Abstract
Migraine and tension-type headache (TTH) are often viewed as distinct entities and defined as such in the International Classification of Headache Disorders, 2nd edition (ICHD-II) criteria, although there is also empirical evidence to suggest they may be etiologically similar. This study aims to investigate whether migraine and TTH are etiologically related conditions. First, we explored whether migraine and TTH were associated with the same environmental and lifestyle risk factors at the population level. Second, we examined comorbidity of migraine and TTH in a twin design. By comparing the associations in monozygotic (MZ) and dizygotic (DZ) twin pairs, we investigated whether the comorbidity can be explained by genetic factors that influence both conditions. Results indicated that migraine and TTH were largely associated with the same environmental and lifestyle factors, including younger age, female sex, higher body mass index, more depression, stress at home, and less participation in regular exercise, with consistently stronger effects for migraine than for TTH. Migraine in one twin was significantly associated with TTH in the other twin. A stronger cross-trait, cross-twin association in MZ than DZ twins suggested that this comorbidity may also be partly due to shared genetic factors, although the difference in associations was not significant. In conclusion, our findings are consistent with the hypothesis that migraine and TTH have partly shared etiologies. For both treatment and research, it may be advisable not to make a rigid distinction, but to treat migraine and TTH as related conditions.
Highlights
Migraine and tension-type headache (TTH) are often viewed as distinct entities and defined as such in the International Classification of Headache Disorders, 2nd edition (ICHD-II) criteria, there is empirical evidence to suggest they may be etiologically similar
The International Classification of Headache Disorders (ICHD) criteria have always classified these two conditions as distinct entities that are mutually exclusive in terms of symptoms: essentially, the diagnostic criteria for TTH are the negation of those for migraine; for example, not bilateral, non-pulsating, and not aggravated by physical activity (Headache Classification Committee of the International Headache Society, 1988, 2004, 2013)
TTH patients are typically excluded from genomewide association (GWA) studies, based on the assumption that TTH is genetically different from migraine
Summary
Migraine and tension-type headache (TTH) are often viewed as distinct entities and defined as such in the International Classification of Headache Disorders, 2nd edition (ICHD-II) criteria, there is empirical evidence to suggest they may be etiologically similar. A migraine attack may include symptoms of TTH and vice versa, and many patients experience attacks of both types (Kaniecki, 2002), suggesting a fair amount of comorbidity between the two conditions. A Danish population study by Ulrich et al (1996) reported that the 1-year prevalence and sex ratio of TTH did not differ in individuals with and without migraine, suggesting they are independent conditions. Since large sample sizes are essential in gene-finding studies, this question is of importance
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