Migraine and Tension-Type Headache
Abstract and Keywords
This chapter provides information on the epidemiology of headache, with major sections devoted to migraine and tension-type headache. The clinical features of each headache type are discussed, and details of International Headache Society (IHS) criteria are described. This is followed by a summary of studies related to the incidence and prevalence, and a description of how headache frequency varies by age, sex, race, and geographic region. The chapter provides a summary of risk factors for headache, in addition to describing triggering factors among headache sufferers. The final section is devoted to a discussion of the impact of headaches, including frequency, severity, and health-related quality of life.
Headache is a pain symptom that virtually everyone experiences at one time or another. In 1988, the International Headache Society (IHS) (Olesen 1988) categorized the many causes of headaches, and two broad groups of headache disorders were distinguished: primary headache disorders and secondary headache disorders. In primary headache disorders, the headache disorder is the fundamental problem; it is not symptomatic of another cause. The two most common types of primary headache disorders are episodic tension-type headache (ETTH) and migraine. Secondary headache disorders are a consequence of an underlying condition, such as a brain tumor, a systemic infection, or a head injury. The underlying causes of secondary headaches determine their epidemiology; therefore, most neuroepidemiologic research has focused on the epidemiology of primary headache.
Approximately 36% of men and 42% of women aged 18 to 65 suffer from ETTH (Schwartz et al. 1998), while 18% of women and 6% of men aged 12 to 80 suffer from migraine (Stewart et al. 1992; Lipton and Stewart 1993). Tension-type headache has a modest impact on the individual; because the disorder is so prevalent, however, the aggregate impact of ETTH on society is high. Tension-type headaches (TTH) may also be chronic (CTTH) instead of episodic. Migraine headache is less common than tension-type headaches, but attacks are considerably more painful and disabling, often resulting in lost work time. Because the societal impact of both tension-type headache and migraine is significant, this chapter will focus on the epidemiology of these two disorders.
Migraine is a chronic disorder with episodic manifestations; it is characterized by attacks of head pain and various combinations of neurological, gastrointestinal, and autonomic changes. Although the IHS defines (p. 320 ) seven subtypes of migraine, by far, the two most important are migraine without aura and migraine with aura (see Table 13–1). Migraine is both a diagnosis of inclusion and exclusion. It is a diagnosis of inclusion because specific diagnostic features are required. It is a diagnosis of exclusion since secondary headache disorders have to be eliminated on the basis of the history, physical examination, or laboratory studies.
The gold standard for diagnosing migraine is assigned by a headache expert applying IHS criteria. In studies using videotaped patient encounters, the reliability of headache diagnosis is good to excellent (mean kappa = 0.74) but far from perfect (Granella et al. 1994). In epidemiology studies, a diagnosis of migraine is often assigned on the basis of a telephone interview or self-administered questionnaire. Using a clinical assessment as the gold standard, telephone interviews have sensitivities of approximately 85% and specificities of approximately 93% for migraine (Stewart et al. 1996a).
The migraine attack is often divided into four phases: the premonitory phase, the
Table 13–1 International Headache Society Diagnostic Criteria for Migraine with and without Aura
a. Migraine without aura
b. Migraine with and
Idiopathic, recurring disorder manifesting with attacks of neurological symptoms unequivocally localizable to cerebral cortex or brain stem, usually gradually developed over 5–20 minutes and usually lasting less than 60 minutes. Headache, nausea, and/or photophobia usually follow neurological aura symptoms directly or after a free interval of less than an hour. The headache usually lasts 4–72 hours, but may be completely absent.
Idiopathic, recurring disorder manifesting with attacks of neurological symptoms unequivocally localizable to cerebral cortex or brain stem, usually gradually developed over 5–20 minutes and usually lasting less than 60 minutes. Headache, nausea, and/or photophobia usually follow neurological aura symptoms directly or after a free interval of less than an hour. The headache usually lasts 4–72 hours, but may be completely absent.
In migraine with aura, focal neurological symptoms precede or accompany the attack. The aura develops over a period of 5–20 minutes and typically lasts less than 1 hour. Auras are usually visual and may include a mix of positive features (spots of light, zig-zag lines) and negative features (regions of visual loss). Auras may also involve other features, including motor, language, or brain stem disturbances. The aura is usually, but not always, followed by a headache. Approximately 20%–25% of migraine sufferers have migraine with aura. Most individuals who have migraine with aura also have attacks of migraine without aura (Johannes et al. 1995).
