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Impact of chronic headache on workdays, unemployment and disutility in the general population
  1. Espen Saxhaug Kristoffersen1,2,3,
  2. Knut Stavem4,5,6,
  3. Christofer Lundqvist1,4,6,3,
  4. Michael Bjørn Russell1,4
  1. 1 Head and Neck Research Group, Research Centre, Akershus Universitetssykehus HF, Lorenskog, Norway
  2. 2 Department of General Practice, HELSAM, University of Oslo, Oslo, Norway
  3. 3 Department of Neurology, Akershus University Hospital, Lorenskog, Norway
  4. 4 Institute of Clinical Medicine, Campus Akershus University Hospital, University of Oslo, Oslo, Norway
  5. 5 Department of Pulmonary Medicine, Medical Division, Akershus University Hospital, Lorenskog, Norway
  6. 6 HØKH, Research Centre, Akershus University Hospital, Lørenskog, Norway
  1. Correspondence to Espen Saxhaug Kristoffersen, Head and Neck Research Group, Research Centre, Akershus University hospital, Lørenskog, Norway; e.s.kristoffersen{at}medisin.uio.no

Abstract

Background Data on the socioeconomic burden of chronic headache (≥15 days/last month or >180 days/year) is lacking. This study investigated the impact of chronic headache on sickness absence, unemployment and disutility in the general population in Norway.

Methods 30 000 persons aged 30–44 from the general population were screened for chronic headache by a screening questionnaire. The responder rate was 71%. The International Classification of Headache Disorders was used. We analysed the association of chronic headache with lost workdays, days with ≥50% reduced productivity, sick leave, unemployment and disutility, as assessed with the Short-Form Six-Dimension (SF-6D) in separate regression analyses.

Results Eighty-three per cent (427/516, 79% women) of the eligible participants completed the data on workdays and utility. They reported a mean of 9.7 (SD 24.8) workdays lost over the last 3 months, because of headache. The mean disutility score (1-SF-6D score) was 0.41. Thirty-three per cent were on long-term (>1 year) sick leave. The OR for being on sick leave was 1.9 (95% CI 1.1 to 3.2, p=0.017) for those with secondary compared with primary chronic headache. Similarly, the OR for increased number of workdays lost to headache was 3.5 (95% CI 1.8 to 6.5, p<0.001) and for unemployment 1.7 (95% CI 1.0 to 2.9, p=0.07), for those with secondary compared with primary chronic headache. Secondary chronic headache, high headache frequency and high psychological distress were significantly associated with higher disutility score.

Conclusions The burden of chronic headache in the general population is substantial with high rates of lost workdays and disutility.

  • epidemiology
  • sickness absence
  • general practice

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Introduction

Headaches are among the world’s top 10 leading causes of disability and a public health problem.1 2 In the European Union (EU), the total annual direct and indirect cost for headache is €173 billion, and headache is one of the most costly neurological disorders.3 Most headaches are self-treated in the community or by a general practitioner (GP) in primary care.4 However, data on the burden of headache disorders in the general population is limited, and even less is known for chronic headaches (ie, ≥15 days/last month or ≥180 days/year).2 Because chronic headache has a prevalence of 3%–4% and affects people in their most productive phase of life, it leads to activity limitation, work absence and social burden for individuals, families, health services and welfare systems.2 3 5–7 Reduced productivity and sickness absence are the two main contributors to the indirect costs, accounting for over 90% of the total costs of headache disorders.2 3 The aims of this study were to determine the impact of chronic headache on lost workdays, reduced productivity, sick leave, unemployment and disutility in the Norwegian general population.

Methods

Study design, population and variables

This was a cross-sectional epidemiological survey of 30 000 representative persons aged 30–44 drawn from the general population of eastern Akershus County, Norway.6 7 When the sample was drawn in 2005, the total population of the sampling area was 338 670, which was 7.4% of the total Norwegian population. The sample represented 36.6% of those aged 30–44 in the eastern municipalities of Akershus County and 2.9% of this age group in Norway. Data from Statistics Norway suggested that the sampling area was representative for the total Norwegian population regarding age, sex and marital status. People with employment within trade, hotel/restaurant and transport were over-represented, while those in industry, oil and gas and financial services were under-represented in the sampling area compared with the total Norwegian population.6 7 A postal questionnaire was used to screen for possible chronic headache (≥15 days/last month and/or ≥180 days/last year); two postal reminders were sent to non-respondents.

