Seasonal changes of internet searching suggest circannual rhythmicity of primary headache disorders

Objective To investigate whether web searching for headache disorders presents some circannual rhythm. Background Studies support the influence of seasonal rhythms in primary headache disorders such as cluster headache (CH) and episodic migraine. We investigated whether internet users' searching for headaches reflect these circannual rhythms. Methods This was an internet-based study using the Google Trends (Google) platform. The 10-year interest across four related topics (headache, migraine, tension-type headache [TTH], and CH) in 31 European countries was scanned. Results Significant differences between months were found for the topics "headache" and "migraine." Interest in the former was superior in February (median for all countries, 61 [25th-75th percentile, 45-80]), October (61 [44-75]), and November (61 [45-76]). The lowest search volumes for headache appeared in July (52 [37-66]) (p < 0.001). Migraine was searched most commonly in November (56 [40-73]) and rarely in June (46.5 [31-64]) (p < 0.001). Differences were observed for the topic of headache in Northern Europe (p = 0.001) and for headache and migraine in Central Europe (p p = 0.016 respectively) but not in the southern region. TTH and CH were apparently less searched and no evident trends regarding them were present (median, 22 [0-44] for TTH and 15 [0-33] for CH; direct popularity comparison: headache 56 [44-63], migraine 16 [12-24], TTH 2 [1-2], and CH 2 [1-2]; between-month differences, p = 0.168 and p = 0.081 respectively). Conclusions Public attention on headache-related topics on the internet is distributed according to a significant trend of increased searching around spring and autumn. It suggests that a large number of patients may experience some level of seasonal variation in their headaches. Assessment of whether those temporal changes are present in clinical practice is necessary.