The third phase of the migraine attack is the headache phase. The headache of migraine is typically one-sided, throbbing, moderate to severe in intensity, and aggravated by routine physical activity. The headache phase may be accompanied by photophobia (sensitivity to light), phonophobia (sensitivity to sound), nausea, and vomiting, in variable combinations.
During the final phase, the resolution phase, the pain and accompanying symptoms subside. Many migraine sufferers report mood changes (euphoria, lethargy, fatigue) and scalp tenderness, even after spontaneous pain has subsided.
Estimating the incidence of a chronic disorder with episodic manifestations is challenging. Since diagnostic criteria for migraine without aura require at least five lifetime attacks, should incidence be estimated using the time of the first or fifth attack? Further, the disease affects individuals of all ages and the incidence rate varies substantially by age. To accurately describe incidence requires a large cohort study of individuals across the life span. There have been few studies of migraine incidence and no studies that systematically ascertain new migraine cases across a broad range of ages. The ideal study design for estimating the incidence of migraine would be prospective in design, ascertaining prevalent migraine cases at baseline and newly incident migraine cases as the study proceeded. As yet, no study has achieved this ideal in an inception cohort across a broad age span, but one study of migraine incidence was conducted in an inception cohort of young adults.
Example 13–1 Breslau et al. (1996) conducted a prospective study in 1007 members of a health maintenance organization. The inception cohort ranged in age from 21 to 30 years. Most of the sample (972/1007) completed follow-up interviews 3.5 and 5.5 years after enrollment. The at-risk population was composed of 848 participants who did not meet the criteria for migraine at baseline. The 5.5-year cumulative incidence was 8.4% (71/848; 60 female cases; 11 male cases), for a rate of 17.0 per 1000 person-years (24.0/102 female, 6.0/102 male). Of interest is that the female/male ratio of incidence rates was 4:1 in this study of young adults.
Two other population-based studies estimated the incidence of migraine using the reported age of migraine onset and reconstructed cohort methods. Using this method, a prevalence sample of migraine sufferers is identified and age of onset is determined, often by self-report. Self-reported age of onset is used to estimate age-specific incidence as described below.
Example 13–2 In Washington County, Maryland, telephone interviews were conducted (p. 322 ) among 10,169 residents between the ages of 12 and 29 to identify 392 males and 1018 females with migraine (Stewart et al. 1991). In both males and females, the incidence rate of migraine with aura peaked 3 to 5 years earlier than migraine without aura (Fig. 13–1). In addition, the incidence of migraine in females peaked at a later age than in males. The phenomenon of telescoping, or the tendency to report the occurrence of events in the past at times closer to the present (Brown et al. 1985), complicates incidence estimates derivedusing reconstructed cohort methods. Studies that estimate the age-specific incidence of migraine based on recall would likely be biased toward older ages of headache onset (Brown et al. 1985; Cummings et al. 1990). In the Washington County study, age-specific incidence rates were adjusted for the time lag between the reported age of onset and the age at interview. This study is still limited by the narrow age range of the participants.
Another population-based study, conducted by Rasmussen (1995), reported that the age-adjusted annual incidence of migraine was 3.7 per 1000 person-years (females 5.8/102; males 1.6/102). Neither age-specific incidence nor incidence by migraine subtypes was reported.
A third approach to estimating migraine incidence used medical records to ascertain cases. In the linked medical records system in Olmstead County, Minnesota, a review of 6400 patient records yielded 629 individuals who fulfilled criteria for migraine (Stang et al. 1992). The age-adjusted incidence rates were 1.37 per 1000 person-years for males and 2.94 per 1000 person-years for females. Only individuals who consulted a health-care provider for headache were included in this study, which may explain why these incidence rates are lower than in the previously discussed studies.
Although incidence studies of migraine have been few, many studies have estimated the prevalence of migraine. Prevalence is defined as the proportion of a given population that has migraine over a defined period of time. Studies have focused on lifetime and 1-year period prevalence.
Prevalence estimates for migraine have varied widely, largely because of differences in case definitions and demographic features of study populations. Since migraine prevalence varies by age, gender, race, geography, and socioeconomic status, prevalence differences among studies may be influenced by these factors (Stewart et al. 1995; Scher et al. 1999). The variations in migraine prevalence (p. 323 ) across studies could be due to many factors, including differences in case definition and study population features (i.e., age and gender distribution, geographic location).
