++
The prevalence of TTH has not been widely studied. Among published
studies of TTH that use the 1988 IHS criteria, the 1-year period
prevalence ranges between 14.35 and 93.02 for
ETTH, and 0.05,33 and 8.133 for
CTTH (Table 17-6). Variation in prevalence estimates may be due,
in part, to differences in study methodology. Lifetime prevalences
are higher than 1-year period prevalences. The age distribution
of the population studied influences prevalence estimates. Case
definition also plays a role. Studies of the epidemiology of TTH
use various levels of diagnostic specificity. Although some studies
group all TTH (IHS 2.0) subjects together, other studies distinguish
between subjects with ETTH, (IHS 2.1), CTTH (IHS 2.2), and headache
of the tension-type fulfilling all criteria except one (IHS 2.3).
Prevalence estimates may also vary because of differences in the diagnostic
sensitivity and specificity of the methods used to collect symptom
data. Methods of data collection (e.g., self-administered questionnaires,
telephone interviews, and clinical examinations) as well as the
quality of data collection may influence levels of diagnostic accuracy. Finally,
the source of the study population, community based or clinic based,
is likely to cause varying prevalence estimates. A meta-analysis
might help explain how much each of these factors contributes to
the variation in prevalence among studies. Following is a summary
of several TTH studies that used the IHS criteria.
++
++
Schwartz and colleagues8 conducted the only
large-scale population survey in the United States describing the
epidemiology of ETTH and CTTH, as defined by the IHS criteria. These
investigators used data from a telephone survey of 13,345 residents
of the Baltimore County, Maryland, area32 to estimate
the 1-year period prevalence of ETTH and CTTH by sex, age, education,
and race. They found that the overall prevalence of ETTH in the
past year was 38.3%.
++
Lavados and colleagues5 interviewed a representative
sample of 1,385 adults (<14 years old) in Santiago, Chile, using
an in-person interview. Subjects reported details about the type
of headache from which they suffered most often. The 1-year prevalence
of ETTH was 24.3%. The lower prevalence in this study compared
with that of Schwartz and colleagues8 may be explained
by the case definition used by the Lavados group. Cases were only
identified if TTH was the most common headache. When Schwartz and
colleagues8 used similar criteria, they found an
ETTH prevalence of 25.3% compared with 38.3% after
the second headache type was classified.
++
Rasmussen and colleagues,2 on the other hand,
reported ETTH prevalence estimates that are higher than those of
most other studies (see Table 17-5). In this study, potential participants
were identified from the Danish National Central Person Registry
and invited to a general health examination, with an emphasis on
headache. Of the 1,000 potential study subjects, 740 males and females
participated in the study. The 1-year period prevalence of ETTH
was estimated to be 74.0%. The prevalence of ETTH may be
higher in this study because of the way in which the invitation
was worded. Because potential subjects were invited to a health
examination with an emphasis on headache, individuals who had headaches
may have been more likely to participate. Thus, there may have been
an over-representation of headache sufferers among the participants.
++
The prevalence of CTTH is markedly lower than that of ETTH. Schwartz
and colleagues8 found that the overall prevalence
of CTTH was 2.2%. Tekle-Haimanot,33 Lavados,5 and
Castillo and their colleagues62 reported similar
estimates of 1.7%, 2.6%, and 2.2%, respectively,
among the subjects they studied.
+++
Prevalence by
Demographic Features
++
The prevalences of both ETTH and CTTH vary by age, gender, race,
and educational level. TTH is slightly more common among females
than males. Schwartz and colleagues8 found that
women had a higher prevalence of ETTH than men (men, 36.3; women,
42.0), with an overall prevalence ratio of 1.16 to 1.0. The female
preponderance occurred at all age, race, and educational levels.
Several other studies also report a higher prevalence of TTH among
women,2–7 with female-to-male gender ratios
ranging from 1.252 to 1.9.5
++
Similarly, the prevalence of CTTH is also higher among females
than males. In the study published by Schwartz and colleagues,8 the
prevalence was 2.8 in women and 1.4 in men, with an overall prevalence
ratio of 2.0. Studies reported by Tekle-Haimanot,33 Lavados,5 and
Castillo and their colleagues62 also reported higher
prevalence among women than men.
++
The prevalence of TTH varies by age. Prevalence peaks in the
thirties and forties, with a decline thereafter.3,5,8 Pryse-Philips
and colleagues6 reported a similar, although slightly
earlier, peak prevalence in the 25- to 34-year-old age group. Rasmussen
and colleagues,2 on the other hand, found that
the prevalence of TTH decreased with increasing age, and Gobel and
colleagues38 found no difference in prevalence
by age. The lack of association reported by Gobel and colleagues
may be attributed to the use of very wide age intervals; whereas
in most studies age is categorized into 10-year intervals,2,3,5,6,8 Gobel
and colleagues used 20-year age groupings.
++
Tekle-Haimanot,33 Lavados,5 and
Schwartz and colleagues8 all reported an increase
in the prevalence of CTTH with increasing age. This may be explained
by the hypothesis that in some individuals, ETTH develops into a
chronic form over a prolonged period of time.17,69 Gobel
and colleagues38 did not find any difference in
the prevalence of CTTH by age, but again this may be attributed
to the use of very wide age intervals.
