Kidney Week

Abstract: FR-PO0869

Recurrent and Sequential Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)-Hypercalcemia of Malignancy: A Rare and Deceptive Presentation of Diffuse Large B-Cell Lymphoma

Session Information

• Fluid, Electrolyte, and Acid-Base Disorders: Case Reports - 1
  October 23, 2026 | Location: Exhibit Hall A, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Fluid, Electrolytes, and Acid-Base Disorders

• 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical

Authors

• Lugo-Guzman, Efrain G., University of the Incarnate Word, Laredo, Texas, United States

Efrain G. Lugo-Guzman, MD

• Senthilrajan, Ashwin Kumar, University of the Incarnate Word, Laredo, Texas, United States

Ashwin Kumar Senthilrajan, MD

• Gunturu, Akshay, University of the Incarnate Word, Laredo, Texas, United States

Akshay Gunturu, MBBS

• Sainz-Jacobo, Daniela, University of the Incarnate Word, Laredo, Texas, United States

Daniela Sainz-Jacobo, MD

• Zavala, Julio Paolo, University of the Incarnate Word, Laredo, Texas, United States

Julio Paolo Zavala, MD, FASN

• Cardenas, Armando Tomas, University of the Incarnate Word, Laredo, Texas, United States

Armando Tomas Cardenas, MD

Introduction

Difusse large B-Cell Lymphoma (DBCL) typically presents with lymphadenopathy, extranodal involvement occurs in up to 40% of cases and can produce paraneoplastic metabolic derangements that obscure the underlying diagnosis. We present a case of DLBCL with liver lessions presenting as recurrent hyponatremia and hypercalcemia.

Case Description

A 65-year-old woman presented with confusion and generalized weakness. Initial evaluation revealed severe hyponatremia (Serum osmolality [SOsm]: 271; Serum sodium [SNa]: 114), attributed to SIADH (Urine osmolarity[UOsm]: 480; Urine sodium [UNa]: 89) and hydrochlorothiazide was discontinued. Sodium was appropriately corrected, and the patient was discharged.
Five days later, she returned with recurrent severe symptomatic hyponatremia (SOsm: 241; SNa: 110); workup was consistent with SIADH (UOsm: 630; UNa: 139), with escitalopram identified as the likely culprit.
Four months later, the patient presented again with confusion and weakness. Electrolyteworkup revealed again SIADH hyponatremia (SOsm: 267, SNa: 122, UOsm 403, UNa: 34), but this time with severe hypercalcemia (total calcium: 15.5, ionized calcium: 7.7, PTH: 6, 25-HO Vit. D: 91), and AKI (creatinine: 3.0; baseline: 0.9). Management included calcitonin and zolendronic acid once renal function improved. CT of the chest was unremarkable; however, CT of the abdomen revealed hepatic lesions. PTHr, serum tumor markers and a myeloma workup were all negative. Liver biopsy was performed, which final result was pending when patient left against medical advice. Three months later, she presented with anasarca, worsening renal function (creatinine: 3.5), leukopenia, and anemia. The liver biopsy was revised, yielding a final diagnosis of diffuse large B-cell lymphoma.

Discussion

The concurrent presentation of SIADH and hypercalcemia is exceptionally rare, as these paraneoplastic syndromes exert opposed effects on renal free water handling. The initial attribution of hyponatremia to medication side effects, while reasonable, delayed recognition of an underlying malignant process. This case highlights the diagnostic complexity of DLBCL in the absence of overt lymphadenopathy and the need for a high index of suspicion for occult malignancy in patients with recurrent electrolyte disturbances, particularly when multiple metabolic derangements coexist.