The Epidemiology of Migraine And The Influence of Hormones
Migraine is a common, chronic neurovascular disorder that presents with recurrent attacks that are often disabling. Risk factors for migraine include those that are associated with migraine per se (e.g. disease risk factors) and those that are associated with individual attacks or attack frequency (e.g. triggers). Hormonal changes throughout the life cycle and during the menstrual cycle appear both to influence pain proneness and to act as an attack trigger. For some women, attacks are more frequent – or are exclusively experienced – during specific times of the menstrual cycle (Silberstein and Merriam, 1999). Pure menstrual migraine (PMM) is defined as attacks of migraine without aura that occur “exclusively on day 1+2 (i.e. days – 2 to +3) of menstruation in at least two out of three menstrual cycles and at no other times of the cycle.”
Menstrual related migraine (MRM) is defined as migraine without aura that occurs “day 1+2 (i.e. days -2 to +3) of menstruation in at least two out of three menstrual cycle and additionally at other times of the cycle.” MRM and PMM have been recognized in the International Classification of Headache Disorders, second edition, at least partly as a result of recent epidemiologic research (Headache Classification Subcommittee of The International Headache Society, 2004).
General Migraine Epidemiology
Incidence and Prevalence
Epidemiological studies have greatly advanced our knowledge about migraine and have significantly impacted therapeutic recommendations for patients. Often, epidemiological studies focus on the incidence or prevalence of a disease in a specific population over a defined time period. Incidence is the rate of new case of a disease in the at-risk population within a defined time period, while prevalence refers to the number of cases of a disease, both new and previously identified, that are present in a particular population at a given time. Most epidemiological studies of migraine measure 1-year prevalence, which is the proportion of the population meeting diagnostic criteria for migraine and who have had at least one attack in the last year. Some studies measure lifetime prevalence, which is the proportion of the population meeting diagnostic criteria for migraine, without the requirement of current or recent attacks. We first review the incidence and prevalence of migraine and then review the personal and societal impact that migraine may entail.
In the general population, data suggest that the incidence of migraine occurs earlier in males than in females and that the incidence of migraine with aura occurs earlier than the incidence of migrant without aura. In males, the incidence of migraine with aura has been shown to peak at 5 years of age (at 6.6/1000 person-years), while migraine without aura peaks at 10 to 11 years (at 10/1000 person-years). In females, migraine with aura peaks at 12 to 13 years (at 14.1/1000 person-years), while migraine without aura peaks at 14 to 17 years (at 18.9/1000 person-years). Similarly Breslau et al. (1991) showed that for any type of migraine, the mean age of migraine onset was almost 4 years earlier in boys than in girls. As the incidence of migraine peaks later in girls than in boys, the female-to-male preponderance that is seen in adult migraineurs is not evident in childhood; migraine in childhood is equally prevalent in girls and boys until approximately adolescence.
A recent study suggests that this pattern of increasing pain proneness after adolescence, at least in girls, may not be specific to migraine. LeResche and colleagues (2005) studied the relationship between pubertal development and the prevalence of four chronic pain adolescents (headache, facial pain, back pain, and stomach pain) in 11 to 17 year old adolescents identified from a managed care organization. Pubertal development was assessed using the Pubertal Development Scale (Petersen et al., 1988). Results showed that for both boys and girls pubertal development predicted the development of pain conditions better than age. In girls, pubertal development was positively associated with all four measured pain conditions. For boys, pubertal development was positively associated with facial pain and back pain and was negatively associated with stomach pain.
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