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Day/night patterns of focal seizures
Milena K Pavlova1, Steven A Shea, Edward B Bromfield
1Department of Neurology, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA. mpavlova1@partners.org
Purpose:
In many patients with epilepsy seizures occur with a day/night pattern. Our aims were to compare day/night patterns in seizure frequency among patients with different epileptogenic regions.
Methods:
We analyzed video-EEG recordings in 15 patients with temporal lobe (TLE) and 11 with extratemporal lobe epilepsy (XTLE). Each seizure was classified according to subject group (TLE vs XTLE), sleep/wake state, and time of day of seizure occurrence (grouped into 6 x 4-hour "bins").
Results:
Of 90 seizures, 41 occurred in TLE and 49 in XTLE patients. There were day/night patterns of seizure occurrence in each group, with differences in the patterns between groups. In TLE, 50% of seizures occurred between the hours of 15:00 and 19:00 (17% would be expected by chance in each 4-hour "bin": F=3.59, P<0.006). In XTLE, there was a peak between 19:00 and 23:00 (47%: F=4.72, P<0.0018). The effect of time on seizures was least pronounced in the XTLE patients who had more than one epileptogenic region. The proportion of seizures occurring from sleep was significantly less in TLE (19%) than in XTLE patients (41%) [P<0.04, Fisher's exact test].
Conclusions:
There are clear day/night patterns of seizure occurrence in epilepsy, with differences in the patterns between TLE and XTLE. There is an additional interaction with sleep/wake state, with relatively few seizures occurring from sleep in TLE compared with XTLE. Thus, it appears that both sleep/wake state and day/night or circadian rhythms may affect seizure proclivity, with different effects depending on the location of the epileptogenic region.