Contributions of epidemiology to our understanding of migraine.

BACKGROUND: During the past decade, the introduction of the second edition of the International Classification of Headache Disorders (ICHD-II) and the initiation of active campaigns to increase awareness of the high magnitude, burden, and impact of migraine have stimulated numerous studies of population-based data on the prevalence, correlates, and impact of migraine.
OBJECTIVE: This paper provides an update of the literature on the worldwide epidemiology of migraine from studies that included the ICHD-II criteria. The aims of this paper are: (1) to review evidence regarding the magnitude of migraine; (2) to summarize information on the correlates and impact of migraine; and (3) to discuss the contributions, challenges, and future directions in the epidemiology of migraine. Evidence on the magnitude of migraine is divided into the following types of data: (1) prevalence rates of ICHD-II-defined migraine and tension-type headache from international population-based studies of adults; (2) the magnitude of migraine in U.S. studies; (3) ICHD-II-based international prevalence rates of ICHD-II-defined migraine in children; and (4) incidence rates of migraine from prospective longitudinal studies.
METHODS: A comprehensive review of the literature on the prevalence of migraine subtypes and tension-type headache defined by ICHD-II criteria during the past decade was conducted and aggregate weighted rates across studies were derived.
RESULTS: Across the 19 studies of adults that employed the ICHD-II criteria, the aggregate weighted estimates of the 12-month prevalence of definite migraine are 11.5%, and probable migraine of 7%, yielding a total of 18.5%. The cross-study weighted aggregate rate of migraine with aura is 4.4%, chronic migraine is 0.5%, and of tension-type headache is 13%. There has been even greater growth in international prevalence data on migraine in children, with a total of 21 studies of children that have employed the ICDH-II criteria. The aggregate weighted rate of definite migraine in children is 10.1% and migraine with aura is 1.6%. The well-established demographic correlates of migraine including the equal sex ratio in childhood, with increasing prevalence of migraine in females across adolescence to mid-adulthood were confirmed in these studies. Despite increasing effort to increase awareness of migraine, approximately 50% of those with frequent and/or severe migraine do not receive professional treatment.
CONCLUSIONS: This review demonstrates that the descriptive epidemiology of migraine has reached its maturity. The prevalence rates and sociodemographic correlates have been stable across 50 years. These developments justify a shift in efforts to the application of the designs and methods of analytic epidemiology. Retrospective case-control studies followed by prospective cohort studies that test specific associations are likely to enhance our understanding of the predictors of incidence and progression of migraine, subtypes of migraine with differential patterns of onset and course, and specific environmental exposures that may have either causal or provocative influences on migraine etiology.