Example 13–3 We conducted two meta-analyses of published population-based studies to examine the variation in prevalence among studies (Stewart et al. 1995; Scher et al. 1999). Our 1995 meta-analysis included 24 studies published prior to 1994, only 5 of which used the IHS diagnostic criteria. Figure 13–2 presents the age-specific migraine prevalence estimates among males (Fig. 13–2a) and females (Fig. 13–2b) from these population-based studies of migraine prevalence (Stewart et al. 1995). Clearly the prevalence estimates vary considerably among studies, making it difficult to draw conclusions about the true prevalence of migraine in the population. We used linear regression to estimate the proportion of variance in the age- and gender-specific prevalence ratios according to factors such as age, gender,(p. 324 ) case definition criteria, method of selecting the sample, source of sample, response method, response rate, time period for estimating prevalence, and whether the case was clinically confirmed. Interestingly, we found that over 65% of the variation in migraine prevalence among studies can be explained by remarkably few factors. The single most important factor, case definition, accounted for the largest portion of variation in prevalence (36%) among studies. Other important factors included gender (15%) and age (age 3%; age2 14%). Migraine was more prevalent among females than males, peaking between 35 and 55 years of age in both genders. Methodologic factors, such as the source of the population, the response rate, and whether diagnoses were confirmed by a clinical examination, did not have significant explanatory power.
In a second meta-analysis conducted in 1998, we included 18 population-based studies, all based on the IHS criteria (Scher et al. 1999). In this meta-analysis, case definition was held relatively constant and separate meta-analyses were conducted for males and females. Thus, the two most important explanatory factors in the first meta-analysis (case definition and gender) were eliminated. In this second meta-analysis, among both females and males, prevalence peaked during the third and fourth decades of life. For females, age and geographic location of the study population accounted for 74% of the variation in migraine prevalence. For males, these two variables accounted for 58% of the variation in migraine prevalence. Assessment of geographic location revealed that migraine prevalence was highest in North America, South America, and Western Europe, intermediate in Africa, and lowest in Asia, as discussed below. Once again, variation in migraine prevalence was not explained by methodological factors such as sampling method, response method, response rate, and recall period. Socioeconomic status, cultural differences in symptom reporting, or other unmeasured factors may help account for the residual variation in migraine prevalence (Stewart et al. 1995; Scher et al. 1999).
Prevalence by Age and Gender.
Migraine prevalence varies by age and gender. At post-pubertal ages, migraine prevalence is consistently higher in females than males (Scher et al. 1999). The prevalence of migraine varies with age, peaking between the ages of 35 to 45 years. Overall, prevalence is highest from 25 to 55, the peak years for economic productivity. This age distribution may account for the enormous economic impact of migraine due to absenteeism and reduced productivity at work.
Prevalence by Race and Geographic Region.
Race and geographic region contribute to variation in migraine prevalence. A population-based study in the United States compared the prevalence of migraine among Caucasians, African Americans, and Asian Americans living in Baltimore County, Maryland. Both before and after adjusting for sociodemographic covariates, prevalence of migraine was lowest in Asian Americans (female 9.2%, male 4.8%), intermediate in African Americans (female 16.2%, male 7.2%), and highest among Caucasians (female 20.4%, male 8.6%). These results mirror the meta-analytic finding that prevalence is lowest in Asia and Africa, with considerably higher prevalence in Europe, Central/South America, and North America (Scher et al. 1999).
What accounts for the international variation in migraine prevalence? Sociocultural factors, such as diet, stress, or other environmental factors, may account for the variation. Alternatively, differences in genetic susceptibility may play a role. The relative contributions of genetic and environmental risk factors or their interactions to the observed patterns of migraine prevalence remain to be determined.
Prevalence by Education and Income.
Population-based studies conducted in North America indicate that migraine prevalence is inversely related to household income or education (Stewart et al. 1992, 1996a; Lipton and Stewart 1993; Kryst (p. 325 ) and Scherl 1994). That is, as income or education increases, migraine prevalence declines. This population finding contradicts prior beliefs regarding a direct relationship between income and migraine prevalence. This discrepancy may be explained by patterns of health-care utilization. Migraine may appear to be a disease of high income in the doctor’s office, because medical diagnosis of migraine is more common among high-income groups (Lipton et al. 1992). Results of the National Health Interview Survey (NHIS) (Stang and Osterhaus 1993) support the hypothesis that patterns of consultation may shape physicians’ perceptions. In the NHIS study, migraine prevalence was lower in the low-income group than in the middle-income group, and was highest in the high-income group. Since this study relies on self-reported medical diagnosis, the higher prevalence among the high-income group may be due to an increased likelihood of diagnosis of migraine as income rises. Studies outside the United States have not generally reported the inverse relationship between migraine prevalence and income (Rasmussen 1992; Abu-Arefeh and Russell 1994; Gobel et al. 1994; O’Brien et al. 1994). Reasons for this international variation are unclear.