Seventy-one per cent (20 598/28 871) of the study population responded to the screening questionnaire. The Norwegian Data Services prohibited further contact with the non-participants. Thus, no information about the non-respondents to the screening questionnaire exist.

Screening-positive subjects were invited to a clinical interview at Akershus University Hospital. Those invited were offered examinations during daytime, in the late afternoon or in the evening. When a participant failed to appear several times or was not able to come to the headache research centre, a telephone interview was offered. The phone calls were made both in the morning, in the middle of the day, in the afternoon and in the evening and on different days. Those not reached after at least six phone calls were regarded as non-participants. Of 935 patients with self-reported chronic headache, 633 participated in clinical interviews (490 as an ambulatory visit, 143 by telephone) by two headache experts (figure 1 online only).6 7 The only exclusion criterion was insufficient Norwegian language skills to participate in a headache interview.

Figure 1

Flow chart of the study (online only).

The participants filled in a self-administered questionnaire that included information on sociodemographics, height, weight, smoking status, medication overuse, headache frequency, utility (Short-Form Six-Dimensions (SF-6D) derived from Short-Form-36 (SF-36)), headache disability (The Migraine Disability Assessment (MIDAS)) and psychological distress by Hopkins Symptom Checklist-25 (HSCL-25).8–10 Headache frequency was dichotomised as above the 75th percentile (≥80 days/3 months) or below. HSCL-25 explores the symptoms of depression and anxiety and is a validated tool for measuring the level of psychological distress as defined by HSCL-25 score (≥1.67 for men and ≥1.75 for women). The currency exchange rate was 1 NOK=0.1 Euro at the time of the study.

Employment status, sick leave, lost workdays and reduced productivity at work

Employment status ((1) yes or no, (2) part time or full) and sick leave ((1) yes or no, (2) type of sick leave) were based on self-reports.

All participants were asked about number of lost workdays during the last 4 weeks and how many of these lost workdays were due to headache. Furthermore, the participants responded to two items from the MIDAS questionnaire8: (1) ‘How many days in the last 3 months did you miss work or school because of your headaches?’ (2) ‘How many days in the last 3 months was your productivity at work or school reduced by half or more because of your headaches? (Do not include days you counted in question one where you missed work or school)’ . If the participants did not work for other reasons than headache, they thus scored 0 lost workdays.

SF-6D preference scores

The SF-6D preference-based index comprises 11 items from the SF-36 questionnaire that were revised into a six-dimensional health state classification system.10 The six dimensions are physical functioning, role limitations, social functioning, pain, mental health and vitality. The SF-6D items are aggregated into a utility score based on an algorithm derived from preferences for health states of the general UK population using the standard gamble method.11 It reflects a continuous outcome scored on a 0.29–1.00 scale, with 0 representing dead and 1.00 indicating full health.11 The SF-6D score was calculated based on the Norwegian SF-36 (V.2), using published algorithms.12 The utility loss is presented as disutility scores (ie, 1-SF-6D).

Headache classification

The International Classification of Headache Disorders (ICHD-II) was used in the interview. The diagnoses were later reclassified according to ICHD-III.13 Chronic headache was defined as headache ≥15 days/months for at least 3 months or ≥180 days/year.

Those with medication overuse, but no other known secondary cause of chronic headache, were included as primary chronic headaches. Cervicogenic headache (CEH) was classified according to the criteria of the Cervicogenic Headache International Study Group, requiring at least three criteria to be fulfilled, not including blockade of the neck.14 There was a diagnostic overlap between people with chronic post-traumatic headache (CPTH) and CEH, and the two groups were merged for the purpose of statistical analyses.

Headache attributed to chronic rhinosinusitis (HACRS) was defined by headache >14 days/month and the rhinosinusitis criteria established by the American Academy of Otolaryngology–Head and Neck Surgery published in 2003, adding that the symptoms had persisted for ≥12 weeks.15 All subjects diagnosed with CEH or HACRS in the present study fulfil the new ICHD-III criteria for these chronic headaches.13

Statistical analysis

For descriptive data, proportions, mean (SD) or median (25th–75th percentile) are given. Groups were compared using the t-test (continuous data) or the Χ2 test (categorical data).

We used logistic regression models to evaluate unemployment and sick leave (yes or no, as the dependent variable) in people with chronic headache, using multivariable models. The models were adjusted for age (age/10), sex, education, time since headache onset (year/10), migraine status (yes or no), medication overuse (yes or no), headache frequency and psychological distress (yes or no). All the independent variables were forced into the models. The results are presented as ORs with 95% CIs.

