- Patients with a history of chronic migraine meeting the diagnostic criteria listed in ICHD-III beta (2013) section 1, migraine (1), with the exception of ''complicated migraine'' (i.e., hemiplegic migraine, migraine with brainstem aura, ophthalmoplegic migraine-recurrent painful ophthalmoplegic neuropathy, migrainous infarction) will be enrolled. They are required during baseline to have ≥15 headache days with each day consisting of ≥4 hours of continuous headache and with ≥50% of days being migraine or probable migraine days; and ≥4 distinct headache episodes, each lasting ≥4 hours.