What is a chronic migraine?

Chronic migraine is where a patient experiences 15 or more headache days a month. On eight of those days they meet the criteria for migraine. The criteria for migraine include a headache that lasts between four hours and three days. It's typically one-sided, pulsating in nature, moderate to severe in intensity, and aggravated by or causes avoidance of routine physical activities, such as going up and down stairs. Headaches are also associated with either nausea and/or vomiting, or both light and sound sensitivity.