ICHD-3 definitions for episodic and chronic migraine

The distinction between episodic and chronic migraine is made when a person crosses a threshold of 15 monthly headache days, 8 of which meet the criteria for migraine.^{[IHS, 2018]} The division between episodic and chronic is therefore based on the frequency of the migraine symptoms.^{[IHS, 2018]} People with chronic migraine typically have worse disease outcomes, a more severe disease, and greater use of healthcare resources.^{[Katsarava et al., 2012]}

References:
Headache Classification Committee of the International Headache Society (IHS). The International Classification of Headache Disorders, 3^rd edition. Cephalalgia 2018; 38 (1): 1–211.

Katsarava Z, Buse DC, Manack AN, Lipton RB. Defining the differences between episodic migraine and chronic migraine. Curr Pain Headache Rep 2012; 16 (1): 86–92.

Other references used on slide:
Bigal ME, Lipton RB. Migraine chronification. Curr Neurol Neurosci Rep 2011; 11: 139–148.

Buse DC, Manack AN, Fanning KM, et al. Chronic migraine prevalence, disability, and sociodemographic factors: results from the American Migraine Prevalence and Prevention study. Headache 2012; 52 (10): 1456–1470.