ABSTRACT
Adverse events, particularly severe adverse events, after coronavirus disease vaccination are the primary concern for many patients. We present the first report of symptomatic hyponatremia, a potentially life-threatening condition, after administration of the ChAdOx1 nCoV-19 coronavirus disease-19 vaccine. A 24-year-old man developed altered consciousness and high-grade fever a day after receiving this vaccine. Computed tomography of the brain showed diffuse brain swelling with bilateral descending transtentorial brain herniation. His serum sodium level, urine sodium level, and urine osmolarity were 114 mEq/L, 77 mEq/L, and 230 mOsm/kg, respectively. He was diagnosed with symptomatic hyponatremia due to syndrome of inappropriate antidiuretic hormone. His symptoms rapidly improved after treatment with 3% NaCl. Seven days after admission, his serum sodium level was normal, and no further intervention was required. We believe that the vaccine was the trigger for hyponatremia in this case based on temporal relationship of vaccination and hyponatremia, the rapid improvement of the patient, and the transient nature of the hyponatremia. We postulate that cytokine underlies the pathophysiology of hyponatremia in this case. Recognition of adverse events after coronavirus disease-19 vaccination is essential. Symptomatic hyponatremia should be included in the differential diagnosis in altered-consciousness patients after administration of ChAdOx1 nCoV-19 coronavirus disease-19 vaccine.