Global perspectives on the burden of episodic and chronic migraine

Recent studies have profiled chronic migraine (CM) and episodic migraine (EM) in many regions of the world using samples derived from various sources. In a previous issue of Cephalalgia, Wang and colleagues contrast patients with CM and EM recruited from two headache clinics in Taiwan (1). Their results add to the growing evidence indicating that, in comparison with EM, CM is less common but far more burdensome to individuals, as evidenced by measures of headacherelated disability, medical and psychiatric comorbidities, and health-related quality of life (HRQoL), and to society, as indexed by measures of lost productive time as well as direct medical costs. In 2011, the World Health Organization and Lifting the Burden Campaign against Headache published the ‘‘Atlas of Headache Disorders and Resources in the World 2011.’’ The authors of ‘‘The Atlas’’ stated, ‘‘Our view of the global burden attributable to headache disorders is incomplete. . .’’ (2). They urged researchers around the world to gather and publish data on the prevalence, burden, and other variables related to primary headaches in order to increase the understanding of the global status of headache prevalence, burden, costs, and care. They estimated the prevalence of headache on 15 days per month (an approximation of chronic daily headache (CDH)) in Southeast Asia to be 1.7% based on a compilation of data from epidemiological studies. CM is a form of CDH; however, ‘‘The Atlas’’ did not report rates of CM. In their recent systematic review of CDH and CM in the Asia-Pacific region, Stark and colleagues (3) identified two population studies, both from Taiwan, that reported the prevalence of CM as 1.7% (reported as transformed migraine (TM)) (4) and 1.0% (reported as CDH with migrainous features) (5). They also identified 19 clinic-based studies that reported rates and features of patients with CM. They concluded that Asia may have a lower prevalence of CM and CDH than the international average, although the rates of CM reported in the studies from Taiwan are similar to the prevalence of CM reported by the American Migraine Prevalence and Prevention (AMPP) study (6). Stark et al. also noted that CM was associated with significant headache-related disability, functional impairment, and psychiatric comorbidity in reports of clinic studies from Taiwan, Korea, and China. These findings from the Asia-Pacific region are similar to those reported by large international (7,8), North American (6), and European studies (9), which have also demonstrated that CM is associated with greater disease burden on multiple indices compared with EM. Making comparisons among studies and variations regions of the world is difficult because of variation in sources of study subjects and data collection methods among other factors. Fortunately, the AMPP study, the International Burden of Migraine Study (IBMS), and the study by Wang and colleagues collected and reported similar data, which allows for comparisons across studies. The AMPP study screened 120,000 United States (US) households selected to be representative of the US population and had a 64.9% response rate. Of 28,261 respondents who reported experiencing ‘‘severe headache’’ in the preceding year, 24,000 were followed annually from 2005 to 2009 with mailed, written questionnaires. The AMPP survey instrument was based on validated items from the American Migraine Studies 1 and 2 (10,11) along with validated questionnaires such as the Migraine Disability Assessment Scale (MIDAS) (12). The IBMS utilized a targeted, Webbased methodology to recruit and survey participants with EM and CM in 10 countries. Invitations were sent via email to 72,059 panelists. Of 23,312 respondents