Abstract
Stress has long been considered as a major factor influencing primary headache disorders. The stress–headache relationship is multifaceted. Stress is hypothesized to (a) precipitate and exacerbate individual headache episodes, (b) contribute to headache disorder onset, and (c) exacerbate headache disorder progression. The headache experience itself can serve as a stressor that impacts an individual’s health and well-being. While all of the stress and headache relationships are plausible, in many instances the empirical evidence supporting each of the links is limited.
The challenge in understanding the role of stress in headache stems in part from the ill-defined nature of stress. Stress can be conceptualized as an imbalance between the demands that are placed on the body and the ability to manage those demands (1). However, stress can also refer to the number and magnitude of events that serve as triggers, the physiological responses that are triggered by the event(s), an emotional state, or the inability to cope with the demands of the situation. The demands can be real or imagined and they can occur in anticipation of, during, or following a demanding event. In his transactional model of stress and coping, Richard Lazarus (2) explained that appraisal and coping are factors that account for the individual differences in response to stress events. The appraisal process involves the evaluation of the threatening nature of the triggering event, the controllability of the triggering event, and the perceived ability to cope considering the available coping resources.
There is not sufficient evidence to determine whether individuals with primary headache experience a greater number of life stressors or are more reactive to life stressors compared to those without headache (3). Also undetermined is whether the impact of stress on headache differs for migraine and tension-type headache. Given the complexity of the relationship between stress and headache, well-conducted studies are needed to establish a clearer empirical understanding of the pattern of the connections between stress in its various forms, and headache in its various diagnostic types.
Milde-Busch and colleagues (4) report on the association between stress and primary headache in a group of adolescents. Specifically, the study examined the relationship between headache diagnosis and type of self-reported stress. Stress was measured using an established measure (Trier Inventory of Chronic Stress, TICS), headache was diagnosed using the established headache classification system (ICHD-II), and adolescents were recruited using a school-based and not hospital-based approach. The TICS stress inventory assesses perceived stress across a number of dimensions that relate to high demand (e.g. school overload, social overload) and lack of need satisfaction (e.g. lack of social recognition, social isolation). Although the TICS does not directly tap an individual’s stress appraisal, it captures the appraisal process to some indirect extent. The inventory also assesses chronic worry and a global measure of chronic stress. As noted by the authors, few studies assess the appraisal process and typically measure stress by assessing external stressors. External stressors were partially assessed in this study by soliciting self-reported daily hours of leisure time and whether this time was sufficient for recreation, whether the student had a best friend and an intimate friend, and school-reported number of students in class.
The ICHD-II was used to diagnose migraine headache and tension-type headache and their associated subtypes. The investigators also measured headache frequency, severity and duration using global reports based on single items and not daily diaries. The sample was restricted to 10th and 11th grade students in 37 public grammar schools in a southern German city. In a school-based approach, over 1800 students were invited to report on the experience of headache in the last six months. The final sample included 213 children with no reported headache, 129 with migraine, 614 with tension-type headache, and 249 with coexisting migraine and tension-type headache.
Milde-Busch and colleagues (4) found that adolescents with headache reported higher levels of stress. The most interesting and main finding from the study was that adolescents diagnosed with migraine reported higher levels of all types of stress. More specifically, adolescents whose only diagnosed headache was migraine reported significantly higher T values for all TICS stress inventory dimensions. Adolescents with migraine plus tension-type headache reported higher T values in all stress dimensions, but with lower scores than individuals with pure migraine. For adolescents with tension-type headache only, increased T values were confined to just two dimensions, dissatisfaction with job and excessive school demands.
Milde-Busch and colleagues (4) note that their findings are not consistent with other studies that reported greater stressors in adolescents with coexisting migraine plus tension-type headache than in individuals with pure migraine. They also note that their findings are not consistent with other studies that reported stress experience in children with tension-type headache. The investigators suggest that methodological and sample differences in the different studies may account for the inconsistent findings. Although acknowledging that the pattern of results is open to interpretation, the investigators suggest that poorer appraisal and coping strategies may be present in individuals with pure migraine. They further suggest that adolescents with migraine may be more responsive than those with tension-type headache to behavioral treatment improving coping skills. The higher levels of perceived stress for adolescents with migraine were not accounted for by higher levels of external stressors, at least in the limited way external stress was assessed. Thus, it does not appear that adolescents with migraine had greater objective demands, but that they perceived their demands to be greater and were more affected by them. What was not reported in this study was whether individuals with migraine had higher levels of the headache frequency, severity and duration, and if so, whether that helped explain the higher levels of reported stress. Headache frequency, severity and duration were assessed but not reported for migraine. In a post hoc analysis for tension-type headache, the number of affected stress dimensions decreased with decreasing frequency of tension-type episodes. It would be interesting to know whether the relationship of stress and migraine results from the frequency, severity and duration of migraine or from some other aspect of the headache disorder.
The cross-sectional nature of the study limits the ability to clearly explain the findings or determine the direction of the effects. That is, whether the effect is unidirectional with stress contributing to headache or with headache contributing to stress, bidirectional with stress and headache independently affecting each other, or at least in some headache sufferers, whether there are shared factors at biological or other levels that are contributing to both migraine (or other headache) and poor coping and emotional sensitivity. Other study limitations, fully acknowledged by the investigators, include diagnosis not validated by physician diagnosis and the TICS not being validated for this age group. Other limitations to consider are that the TICS is not a specific measure of stress coping or appraisal and that there was not a more comprehensive assessment of daily hassles or major life events.
With so much assumed and relatively little empirically known about the stress and headache relationship, studies like the one conducted by Milde-Busch and colleagues (4) are important contributions. The investigators conducted a methodologically strong study that produced interesting findings, particularly that higher levels of stress are observed in adolescents with migraine, and not with tension-type headache, compared to adolescents without headache. Not surprisingly, the findings also leave a number of unanswered questions. Future studies can build on these results and replicate them in comparable samples of adolescents, in other countries, using other stress measures specific to the appraisal and coping process and level of external stressors. Studies will also be strengthened using a daily diary method and assessing the influence of headache frequency, severity and duration on reported stress. Until then, conclusions can be tempered on whether migraine patients might be more likely than tension-type headache to benefit from behavioral interventions designed to improve stress appraisal and coping strategies.