Risk Factors for Developing Migraine
Risk factors for migraine should be distinguished from risk factors that trigger the episodic attacks of headache within people who suffer from migraine (Olesen et al. 1993; Rasmussen 1995). Positive family history, female gender, epilepsy, depression, and low socioeconomic status are associated with developing chronic migraine (Rasmussen 1995; Breslau and Rasmussen 2001).
Over the last decade, some progress has been made in defining risk factors for the disease. Numerous studies have examined the socioeconomic profiles, comorbidities, and genetics of migraine (Olesen 1993; Lipton and Stewart 1997; Breslau and Rasmussen 2001). Migraine is emerging as a clinically and biologically heterogenous disorder, however, further advances are still needed to identify and quantify the contributions of factors that cause the development of migraine.
Genetic risk factors may be involved in migraine. Studies have found that various headache types and migraine tend to aggregate within families (Russell and Olesen 1995, 1996; Stewart et al. 1997; Russell et al. 1999). This has raised the question of whether this is due to environmental or genetic origins (or both). While an active search is underway to identify genes that cause migraine, no definitive results have been published.
Triggering Factors among Migraine Sufferers
For an individual who suffers from migraine headaches, certain factors may trigger an attack (see Table 13–2), including endogenous (e.g., menses) and exogenous factors (e.g., diet, fatigue, stress, and seasonal changes) (Lipton 2000; Breslau and Rasmussen 2001). Migraine sufferers are eager to understand what initiates their attack. Identifying the precipitating factors can lead to preventive strategies such as trigger avoidance, stress management, and short-term prophylaxis of menstrual migraine, and can enhance feelings of self-control (Olesen 1993; Lipton and Stewart 1997).
The most common method used to investigate trigger factors is patient surveys (Van den Bergh et al. 1987; Rasmussen 1993) in which migraine sufferers are asked to list their headache triggers and whether specific listed factors trigger their migraine attacks. In some cases, a clinician may conduct an N-of-1 study that helps suggest whether a factor triggers headaches or not. However, these studies are notorious for not providing clear evidence.
Example 13–4 In a study to determine the effect of Chinook weather conditions on the probability of developing a migraine (p. 326 )headache, 88% of the participants reported that the Chinook weather influenced their migraine (Cooke et al. 2000). However, using rigorous diary methods, Chinook weather precipitated migraine in only 29% of the participants. Thus, migraine sufferers may differentially recall only the attacks that support their belief that a particular putative factor triggered their migraine headache.
Table 13–2 Risk Factors and Triggering Factors for Migraine
Risk factor or trigger
Xanthine-containing foods (wine, chocolate, tea, coffee, colas)
Tyramine-containing foods (cheese, bean pods)
Preservatives (sulfites, nitrates)
Pickled or fermented foods
Flavor enhancers (aspartame, MSG)
Exposure to smoke
Food consumption patterns (e.g., meal skipping)
Overuse of pain or analgesic agents
Physiological and psychological factors
Randomized clinical trials are often conducted to examine exogenous triggers of migraine (Lipton 2000). Subjects are exposed to a placebo or to a trigger factor, such as aspartame, chocolate, or nitroglycerine (Olesen 1993; Van Den Eeden et al. 1994; Rasmusssen 1995). When only one trigger is tested, inferences about between-group differences in migraine occurrence with and without exposure to the factor may be possible. However, multiple exposures to the trigger factor for each patient is a better design to support inferences about individual patients. In any case, well-controlled trials that are blinded and adequately controlled are needed to assess these factors. Study designs such as crossover trials, if appropriate, or diary studies that have the participants blinded to the hypothesis can greatly enhance the believability of these putative associations.
Individual Impact-Frequency and Severity of Attacks
Migraine is a disabling disorder with an impact on both the individual and society. The individual impact of migraine is measured by quantifying the symptom profile and the frequency and severity of attacks, as well as through quality of life studies.