A binomial fractional logit regression model, with robust variance estimator, was fitted to investigate factors associated with lost workdays (as a proportion of a maximum of 90 days) as the dependent variable, adjusting for the same variables as above. The results are presented as ORs with 95% CIs.

A multivariable linear regression model was used to evaluate utility loss (ie, 1-utility as the dependent variable), again forcing the same adjustment variables into the model.

Significance levels were set at p<0.05, using two-sided tests. We used Stata V.14.2for all statistical analyses.

Ethical issues

The Regional Committee for Medical Research Ethics and the Norwegian Social Science Data Services approved the study. All participants gave informed consent.

Results

In total, 427 of the 516 eligible participants (83%) completed the self-administered questionnaire. Respondents and non-respondents were not significantly different (table 1). Of the participants, 331 had primary and 96 had secondary chronic headache. Among the participants with primary chronic headache, three people had new daily persistent headache, while among those with secondary chronic headache seven people had other secondary chronic headaches (ie, one had overlap post-traumatic/HACRS, three had persistent headache attributed to craniotomy (ICHD code 5.6), one had post-meningitis headache (ICHD code 9.1.1.2), one had developed a chronic headache after diving (ICHD 10.1.3) and one had developed headache >3 months related to pre-eclampsia (ICHD code 10.3.4). These 10 people were included in the regression analyses. More baseline characteristics are given in tables 1 and 2.

Table 1

Descriptive data for respondents and non-respondents with chronic headache

Table 2

Descriptive data for participants with chronic headache

The distributions of workdays lost and days with ≥50% reduced productivity due to headache were skewed. The median number of full workdays lost due to headache was 0 (25th–75th percentile 0–2), and median number of days with ≥50% reduced productivity at work due to headache was 0 (25th–75th percentile 0–10) in the last 3 months. The corresponding mean numbers were 9.7 (SD 24.8) and 7.5 (SD 13.4). Thirty-three per cent (n=139) were on long-term (>1 year) sick leave, and 8% (n=35) were on sick leave <1 year. Among those with lost workdays during the last 3 months, the mean and median number of workdays lost was 29.0 (SD 35.9) and 8 (25th–75th percentile 2–63), respectively. Excluding the people on sick leave >1 year gave mean lost workdays of 5.4 (SD 16.8) in the last 3 months. There were no significant differences between those with and without other chronic pain regarding lost workdays or days with ≥50% reduced productivity due to headache.

Less than 30% had higher education, and there was no association between education level and age at onset of headache. Thirty-one per cent were unemployed. For a more detailed breakdown of socioeconomic variables, see table 2.

In multivariable logistic regression analysis, patients with secondary chronic headache had higher odds of being on sick leave than those with primary chronic headache, and female gender, low education and high psychological distress were associated with higher odds of being unemployed and on sick leave compared with the respective reference categories (table 3).

Table 3

Multivariable logistic regression analysis with variables associated with unemployment (n=399) and sick leave (n=400) at the time of the interview

Having secondary chronic headache or a high headache frequency significantly increased the odds of having lost workdays due to headache in the binomial fraction regression analysis. Having psychological distress was associated with having workdays with ≥50% lost productivity (table 4).

Table 4

Variables associated with lost workdays (n=376) and workdays with >50% reduced productivity (n=370) due to headache last 3 months

Secondary chronic headache was associated with higher disutility than primary chronic headache. Also, having a high headache frequency or psychological distress was associated with increased disutility in the multivariable linear regression model (table 5).

Table 5

Multiple linear regression analysis with variables associated with utility loss (disutility) based on Short-Form-Six Dimension (n=392)

Discussion

In this large population-based study, almost one-third of the respondents had long-term sick leave (>1 year). Secondary chronic headache, female gender and/or high psychological distress were associated with high sickness absence in multivariable analysis. Furthermore, high headache frequency and/or high psychological distress were the two main predictors for number of lost workdays and disutility.

Some methodological considerations should be noted. The size of the population-based sample in the present study and the high response rate should ensure its representativity.6

The recipients of the screening questionnaire were informed that we investigated headache, but not informed about the focus being chronic headache. It is possible that health-related questions receive more interest from those suffering from this specific health issue. To avoid a selection bias related to available time for interviews during day time (which may be related to sick leave or unemployment), the interviewers were very flexible in the planning of the timing of the interviews, including evenings.

