Interesting Case of Hyponatremia Corrected with Intravenous Contrast

Introduction: Hyponatremia is a common electrolyte disturbance encountered in clinical practice, often resulting from an imbalance between water intake and excretion. One rare but underrecognized cause is low solute intake, also known as tea and toast syndrome, where limited dietary solute impairs free water clearance. We report a unique case of hyponatremia due to low solute intake that unexpectedly corrected following administration of iodinated IV contrast during computed tomography (CT). Case Description: Our patient is a 44-year-old male with a past medical history of nasopharyngeal lymphoma who was admitted for chemotherapy. He was started on Dexamethasone, Etoposide, Isosfamide and carboplatin. His hospital course was complicated by altered mental status and communicating hydrocephalus. The patient was noted to have a sodium of 119 mmol/L. Work up revealed serum osmolality of 249 mosm/kg, urine osmolality of 175 msosm/kg, and an overall clinical picture consistent with poor solute intake. He received multiple CT with contrast studies for his lymphoma assessment. For each CT, he received 100 ml of Omnipaque 300 IV which has an osmolality of 640 msom/kg. Post IV contrast administration, the patient was noted to have large urine output measuring up to 7-8 liters a day. Repeat urine studies showed an increase in urine osmolality to 511 mosm/kg. There was an associated improvement in the sodium levels as well, gradually reaching 135 mmol/L. Given euvolemia, the increase in urine osmolality, and the large urine volume following IV contrast administration, polyuria was attributed to the IV contrast osmotic load resulting in correction of serum sodium. Discussion: This case illustrates the critical role of solute intake in water excretion and the pathophysiology of hyponatremia. The inadvertent correction following iodinated contrast administration likely resulted from the osmotic load of the contrast agent, which transiently increased solute delivery to the kidneys, promoting aquaresis. Given the slow rate of correction of serum sodium and the euvolemic status of this patient, the large urine output was appropriate and did not result in any adverse consequences. This case highlights the importance of recognizing low solute intake as a reversible cause of hyponatremia and raises awareness of how diagnostic interventions may unintentionally alter sodium balance.