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Seizures cycles occurred in more than 80% of people with epilepsy, a retrospective analysis found.

These cycles most often were circadian, but also included weekly and longer periods, reported Mark Cook, MD, of the University of Melbourne in Australia, and co-authors in .

"There are patterns to when epileptic seizures occur, but these are hard to recognize unless you collect lots of data," Cook told MedPage Today. "The patterns are important across the course of a day, but there are also patterns over weeks and months."

The analysis showed that seizure patterns are patient-specific and more common than previously thought, Cook noted: "What we first demonstrated in a small number of patients with an implantable system can be replicated in a large number of patients using a phone-based app. Once you have this information you will be better able to treat people, as you will be able to judge when to treat them."

While there has been extensive documentation about circadian (24-hour) patterns of seizures, longer cycles have been less frequently studied, he added. "We thought that cycles existed in women related to hormones, but in fact they are just as common in men. We don't yet know what controls these cycles."

The study used two databases of human seizures: one from , an online app that collects patient-reported seizure data; the other from intracranial electroencephalographic (EEG) monitoring devices that had been implanted in patients with intractable focal epilepsy. SeizureTracker patients (n=1,118) each had a minimum of 100 self-reported seizures. NeuroVista patients (n=12) each had at least 30 clinical seizures. SeizureTracker data was recorded from 2007 to 2015; NeuroVista data from 2010 to 2012.

Data analysis showed:

• At least 80% of SeizureTracker patients and 92% of NeuroVista patients showed circadian modulation of their seizure rates
• One NeuroVista patient had a significant cycle at precisely 1 week; two others had approximately 1-week cycles, and two had 2-week cycles
• Between 7% and 21% of SeizureTracker patients had strong circaseptan (weekly) rhythms showing a clear 7-day period
• Between 14% and 22% of SeizureTracker patients had significant seizure cycles that were longer than 3 weeks
• Seizure cycles were equally prevalent in men and women, and peak seizure rates were evenly distributed across all days of the week.

"Ultraslow oscillations in brain excitability are scarcely understood," observed Andreas Schulze-Bonhage, MD, PhD, of the University of Freiburg in Germany, in an . "Some evidence shows that such slow cycles (slower than well-known circadian rhythms) are relevant to many aspects of physiology and can influence disease states."

Identifying "such long-lasting cycling alterations in seizure propensity over several weeks, which have also been reported in chronic psychiatric diseases," is notable, especially the finding that "cycle durations of several weeks are not limited to women, in whom they might reflect catamenial hormonal changes, but also occur in men," he said.

already have been used to improve seizure prediction, Schulze-Bonhage added; in the future, this may help identify appropriate times for patients to perform activities safely or show periods for targeted therapy so drug concentrations could coincide with times of peak seizure propensity.

Much of this analysis relied on self-reported data from SeizureTracker, which is a limitation of the study, Cook and colleagues noted. The study also was limited to investigating trends of up to 3 months, so annual trends such as seasonal variations and daylight savings time were not assessed. Patients in both SeizureTracker and NeuroVista may not be typical of people with epilepsy.