A Rare Case of Severe AKI Due to Crystal-Storing Histiocytosis

Introduction: We present an exceptionally rare case of acute kidney injury (AKI) requiring hemodialysis (HD) due to crystal-storing histiocytosis (CSH). Case Description: A 73-year-old woman with CKD stage 3b (baseline serum creatinine [SCr] 1.4 mg/dL) and hypertension was admitted for anorexia, failure to thrive, cognitive deficits, and stage 3 AKI initially attributed to poor intake for weeks. Labs showed SCr 14.2 mg/dL, BUN 95 mg/dL, urine protein-creatinine ratio 41 g/g (up from 0.3), hemoglobin 9 g/dL, and serum albumin 1.8 g/dL. Kappa-lambda ratio was 4.29 but with low-level IgG lambda M-protein on SPEP. HD was initiated. Kidney biopsy (figure) revealed kappa light chain-restricted crystal-storing histiocytosis with chronic active tubulointerstitial nephritis (TIN) and mild fibrosis. Bone marrow biopsy demonstrated 5-9% monoclonal CD138-positive kappa-restricted plasma cells. Skeletal survey was negative. She remains on HD after 5 weeks due to ongoing oliguria and azotemia. Treatment with Dara-CyBorD is planned. Discussion: Crystal-storing histiocytosis (CSH) is a rare pathologic entity characterized by the accumulation of non-neoplastic histiocytes containing intracytoplasmic crystallized immunoglobulins, typically associated with underlying monoclonal gammopathies and lymphoproliferative neoplasms. Though rare, any organ may be affected, with kidney involvement representing a rare form of monoclonal gammopathy of renal significance (MGRS). Though MGRS typically manifests as glomerular lesions, CSH most commonly affects the tubulointerstitium. Along with TIN, Fanconi syndrome has been reported. Though previously reported, AKI severe enough to require RRT is uncommon in renal CSH.A. Interstitial infiltrate. B, immunohistochemistry for CD68. C, immunofluorescence for kappa. D, crystals on toluidine blue stain.