Diurnal variation in febrile convulsions.

This study sought to determine diurnal variations in febrile convulsions, and to investigate whether such variations influenced the severity of febrile convulsions. The study involved 326 children, between ages 6 months and 6 years, with simple febrile convulsions. Data were collected systematically by interviewing witnesses within the week after febrile convulsions occurred. The frequency of febrile convulsions was approximately 5 times greater in the evening than in early morning. An adaptation curve revealed that the maximum occurrence of febrile convulsions was at 4:00 pm (4:00-4:59 pm), and the minimum, at 4:00 am (4:00-4:59 am), similar to the pattern of human body temperature. Temperature and seizure duration did not differ significantly between high-frequency and low-frequency zones (2:00-7:00 pm and 2:00-7:00 am, respectively) (high-frequency zone vs low-frequency zone, 39.20 degrees C (S.D., 0.68 degrees C) vs 39.22 degrees C (S.D., 0.64 degrees C) and 3.82 minutes (S.D., 5.27 minutes) vs 3.14 minutes (S.D., 3.19 minutes)). These results suggest that the circadian rhythm does not change seizure propensity, but its hourly occurrence is attributable to an elevation in the temperature set point in the 24-hour period. The prevention of recurrent febrile convulsions by rectal administration of anticonvulsants in high-frequency zones would be clinically helpful.