Carbamazepine-induced hyponatremia following meningioma surgery: A case report

BACKGROUND Hyponatremia is a common postoperative electrolyte disturbance in neurosurgical patients and may present with nonspecific neurocognitive symptoms that overlap with intracranial complications. Carbamazepine (CBZ), frequently used for seizure prophylaxis and pain syndromes, is a recognized cause of drug-induced hyponatremia with a syndrome of inappropriate antidiuretic hormone secretion (SIADH)-like profile. CASE SUMMARY A 62-year-old woman underwent elective left supraorbital craniotomy and microsurgical resection of a left anterior skull-base meningioma. Postoperatively, CBZ 400 mg was initiated twice daily for antiseizure prophylaxis. On postoperative day (POD) 2, she developed somnolence and cognitive slowing with serum sodium 131 mmol/L, which progressed to 123 mmol/L (POD 3) and 119 mmol/L (POD 7) despite isotonic saline and increased dietary sodium. Hypertonic saline (3% NaCl) was introduced with partial correction. Evaluation confirmed hypotonic hyponatremia (serum osmolality 254 mOsm/kg) with inappropriately concentrated urine (urine osmolality 560 mOsm/kg) and elevated urine sodium (68 mmol/L) in a clinically euvolemic patient; thyroid and adrenal functions were normal. Given the temporal association and SIADH-like pathophysiology, CBZ-induced hyponatremia was considered the most likely etiology. CBZ was discontinued and replaced with levetiracetam (titrated to 500 mg twice daily), followed by clinical improvement and steady sodium normalization (132 mmol/L at discharge; 136 mmol/L by POD 19), remaining normal at three-month follow-up. We searched PubMed and Google Scholar to for relevant literature review. CONCLUSION This case highlights CBZ as a potentially reversible cause of significant postoperative hyponatremia after meningioma surgery. Early sodium monitoring after CBZ initiation and prompt substitution with alternative antiseizure therapy should be considered when euvolemic hypotonic hyponatremia develops in the postoperative period.