Abstract: FR-PO0957
Chronic Asymptomatic Hyponatremia in a Five-Year-Old Boy: A Case of Reset Osmostat Initially Mismanaged as Syndrome of Inappropriate Antidiuretic Hormone Secretion/Salt Wasting
Session Information
- Pediatric Nephrology: Genetic Diseases, Development, Neonatal Nephrology, Glomerular Diseases, and More
October 23, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Pediatric Nephrology
- 1800 Pediatric Nephrology
Authors
- Master Sankar Raj, Vimal, University of Illinois Chicago College of Medicine at Peoria, Peoria, Illinois, United States
- Miller, Mark, University of Illinois Chicago College of Medicine at Peoria, Peoria, Illinois, United States
Introduction
Chronic hyponatremia in pediatric patients often prompts investigation into Syndrome of Inappropriate Antidiuretic Hormone (SIADH) or cerebral salt wasting. However, "Reset Osmostat"—a variant of SIADH where the body maintains a lower-than-normal sodium set point—is a rare but important differential that prevents unnecessary and burdensome medical interventions.
Case Description
A 5-year-old boy presented with a history of persistent hyponatremia (serum sodium 127–132 mmol/L) noted on a screening lab when he presented for an acute illness. Past History significant for issues with meningitis and subsequent seizure as an infant from which he had fully recovered. His initial labs showed inappropriately elevated urine osmolality at 572 and high spot urine sodium of 112 mmol/L for a serum sodim of 127 mmol/L. Serum copeptin levels were normal at 6.3. Normal thyroid and adrenal function documented and an MRI brain was normal. He was initially managed under the assumption of SIADH/salt wasting with aggressive sodium supplementation, fludrocortisone, and fluid restriction. Despite these interventions his serum sodium never increased beyond 130. After a period of non compliance he was readmitted after sodium levels dropped to 127 mmol/L. At this time a water loading test was done. With water loading the patient demonstrated the preserved ability to dilute his urine (urine osmolality decreased from 881 to 303 mOsm/kg) while serum sodium remained stable. This confirmed a diagnosis of Reset Osmostat. All sodium supplements and fluid restrictions were discontinued. Follow up labs have remained stable with last sodium recorded at 131
Discussion
This case highlights the importance of considering Reset Osmostat in asymptomatic pediatric patients with "refractory" hyponatremia in spite of changes in sodium or water intake. Reset osmostat, a subtype of SIADH is characterised by a decrease of the threshold of plasma osmolality for the excretion of ADH.The majority of reported pediatric reset osmostat cases have been associated with midline defects such as cleft lip, cleft palate, corpus callosum agenesis or cyst in the hypothalmus. In our patient, our work up did not reveal a specific cause though there was a h/o infantile meningitis which could have contributed to the reset. A water loading test under close monitoring was able to show free water excretion establishing the diagnosis.