0875 Age-Related Increase of Circannual Correlation Between Day Length and Severe Seizures Article Swipe

Introduction Recent work at Earth’s extreme poles in the northern and southern hemispheres has shown a significant correlation between increasing day length (i.e. solar time and severe seizures across the year with higher frequency during months of increasing day length). Age-wise, however, epilepsy prevalence is bimodal, peaking once in younger life and again in later life. It remains unknown whether the correlation between day length and seizure occurrence is uniform across the lifespan. Methods Secondary analysis of circannual severe seizure frequency from the Canadian Arctic (Kivalliq, Nunavut) in 2009-2020 (n=117) and New Zealand (Auckland) in 2015-2016 (n=361) dichotomized by age. Rayleigh’s test was conducted to assess for a statistically significant departure from circular uniformity (e.g. representing equal likelihood occurrence throughout the year) for each age group (e.g. older vs. younger than x-years-old) at each site, over different dichotomized age thresholds (x=30, 35, 40, 45). Results At each site, there was a significant correlation between increasing day length and severe seizure occurrence for the “younger” age group at the 30, 35, 40, and 45-year-old age thresholds. The respective mean resultant lengths in Kivalliq were 0.33 (p=0.018), 0.31 (p=0.012), 0.25 (p=0.028), and 0.24 (p=0.022) averaging calendar directions from April 8-15. In Auckland, the mean resultant lengths were 0.18 (p=0.0005), 0.18 (p=0.0002), 0.19 (p< 0.0001), and 0.17 (p=0.0005) averaging calendar directions from July 15-24. In contrast, there were no significant correlations in the “older” age group at either site for any age threshold. Conclusion There were significant and reproducible correlations of severe seizures with increasing day length after the respective winter solstices of the northern and southern hemispheres in the younger patient cohorts of the Canadian Arctic and New Zealand. In contrast, these correlations were lost in each older patient cohort at each site. These findings demonstrate an inverse age-dependent increase in the circannual link between day length exposure and severe seizures, which may suggest that environmental influences on seizure expression are stronger in younger individuals but degrade with age; for example, possibly from selective degeneration of retino-geniculo-hypothalamic afferents reportedly more attuned to zeitgebers from twilight, moonlight, and the seasons. Support (if any) None.