Low sodium levels in serum are associated with subsequent febrile seizures.

Fever plays an important role in causing disturbances in fluid and electrolyte balance. Hyponatraemia has been thought to enhance the susceptibility to seizures associated with febrile illnesses in childhood. We have studied serum electrolyte levels in children with simple and complicated febrile convulsions. Sodium levels were lower in those children with complicated convulsions in comparison with those having simple convulsions (136.07 +/- 3.06 mmoll-1, mean +/- SD, n = 42, and 137.62 +/- 2.63 mmoll-1, n = 71, respectively; p < 0.01, Student's t-test). The sodium concentrations were lowest in children with repeated seizures (134.20 +/- 2.30 mmoll-1, n = 15) compared with children having simple (p < 0.01, ANOVA, Duncan's test) or other complicated types of febrile convulsions: focal seizures (137.08 +/- 3.82 mmoll-1, n = 12, p < 0.01), seizures lasting longer than 15 minutes (138.00 +/- 2.45 mmoll-1, n = 5, p < 0.05) and children over 5 years (136.70 +/- 2.06 mmoll-1, n = 10, p < 0.05). Serum potassium levels showed no statistically significant differences between the patient groups. Our results show that hyponatraemia may increase the risk for multiple convulsions during the same febrile illness.