Migraine is a common and disabling disorder that may be divided into 2 broad groups based on the number of headache days.1 If attacks occur less than 15 days per month the term episodic migraine (or simply migraine) is applied;when headaches occur on 15 or more days per month the terms chronic or transformed migraine (CM andTM ) are used.1,2 Since the revised definition of CM is relatively recent,3 most clinical observation and longitudinal studies assessed the chronic form of migraine as a chronic daily headache that evolved from episodic migraine, a process often referred to as transformation.4-6 Accordingly, herein we refer to TM instead of CM. In a single population study, the rate of transformation from episodic migraine toTM was around 3% per year,4 while in specialty clinics, it is as high as 14% per year.7 Identifying risk factors for migraine transition from an episodic into a chronic status is, therefore, a crucial step towards developing preventive strategies. Read more...