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Temporal distributions of seizure occurrence from various epileptogenic regions

From the Departments of Neurology (T.S.D., S.S.S., R.B.D., E.J.N., H.P.Z.), Neurosurgery (S.S.S., R.B.D., E.J.N., D.D.S.), and Pediatrics (E.J.N.), Yale University, New Haven, CT.

Address correspondence and reprint requests to Dr. Hitten P. Zaveri, Department of Neurology, 333 Cedar Street, Yale University, New Haven, CT 06520 hitten.zaveri{at}yale.edu

Objective: The aim of this study was to determine whether seizure occurrence in partial epilepsy is under the influence of circadian rhythms and rhythmic exogenous factors, and how this influence varies according to cortical brain region. For these ends, we determined and analyzed detailed temporal distributions of seizures arising from the frontal, parietal, occipital, neocortical temporal, and mesial temporal lobes.

Methods: We retrospectively analyzed intracranial EEG recordings from 131 consecutive adult subjects whose partial epilepsy was sufficiently localized for surgical resection. In all, 669 seizures were analyzed: 132 frontal, 77 parietal, 83 occipital, 217 mesial temporal, and 160 neocortical temporal.

Results: Seizure distribution was dependent on brain region (p < 10^–9). Nonuniform seizure distributions were observed in the parietal (p < 10^–4), occipital (p < 10^–7), mesial temporal (p < 0.02), and neocortical temporal lobes (p < 0.04). Occipital and parietal seizures occurred in strong gaussian-like distributions, 180° out of phase relative to each other; occipital seizure occurrence peaked between 16:00 and 19:00, whereas parietal seizures peaked between 4:00 and 7:00. Frontal lobe seizures followed a unimodal distribution, peaking between 4:00 and 7:00. Seizures from the mesial temporal lobe were distributed bimodally, with the primary peak in the late afternoon between 16:00 and 19:00 and secondary peak in the morning between 7:00 and 10:00. Neocortical temporal seizures peaked slightly before the primary peak observed in the mesial temporal lobe; however, these distributions did not differ significantly.

Conclusions: Seizure occurrence in partial epilepsy is not random. Endogenous circadian rhythms and rhythmic exogenous factors likely play substantial roles in seizure occurrence. These roles vary considerably according to brain region. Frontal and parietal lobe seizures seem most likely to occur nocturnally, whereas occipital and temporal lobe seizures seem to have strong afternoon preferences.

Abbreviations: MTLE = mesial temporal lobe epilepsy.

Supplemental data at www.neurology.org

Supported by NIH/National Institute of Neurological Disorders and Stroke grant R01 NS044102.

Disclosure: The authors report no conflicts of interest.

Received April 9, 2007. Accepted in final form August 23, 2007.