+++
Prevalence by
Geographic Region and Race
++
Some of the observed variation in the prevalence of TTH among
studies may be the result of racial or ethnic differences. Each
of the reported studies of the epidemiology of TTH using the IHS
criteria was conducted in a different country, and based on these
results, prevalence appears to be highest in the western hemisphere5,6,8 and
Denmark,2 and lowest in the Asian countries.3
++
The only published study of TTH using the IHS criteria that reported
the prevalence of TTH by race was that of Schwartz and colleagues.8 In
this study, the prevalence of ETTH was significantly higher in whites
than in African Americans in both men (40.1% versus 22.8%)
and in women (46.8% versus 30.9%). The prevalence
of CTTH by race paralleled that observed for ETTH: prevalence was
higher in whites than in African Americans in both men (1.6% versus
1.0%) and women (3.0% versus 2.2%).
+++
Prevalence by
Socioeconomic Status
++
The evidence regarding the relationship between socioeconomic
status and the prevalence of ETTH is mixed. Schwartz and colleagues8 reported
that the prevalence of ETTH increases with increasing educational
level, a measure of socioeconomic status. Prevalence peaked among
those with a graduate-level education (men, 48.5%; women,
48.9%). Lavados and colleagues5 found
a similar direct correlation between ETTH prevalence and socioeconomic
status. Other studies have not found this direct association.6,38 Gobel
and colleagues38 reported no significant differences
by education; however, their study used only two educational categories
(i.e., basic and secondary) and, as such, may simply lack the sensitivity
to detect patterns observed in other studies that used a greater
number of educational or income categories. It is also possible
that the influence of socioeconomic status varies by country.
++
The relationship between socioeconomic status and migraine may
differ for CTTH. Schwartz and colleagues8 and Lavados
and colleagues5 reported that the prevalence of
CTTH declines with increasing educational level, especially among
women. Gobel and colleagues38 found no association
between CTTH prevalence and educational level. Schwartz and colleagues8 suggested
that the epidemiology of CTTH, with its higher risk in women and
strong relationship to socioeconomic status, is intermediate between
that of ETTH and migraine and may reflect the progression of both
headache types to a chronic form.
+++
Headache Characteristics
++
Over 90% of subjects with ETTH report mild to moderate
headache pain intensity; attacks typically occur three times per
month.2,8,38 Lavados and colleagues5 found
that more than 86% of TTH sufferers report mild to moderate
pain that occurs three to four times per month. The headache frequency
reported by Lavados and colleagues is slightly higher than those
reported by Schwartz,8 Gobel,38 and
Rasmussen and their colleagues2 because the Lavados
sample included both ETTH and CTTH sufferers.
++
CTTH, on the other hand, is typically associated with higher
pain intensity and more frequent attacks. In one study, 86% of
subjects reported moderate or severe pain (moderate, 44%;
severe, 42%).38 Using a 10-point scale,
Schwartz and colleagues8 found significantly higher
pain intensity scores among CTTH subjects than ETTH subjects (CTTH,
5.55; ETTH, 4.98; P <.001).
For CTTH, headache frequency ranges from 15 to 30 headaches per
month.8,38
++
Certain clinical characteristics occur more frequently among
TTH sufferers, and these characteristics often differ by gender.
Lavados and colleagues5 reported that bilateral
pain occurs in the majority of TTH sufferers but occurs with even
greater frequency among women than men (men, 87.9%; women,
61.1%; P <.01). Throbbing
pain occurs approximately equally in 66.4% of men and 56.8% of
women; this feature, often viewed as a hallmark of migraine, does
not discriminate the two disorders. These investigators also found
that many TTH subjects report pain that is exacerbated with movement
(men, 69.8%, women, 75.5%; P = .4),
which is surprising because pain that is exacerbated by movement
is normally associated with migraine rather than TTH. Pressing pain,
photophobia, and phonophobia were also frequently reported: each
of these characteristics occurred significantly more often among
women than men. Nausea was not commonly reported by any of the study
participants.
++
Rasmussen58 reported the first population-based
study to examine work loss data in ETTH. Of the employed participants
with ETTH, 12% reported being absent from work at least
once during the previous year because of ETTH. Among those who reported
lost workdays, the majority (68%) were absent from 1 to
7 days during the previous year, 25% were absent between
8 and 14 days during the year, and only 16% were absent
more than 14 days during the previous year.
++
In their survey of Baltimore County residents,8 Schwartz
and colleagues also measured the impact of headache in the workplace.59 In
this study, reduced ability to function and an 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
the result of ETTH.59
++
Schwartz and colleagues8 also reported that
among subjects with ETTH, 8.3% reported missed workdays,
while 43.6% reported reduced effectiveness days because
of headache. Among those with missed workdays, an average of 8.9
missed workdays were reported, whereas subjects with reduced effectiveness
days reported approximately 5.0 reduced effectiveness days per person.
++
Lavados and colleagues5 found higher levels
of missed work among their sample of TTH sufferers: 25% of
males and 38.9% of females reported missed work because
of their headaches. They also found that TTH sufferers were likely
to miss family and social activities as a result of their headaches.
Approximately 27.6% of males and 25.3% of females
missed family or social activities because of their headaches.
++
In the Schwartz8 study, the proportions of CTTH
subjects reporting lost and reduced effectiveness days were similar
to those reported by ETTH subjects: 11.8% of CTTH sufferers
reported lost workdays, and 46.5% reported reduced effectiveness
days. However, in contrast with the ETTH sufferers, CTTH sufferers
reported more frequent lost workdays and reduced effectiveness days.
Subjects with lost workdays reported an average of 27.4 lost workdays
per person, whereas subjects with reduced effectiveness days reported
approximately 20.4 reduced effectiveness days per person.