The individual impact of migraine has been evaluated in numerous studies (Stewart et al. 1992, 1994, 1996b; Lipton and (p. 327 ) Stewart 1993). In a population study of 1748 migraine sufferers identified by telephone interview, approximately 40% of subjects (female 39%; male 46%) reported severe pain, while an additional 40% reported very severe pain (female 43%; male 32%). The remainder of subjects reported pain that ranged from mild to moderate.
Most migraine sufferers reported a range of symptoms other than pain including photophobia (overall 82%; female 84%; male 77%) and phonophobia (overall 78%; female 79%; male 73%). More than half (59%) of migraine sufferers reported nausea that accompanies their migraine headache more than half of the time (female 62%; male 47%), while only a small proportion reported vomiting.
Most subjects reported one to two migraine attacks per month. The duration of an untreated attack varies considerably by gender. Among females, approximately 71% of attacks last longer than 24 hours. In contrast, 48% of males reported attacks that last longer than 24 hours. These results are comparable to the results of previous studies (Stewart et al. 1992, 1994; Lipton and Stewart 1993).
There have been at least three population-based studies of health related quality of life (HRQoL) in migraine cases versus controls (Terwindt et al. 1998; Lipton et al. 1999a; Steiner et al. 1999). In all of these studies, migraine sufferers had substantially lower HRQoL relative to population controls. In addition, HRQoL was inversely related to attack frequency and disability (Terwindt et al. 1998; Lipton et al. 1999a). One clinic-based study (Osterhaus et al. 1994) found that migraine sufferers have HRQoL scores similar to patients with osteoarthritis, hypertension, or diabetes. However, HRQoL measured in clinic-based samples may differ from that of migraine sufferers in the community. In addition, many studies conducted in clinic-based samples lack a contemporaneous control group derived from the same source population or sample (e.g., neurology clinic).
Economic Impact of Migraine Headache
The direct costs of migraine care may include outpatient visits, hospitalization, the use of emergency department services, the cost of prescriptions and diagnostic tests, as well as other treatments. For migraine, most of the direct costs are due to outpatient visits and the cost of prescription medications, rather than hospitalization (Stang and Osterhaus 1993; Clouse and Osterhaus 1994), or are due to the use of emergency department services (Celentano et al. 1992; Edmeads et al. 1993; Clouse and Osterhaus 1994).
Few studies have assessed medical care for migraine in economic terms. In a population sample, Hu et al. (1999) estimated the annual costs of migraine treatment. They found that the annual treatment costs for migraine were over $1 billion, about $100 per migraine sufferer per year. These are likely to be underestimates because the figures were derived from 1994 data, and consultation and medication use have increased substantially over recent years (Lipton et al. 1999b). Clouse and Osterhaus (1994) reported similar, though slightly higher, average claim costs per member per month ($145). Since migraine sufferers are likely to have comorbid conditions, the increased costs may reflect the costs due to the treatment of migraine as well as other medical conditions.
Lost productivity time is the major determinant of the indirect economic impact of migraine. When estimating indirect costs, it is important to account not only for lost workdays due to migraine (absenteeism) but also reduced productivity while at work. Some studies have asked patients to report absenteeism or reduced production over 1 year; however, the accuracy of recall over this period is uncertain (Rasmussen et al. 1992; Stewart et al. 1996b; Schwartz et al. 1997). For some purposes, it is desirable to combine lost workdays (absenteeism) and reduced effectiveness days into an overall measure, often termed lost workday equivalent (LWDE). The (p. 328 ) LWDE equals the total days of missed work plus the number of days at work with headache multiplied by the estimated decrease in percent effectiveness for working with headache (Stewart et al. 1996b).
Example 13–5 To circumvent limitations of prior studies, Von Korff et al. (1998) conducted a population-based diary study. Individuals recorded missed time from work and reduced productivity on a daily basis for 3 months. During this 3-month period, migraine sufferers missed an average of 1.1 days per month due to headache. Subjects who worked during a migraine attack reported work effectiveness that was reduced by an average of 41 %. The missed workday and LWDE estimates reported by Von Korff et al. (1998) are higher than those reported in other population-based studies (Osterhaus et al. 1992, Stang and Osterhaus 1993; van Roijen et al. 1995, Stewart et al. 1996b). The use of a daily diary may have improved the accuracy of reporting, which is inherently limited by asking people to recall events over the past 3 to 12 months. A relatively small percentage of migraine sufferers account for the majority of lost work time. In this study, the most disabled 20% of the participants accounted for 77% of the missed workdays; 40% of subjects accounted for 75% of the total LWDEs (Von Korff et al. 1998).
