Clinical Scenario:
A 9-month-old infant is admitted with a 4-day history of profuse watery diarrhea and vomiting. The parents report that the child had poor oral intake and was unable to tolerate adequate oral rehydration solution (ORS). On examination, the infant is irritable with a high-pitched cry, has dry mucous membranes and doughy skin, but the anterior fontanelle is only mildly sunken. Peripheral pulses are well palpable, capillary refill time is 2 seconds, and there are no signs of shock. Laboratory investigations reveal: serum sodium 166 mmol/L, potassium 4.1 mmol/L, blood glucose 94 mg/dL, and serum osmolality 340 mOsm/kg. Intravenous fluid therapy is initiated. Twenty-four hours later, the serum sodium has decreased to 150 mmol/L, and the infant develops generalized tonic-clonic seizures.
What is the most likely cause of the seizures?
A. Cerebral edema
B. Hyperosmolar encephalopathy
C. Hypocalcemia
D. Hypoglycemia
E. Septic encephalopathy
Correct answer & Explanation:
Correct Answer: A. Cerebral edema
Explanation
This infant has hypernatremic dehydration (serum sodium 166 mmol/L). During treatment, the serum sodium decreased by 16 mmol/L within 24 hours, exceeding the recommended correction rate of 10–12 mmol/L per 24 hours (approximately 0.5 mmol/L/hour).
In hypernatremia, brain cells adapt by accumulating intracellular osmoles to maintain cell volume. Rapid reduction in serum osmolality causes water to move into brain cells, resulting in cerebral edema, which manifests as seizures, altered consciousness, or signs of raised intracranial pressure.
Why the other options are incorrect
A. Cerebral edema
Correct. Rapid correction of hypernatremia is the classic cause of seizures during treatment.
B. Hyperosmolar encephalopathy
Occurs before treatment due to severe hypernatremia and usually improves with appropriate correction.
C. Hypocalcemia
Can cause seizures but is not suggested by the clinical scenario.
D. Hypoglycemia
The blood glucose level is normal, making this unlikely.
E. Septic encephalopathy
There are no clinical features suggestive of sepsis.
Learning Point
Children with hypernatremic dehydration should have serum sodium corrected slowly, aiming for a fall of no more than 0.5 mmol/L/hour (10–12 mmol/L/day). Rapid correction increases the risk of cerebral edema, seizures, permanent neurological injury, and death.
