Abstract: FR-PO0866
A Rare Case of Severe Hyponatremia After Radiation Therapy
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
- Radhakrishna, Roshni, The Nephrology Clinic, Fort Collins, Colorado, United States
- Burgardt, Sara Tavernier, The Nephrology Clinic, Fort Collins, Colorado, United States
Introduction
Syndrome of Inappropriate Antidiuresis (SIAD) is the most common cause of hyponatremia in patients with cancer. Radiation treatment leading to hypothalamic osmoreceptor dysfunction is not described as a common cause of hyponatremia. Here we present a case of hyponatremia noted following radiation treatment for sinonasal carcinoma.
Case Description
A 76 year old female with history of poorly differentiated high grade sinonasal carcinoma presented to the hospital with acute encephalopathy and weakness 4 months following radiation therapy and was noted to have severe hyponatremia with serum sodium 120. She was euvolemic on exam with a Serum osmolality 256, Urine sodium 112 and Urine osmolality 629 suggestive of SIAD. She had no history of stroke, trauma or use of medications implicated in SIAD. Work up for hyponatremia was otherwise negative including TSH and cortisol. Of note her sinonasal tumor involved right ethmoid sinus and extended inferiorly into the right nasal cavity and superiorly through the cribriform plate into the anterior cranial fossa. She underwent neoadjuvant chemotherapy with cisplatin/etoposide followed by Endoscopic endonasal resection of cancer. Subsequently she underwent adjuvant chemoradiation with cisplatin (3 doses weekly) and radiation to the primary tumor bed in the paranasal sinuses and right nasal cavity. She was treated with fluid restriction and loop diuretics with gradual improvement in her sodium level to 125 in 24 hours. She was subsequently discharged on Urea with continued improvement in sodium to 130 range.
Discussion
SIAD is caused by impaired water excretion due to excess arginine vasopressin (AVP) or antidiuretic hormone (ADH) and is diagnosed in patients who present with hyponatremia, low serum osmolality, high urine osmolality >100 mosm/kg and urine sodium >40meq/L. Various causes include CNS disorders, drugs, ectopic production by tumors, surgeries and lung disorders. Radiation therapy for head and neck cancers can lead to radiation induced injury to surrounding organs. Our patient presented with severe hyponatremia 4 months after radiation to her post operative bed. Therefore SIAD was thought to be secondary to hypothalamic osmoreceptor dysfunction caused by radiation therapy for sinonasal cancer, leading to excess ADH and disruption of hypothalamic pituitary renal axis. AVP receptor antagonists can be considered for chronic management in addition to usual therapeutic modalities.