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The transformation or clinical progression of headache from episodic to “chronic daily headache” is a well-evidenced and long-recognized phenomenon.1-3 Citing several demonstrations of brain abnormalities in migraineurs (eg, brain infarction and white matter lesions, iron deposits in periaqueductal gray correlating with headache duration, central sensitization), Lipton and Pan4 suggested that clinical progression may be accompanied by progressive changes in the brain and that in some cases it could be conceptualized as a chronic progressive disorder. While migraine progresses in some patients, it does not progress in all or even most patients, leading Bigal and Lipton5 to conclude that migraine is best understood as a chronic disorder with episodic attacks and that it is progressive in some patients.

The conceptualization of migraine, chronic daily headache, and perhaps eventually other forms of chronic headache, as sometimes progressive disorders highlights the importance of identifying potentially modifiable risk factors associated with onset and progression, screening and risk factor modification (primary prevention), and early intervention to limit progression (secondary prevention). Clear identification of such risk factors could provide a foundation for the development of preventive interventions.5

Some of the risk factors for headache chronification identified to date are nonmodifiable (eg, age, low socioeconomic status, head injury), other risk factors have a key behavioral component that can be recognized and modified.5 Thus, screening and behavioral risk-reduction (ie, behavioral self-management) strategies may serve to prevent chronification. Analgesic overuse is probably the most widely recognized and best empirically established risk factor associated with chronification. Depression has long been implicated as a potential risk factor. More recent evidence has identified additional modifiable risk factors such as stressful life events, sleep variables, and obesity.

The papers presented in this series (entitled The Chronification of Headache: Mechanisms, Risk Factors, and Behavioral Strategies Aimed at Primary and Secondary Prevention of Chronic Headache) provide a substantive overview of the current state of the science addressing the progression of migraine. Two foundational papers in this series provide an overview of the concept and potential mechanisms of migraine progression6 and address the evidence pertaining to the various risk factors for this phenomenon – both modifiable and nonmodifiable.7 Five potentially modifiable risk factors are elaborated in supporting papers,8-12 each of which provide brief overviews of the current clinical science and summarizes the state of the art for screening and behavioral management of those risks. The risk factors addressed include substance overuse,8 sleep disorders,9 stress,10 psychopathology,11 and obesity.12 The concluding paper in the series provides a look to the future, addressing optimal research designs and recommending priorities for much needed future study within this critical arena.13

We thank John Rothrock, MD, Editor of Headache for his advice, support and encouragement for this endeavor, and Jason Roberts, PhD, managing editor of Headache for his wisdom, wit, and sage advice. Finally, we thank the contributors of the fine manuscripts included in this series.

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