What are the prevalence, strength, and patterns of seizure cycles in focal epilepsy?
In this cohort study of 222 patients who received an implantable continuous electroencephalographic recording device, the prevalence was 12% of weak circannual seizure cycles, 60% of moderate multidien seizure cycles, and 89% of moderate circadian seizure cycles. Prevalent cycles were further classified into 5 multidien (7, 15, 20, and 30 days and irregular) and 5 circadian (morning, mid-afternoon, evening, early night, and late night) seizure chronotypes.
The findings establish the high prevalence of circadian and multidien seizure cycles and reveal the existence of distinct seizure chronotypes in focal epilepsy.
Focal epilepsy is characterized by the cyclical recurrence of seizures, but, to our knowledge, the prevalence and patterns of seizure cycles are unknown.
To establish the prevalence, strength, and temporal patterns of seizure cycles over timescales of hours to years.
Design, Setting, and Participants
This retrospective cohort study analyzed data from continuous intracranial electroencephalography (cEEG) and seizure diaries collected between January 19, 2004, and May 18, 2018, with durations up to 10 years. A total of 222 adults with medically refractory focal epilepsy were selected from 256 total participants in a clinical trial of an implanted responsive neurostimulation device. Selection was based on availability of cEEG and/or self-reports of disabling seizures.
Antiseizure medications and responsive neurostimulation, based on clinical indications.
Main Outcomes and Measures
Measures involved (1) self-reported daily seizure counts, (2) cEEG-based hourly counts of electrographic seizures, and (3) detections of interictal epileptiform activity (IEA), which fluctuates in daily (circadian) and multiday (multidien) cycles. Outcomes involved descriptive characteristics of cycles of IEA and seizures: (1) prevalence, defined as the percentage of patients with a given type of seizure cycle; (2) strength, defined as the degree of consistency with which seizures occur at certain phases of an underlying cycle, measured as the phase-locking value (PLV); and (3) seizure chronotypes, defined as patterns in seizure timing evident at the group level.
Of the 222 participants, 112 (50%) were male, and the median age was 35 years (range, 18-66 years). The prevalence of circannual (approximately 1 year) seizure cycles was 12% (24 of 194), the prevalence of multidien (approximately weekly to approximately monthly) seizure cycles was 60% (112 of 186), and the prevalence of circadian (approximately 24 hours) seizure cycles was 89% (76 of 85). Strengths of circadian (mean [SD] PLV, 0.34 [0.18]) and multidien (mean [SD] PLV, 0.34 [0.17]) seizure cycles were comparable, whereas circannual seizure cycles were weaker (mean [SD] PLV, 0.17 [0.10]). Across individuals, circadian seizure cycles showed 5 peaks: morning, mid-afternoon, evening, early night, and late night. Multidien cycles of IEA showed peak periodicities centered around 7, 15, 20, and 30 days. Independent of multidien period length, self-reported and electrographic seizures consistently occurred during the days-long rising phase of multidien cycles of IEA.
Conclusions and Relevance
Findings in this large cohort establish the high prevalence of plural seizure cycles and help explain the natural variability in seizure timing. The results have the potential to inform the scheduling of diagnostic studies, the delivery of time-varying therapies, and the design of clinical trials in epilepsy.
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Leguia MG, Andrzejak RG, Rummel C, et al. Seizure Cycles in Focal Epilepsy. JAMA Neurol. Published online February 08, 2021. doi:10.1001/jamaneurol.2020.5370
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