Recently, Hu et al. (1999) used the human capital method to estimate the indirect costs of migraine. These studies assume that the economic value of a missed day of work is equivalent to the lost wages for that day. According to the results of this population-based study, Hu et al. estimated that migraine costs American employers $13 billion per year because of absenteeism and reduced effectiveness at work. Approximately 62% of the cost was due to absenteeism. Importantly, the greatest indirect costs were found among middle-age (30–49) individuals. Although this study provided important information, the human capital method values the indirect costs of the disease according to the sufferers’ salary. A lost workday is valued by the individuals’ wages for that day, therefore the impact of the disease in a laborer or homemaker would be valued lower than that of a business executive with a high salary. A limitation of all studies reported to date is that reduced productivity while at work when suffering from a migraine is based on self-report. No studies to date have actually quantified reductions in productivity.
Tension-type headache (TTH) is diagnosed on the basis of a characteristic symptom profile and the exclusion of secondary headache (Table 13–3). In TTH, there is no prodrome or aura. The headache is usually bilateral, with pressing, tightening, or squeezing pain of mild to moderate intensity. Tension-type headaches are of two major forms, episodic tension-type headache (ETTH) and chronic tension-type headache (CTTH) (see Table 13–3). The major difference between these disorders is the frequency of headache attacks. If headaches occur less than 15 days per month, they are classified as ETTH, while those that occur 15 or more days per month are classified as CTTH. For ETTH, nausea excludes the diagnosis but one of either photophobia or phonophobia is permitted. For CTTH, any one of nausea, photophobia, or phonophobia may occur; if more than one of these features is present, the diagnosis is excluded.
Most subjects with ETTH (90%) report mild to moderate headache pain; attacks typically occur 3 times per month (Rasmussen et al. 1991; Gobel et al. 1994; Lavados and Tenhamm 1998; Schwartz et al. 1998). Chronic tension-type headache, by contrast, is typically associated with higher pain intensity and more frequent attacks. By definition, CTTH headache frequency ranges from 15 to 30 headaches per (p. 329 )
Table 13–3 International Headache Society Diagnostic Criteria for Episodic Tension-Type Headache and Chronic Tension-Type Headache
a. Episodic tension-type headache
b. Chronic tension-type headache
Recurrent episodes of headache lasting minutes to days. The pain is typically pressing/tightening in quality, of mild or moderate intensity, and bilateral in location, and it does not worsen with routine physical activity. Nausea is absent, but photophobia or phonophobia may be present.
Headache is present for at least 15 days a month for at least 6 months. The headache is usually pressing/tightening in quality, mild or moderate in severity, and bilateral, and it does not worsen with routine physical activity. Nausea, photophobia, or phonophobia may occur.
The clinical profile of TTH varies by gender. Bilateral pain occurs in most TTH sufferers, but occurs with even greater frequency among women than among men (Lavados and Tenhamm 1998). Throbbing pain occurs approximately equally in 66% of men and 57% of women; this feature, often viewed as a hallmark of migraine, poorly discriminates the two disorders. Pressing pain is also frequently reported. Many subjects with TTH report that pain is exacerbated with movement (men, 70%; women, 76%), which is surprising since pain that is exacerbated by movement is normally associated with migraine rather than TTH. Photophobia or phonophobia is common, especially in women. If both features are present simultaneously, the diagnosis of TTH is excluded; however, each feature occurs in isolation with surprising frequency.
(p. 330 ) Prevalence
Published studies of the epidemiology of TTH have produced estimates for the 1-year period prevalence, which range between 14% (Lavados and Tenhamm 1998) and 93% (Rasmussen et al. 1991) for ETTH and 0% (Tekle-Haimanot et al. 1995; Lavados and Tenhamm 1998) to 8% (Tekle-Haimanot et al. 1995) for CTTH. Variation in prevalence estimates may be due in part to differences in study methodology. Lifetime prevalences are higher than 1-year period prevalences. Demographic factors, such as age of the population, influence prevalence estimates, and case definition, also plays a role. Studies have used various levels of diagnostic specificity; some studies group all TTH (IHS 2.0) subjects together, while other studies distinguish between subjects with ETTH, (IHS 2.1), those with CTTH (IHS 2.2), and those with headache of the tension type fulfilling all criteria except one (IHS 2.3). Data collection methods may also influence prevalence estimates. Methods of data collection (e.g., self-administered questionnaires, telephone interviews, and clinical examinations) as well as the quality of data collection contribute to variation in diagnostic accuracy. Finally, the source of the study population, community based or clinic based, is likely to cause varying prevalence estimates.
