappa-restricted plasma cells. Multiple myeloma was diagnosed, and chemotherapy initiated. With decrease in kappa light chain burden. kidney function improved, and patient was able to come off dialysis. Conclusion: This case describes a rare presentation of kappa light chain crystalline tubulopathy and illustrates the value of a comprehensive evaluation for acute kidney injury to enable prompt diagnosis and therapy.