Diurnal pattern of seizures outside the hospital: is there a time of circadian vulnerability?

OBJECTIVE: To evaluate whether the distribution of seizures throughout the day is the same in ambulatory outpatient conditions as observed in inpatient conditions.

METHODS: We analyzed records from consecutive patients who had ambulatory EEG monitoring for 24 to 72 hours using Digitrace™ EEG recording system. The participants maintained a log of symptoms and signaled the time when symptoms occurred by pushing an event button. Additionally, automatic seizure and spike detection was performed on each record using Persyst detection software.

RESULTS: Of 831 reports analyzed, 44 unique patients had definite ictal events. There were a total of 129 electrographic seizures (34 subclinical) with timing as follows: frontal (31), temporal (71), and generalized, posterior, or central (27). Frontal lobe seizures occurred more frequently between 12 am and 12 pm as compared to temporal lobe seizures, which occurred more frequently between 12 pm and 12 am (p = 0.017). Analysis of frontal lobe seizures revealed a cluster of 10 seizures centered at 6:33 am (range 5:15-7:30 am) with p = 0.0064. Temporal lobe seizures had a cluster of 24 seizures centered at 8:49 pm (range 6:45-11:56 pm) with p = 0.0437.

CONCLUSION: In ambulatory outpatient conditions, electrographic seizures follow day/night patterns similar to those observed in hospital conditions. Frontal seizures occur preferentially in the early morning hours and temporal lobe seizures occur in the early evening hours.