There has been one large-scale population survey in the United States describing the epidemiology of IHS-defined ETTH and CTTH (Schwartz et al. 1998). Data from a telephone interview survey of 13,345 residents of the Baltimore County, Maryland area (Stewart et al. 1996a) were used to estimate the 1-year period prevalence of ETTH and CTTH by gender, age, education, and race. The 1-year period prevalence of ETTH in the past year was 38%.
In Santiago, Chile, Lavados and Tenhamm (1998) conducted in-person interviews in a representative sample of 1385 adults (>14 years old). Subjects reported details about the type of headache they suffered most often. The 1-year prevalence of ETTH was 24%. The lower prevalence in this study compared to the U.S. study (Schwartz et al. 1998) may be explained by differences in case definition. In Santiago, only a subject’s most common type of headache was eligible to be classified. Classification based on a single headache type in the U.S. study yielded a prevalence estimate of 25% vs. 38% after the second headache type was classified.
In a Danish study, prevalence estimates for ETTH were higher than in most other studies (Rasmussen et al. 1991). Potential participants were identified from the Danish National Central Person Registry and invited to a general health examination, with an emphasis on headache. In this study of 740 subjects, the 1-year period prevalence of ETTH was 74%. Since potential subjects were invited to a health exam with an emphasis on headache, individuals who had headaches may have been more likely to participate.
The prevalence of CTTH is markedly lower than that of ETTH. Across studies, 1-year period prevalence estimates range from 1.7%–2.2% (Rasmussen et al. 1991; Takle-Haimanot et al. 1995; Lavados and Tenhamm 1998; Schwartz et al. 1998; Castillo et al. 1999). Overall, 4% to 5% of the population reports headaches 15 or more days per month (Castillo et al. 1999).
Prevalence by Age and Gender.
The prevalence of both ETTH and CTTH varies with gender and age. Tension-type headache is slightly more common among females than among males. For example, in the United States, 42% of females and 36% of males have ETTH, yielding an overall gender prevalence ratio of 1.16 (Schwartz et al. 1998). The female preponderance occurs at all ages and educational levels and in all races. Several other studies also reported a higher prevalence of TTH among women (Rasmussen et al. 1991; Pryse-Phillips et al. 1992; Wong et al. 1995; Barea et al. 1996; Wang et al. 1997; Lavados and Tenhamm 1998), with female-to-male gender ratios (p. 331 ) ranging from 1.25 (Rasmussen et al. 1991) to 1.9 (Lavados and Tenhamm 1998).
The female preponderance for CTTH is substantially greater than that of ETTH. For example, in the United States, the prevalence of CTTH was reported at 2.8% in women and 1.4% in men, for an overall gender prevalence ratio of 2.0 (Schwartz et al. 1998). Other studies have also reported a female preponderance in CTTH (Tekle-Haimanot et al. 1995; Lavados and Tenhamm 1998; Castillo et al. 1999). The female preponderance in CTTH falls between that of ETTH and migraine.
The prevalence of TTH may vary by age, though results are inconsistent across studies. Several studies showed that TTH prevalence peaks in the 30s and 40s, with a decline thereafter (Pryse-Phillips et al. 1992; Wong et al. 1995; Lavados and Tenhamm 1998; Schwartz et al. 1998). One study suggested that prevalence decreases with age (Rasmussen et al. 1991), and one found no difference in prevalence by age (Gobel et al. 1994). The lack of association with age in the latter study may be due to the use of wider age groupings than that in the other studies (20-year intervals vs. 10-year intervals).
Several authors reported that the prevalence of CTTH increases with age (Tekle-Haimanot 1995; Lavados and Tenhamm 1998; Schwartz et al. 1998). Perhaps individuals develop ETTH, which gradually increases over time until criteria for CTTH are met (Langemark et al. 1988; Rasmussen 1995).
Prevalence by Race and Geographic Region.
