One of the most important concepts that have developed recently in the field of
migraine is actually a definition of chronic migraine, a chronification of episodic
migraine. In fact, the International Headache Society suggests that the most important
risk factor for developing chronic migraine is having episodic migraine. And when we
start to look at people what we see is that they begin with nice, neat, clean episodes
of migraine that, over time, become more frequent and eventually they are having
migraine on more days than they are not. And hence, when migraine is occurring more
than 15 days out of a month, we now can call this chronic migraine.