Seizure patterns in focal epilepsy include high rates of circannual, multidien cycles
A retrospective cohort study of more than 200 patients with medically refractory focal epilepsy that examined seizure patterns identified a “high prevalence” of plural seizure cycles, including multidien and circadian cycles.
The researchers published the study findings in JAMA Neurology.
“Focal epilepsy is characterized by the cyclical recurrence of seizures, but, to our knowledge, the prevalence and patterns of seizure cycles are unknown,” Marc G. Leguia, PhD, of the University of Bern in Switzerland, and colleagues wrote. “In the last decade, the availability of continuous electroencephalography (cEEG) provided a unique opportunity to study seizure cycles at long timescales with objective data and suitable statistics.”
Leguia and colleagues examined data from continuous intracranial EEG and seizure diaries for 222 adults with medically refractory focal epilepsy to establish the prevalence, strength and temporal patterns of seizure cycles over timescales of hours to years. Data collection occurred from Jan. 19, 2004, through May 18, 2018, with durations of up to 10 years.
The researchers recorded self-reported daily seizure counts, continuous EEG-based hourly counts of electrographic seizures and signs of interictal epileptiform activity (IEA), which varied between daily (circadian) and multiday (multidien) cycles. Outcomes included descriptive characteristics of cycles of IEA and seizures, specifically the prevalence, or the number of patients with a given type of seizure cycle; the strength, or the level of consistency with which seizures happened during different phases of an underlying cycle, which was measured as the phase-locking value (PLV); and seizure chronotypes, or the patterns in seizure timing at the group level.
The study population included 112 men; the median age in the study was 35 years (range, 18-66 years).
The prevalence of statistically significant seizure cycles included circannual patterns (12%), multidien (60%) and circadian (approximately 1 year; 89%). Leguia and colleagues found that strengths of circadian (mean PLV, 0.34 [SD, 0.18]) and multidien (mean PLV, 0.34 [SD, 0.17]) cycles were similar, while they reported a weaker strength for circannual cycles (mean PLV, 0.17 [SD, 0.10]).
Across participants, circadian seizure cycles demonstrated five peaks, including morning, mid-afternoon, evening, early night and late night. Multidien cycles of IEA revealed peak periods focused on 7, 15, 20 and 30 days. Regardless of multidien period length, self-reported and electrographic seizures routinely happened during the days-long rising phase of multidien IEA cycles.
The findings “establish the high prevalence of plural seizure cycles and help explain the natural variability in seizure timing,” according to Leguia and colleagues.
“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,” the researchers wrote.