Geographic and racial differences may account for part of the variation in the prevalence of TTH among studies. According to the results of reported studies, prevalence appears to be highest in the Western Hemisphere (Pryse-Phillips et al. 1992; Lavados and Tenhamm 1998; Schwartz et al. 1998) and Denmark (Rasmussen et al. 1991), and lowest in the Asian countries (Wong et al. 1995).
A U.S. study examined prevalence of TTH by race (Schwartz et al. 1998). The prevalence of ETTH was significantly higher in whites than in African Americans in both men (40% vs. 23%) and women (47 vs. 31%). The prevalence of CTTH by race paralleled the observations for ETTH: prevalence was higher in whites than in African Americans in both men (1.6% vs. 1.0%) and women (3.0% vs. 2.2%).
Prevalence by Education.
The relationship between socioeconomic status and the prevalence of ETTH varies among studies. Schwartz et al. (1998) used educational level as a measure of socioeconomic status. Prevalence was directly related to education, peaking in those with a graduate-level education (men 48.5%; women 48.9%). Similarly, Lavados and Tenhamm (1998) found a direct relationship between ETTH prevalence and socioeconomic status. Other studies have not found this direct association (Pryse-Phillips et al. 1992; Gobel et al. 1994). A German study using only two educational categories (i.e., basic and secondary) did not find such a relationship (Gobel et al. 1994), but this approach may have lacked the power to detect an effect. The influence of socioeconomic status may also vary by country.
The socioeconomic pattern for CTTH is different from that of ETTH. Two studies reported that the prevalence of CTTH declined with increasing educational level, especially among women (Lavados and Tenhamm 1998; Schwartz et al. 1998). This pattern is similar to findings in migraine. Schwartz et al. (1998) suggested that the epidemiology of CTTH, with its higher risk in women and strong relationship to socioeconomic status, has an epidemiologic profile intermediate between that of ETTH and migraine and may reflect the progression of both headache types to a chronic form.
Economic Impact of Tension-type Headache
The first population-based study to examine work loss data in ETTH was reported by Rasmussen et al. (1992) in Denmark. (p. 332 ) Among employed participants, 12% were absent from work at least once during the previous year because of ETTH. Of those who missed work, the majority (68%) were absent from 1 to 7 days during the previous year. Twenty-five percent (25%) were absent between 8 and 14 days during the year, and only 16% were absent more than 14 days during the previous year.
Schwartz et al. also measured the impact of headache in the workplace in a study conducted in Baltimore County, Maryland (Schwartz et al. 1997, 1998). Reduced ability to function and inability to function (actual missed work) were measured separately. Of the lost work time associated with headache, 19% of the missed workdays and 22% of the reduced-effectiveness days were specifically due to ETTH (Schwartz et al. 1997). Among subjects with ETTH, 8% reported missed workdays (absenteeism), while 44% reported reduced-effectiveness days at work due to headache. Among those with missed workdays, an average of 8.9 missed workdays were reported, while subjects with reduced-effectiveness days reported approximately 5.0 reduced-effectiveness days per person. Lavados and Tenhamm (1998) found higher levels of missed work among their sample of TTH sufferers: 25% of males and 39% of females reported missed work due to their headaches.
The proportions of subjects with CTTH and ETTH who report lost and reduced-effectiveness days were similar: 12% of CTTH sufferers reported lost workdays and 47% reported reduced-effectiveness days. Sufferers of CTTH reported more frequently lost workdays and reduced-effectiveness days in comparison with ETTH sufferers. Subjects with lost workdays reported an average of 27.4 lost workdays per person; subjects with reduced-effectiveness days reported approximately 20.4 reduced-effectiveness days per person.
Future Directions and Conclusions
For individuals with headache, particularly chronic headaches or migraine, the question remains: why do most of these individuals suffer while others exposed to the same factors do not develop migraine? The etiology of these conditions is in need of focused studies that use the best epidemiologic study methods, including rigorous case definition. Genetic studies will provide a set of clues that should prove helpful to the prevention and treatment of the disease. These studies will need to be expanded to not only affected families but also broader population-based studies or other innovative designs so that the genetic components can be identified, as well as the environmental features. In the future, descriptive epidemiology needs to give way to analytic epidemiology to identify risk factors, possible susceptibility genes, and factors that trigger episodes among people who suffer from migraine headaches.
Migraine has been studied far more often than tension-type headache. Future research should also seek to expand our understanding of the variation in tension-type headache prevalence among certain subgroups, as well as to heighten our awareness of the impact tension-type headache has on the individual and society.
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