The 30–44 years age range in our study was chosen in order to avoid major age-related comorbidity of non-headache disorders, at the same time as these years are among the most productive years for most people. We cannot exclude that our findings may differ in younger and older people. Most of the people in this population sample did not have specific chronic headache treatment or significant comorbidity, in contrast to what would be expected in headache clinics. Face-to-face interviews, as in the present study, provide more valid headache diagnoses than questionnaire-based studies.16 A challenge to study headaches attributed to sinus disease is the lack of uniform diagnostic criteria. The ICHD-II did not accept chronic rhinosinusitis as a cause of headache unless relapsing into an acute stage, and we feel the new ICHD-III criteria are too little specific compared with criteria established by the American Academy of Otolaryngology–Head and Neck Surgery.13 It has been suggested that also these former clinical criteria of HACRS may be suboptimal for research purposes.13 We did not include a CT scan in the diagnostic setup in this population-based study due to the feasibility, practical and potential ethical problems of imaging many hundred participants without a clear reason. However, it should be emphasised that all subjects diagnosed with HACRS in the present study fulfil the new ICHD-III criteria.

The overall sample size limited the number of variables that could be analysed as potential confounders. We did not include a control group of people without headache or with episodic headache, and thus, some of the comparisons of are made with historical population data from Statistics Norway.

The data on sick leave were based on self-reports and therefore open to recall bias, but we think the detailed clinical interviews most likely reduced such bias. Furthermore, people tend to systematically under-report negative outcomes in order to give a more favourable impression.17 18 Therefore, we think the present data based on a sample recruited from the general population is a conservative estimate of the number of workdays lost to headache. It may be suggested that data from official registries are more likely to be unbiased than self-reported data. However, in the official Norwegian sick leave registry, there is a well-known problem with validity and specificity of the GPs’ diagnostic coding system (ICPC-II) when used as a stand-alone classification.19 Some authors advocate the use of sickness absence periods instead of lost workdays due to the often skewed distribution of days. We did not collect such period data, but we report both mean and median lost workdays in addition to the proportion with short-term or long-term sick leave.

Sociodemographic differences in education, partnership, employment, income and type of work are all known to interfere independently with headache frequency and sickness absence.20–22 However, these variables are correlated, and only the highest attained educational level was available for use in the present study.

Finally, the cross-sectional design in the present study does not permit any conclusions about direction of causality or associations.

The proportion of chronic headache sufferers with long-term sick leave (>1 year) was higher in this study than in the general Norwegian population, where approximately 10% are on sick leave >1 year.23 In the present study, those with psychological problems had the highest sick leave, which supports previous finding that psychological problems and chronic pain account for a high proportion of sick leave.22 24 25

It is possible that an improvement in headache frequency may improve psychological distress or vice versa. Independently of the causal directions of these associations, it is important always to take psychological factors and comorbidities into account when treating headache. Thus, a best possible treatment approach for many headache sufferers includes acute and prophylactic medications together with multidisciplinary treatment addressing illness perception and psychological distress. This again, may improve productivity, frequency of sick leave and disutility and should be addressed in future studies.

The present study also supports another general population study reporting that being female and having a headache frequency >14 days/month was associated with increased odds of sick leave, and more so if there was co-existing musculoskeletal pain and depression/anxiety.22 The proportion of respondents with sick leave was higher and on average more workdays were lost to headache in the present study than in the other study, which was based on self-reported questionnaire diagnoses and did not ask specifically about workdays lost to headache.22

In the present study, the participants tended to attend work despite their chronic headache, as they had approximately as many days with 50% reduced productivity as actual missed workdays. This supports previous reports that many headache sufferers still go to work even if they wake up with headache and continue their work if their headache comes during the working time.26 27 Having a high rate of short-term sickness absence, such as repeated single days or more continuous periods, may be an important and possibly modifiable risk factor for ending up permanently outside the labour market.28

The data reported here suggests that chronic headache is associated with considerable burden to the individual and potential loss to society through reduced work productivity. This is a new finding, which has previously not been reported on patients with criteria-defined chronic headache from the general population. These findings may have large economic implications and are important for healthcare policies. Furthermore, it supports that neurological disorders are major contributors to disability and costs for the society.

The overall costs to society due to headache are difficult to estimate, especially since indirect costs may contribute as much as 90% of the costs.3 Furthermore, productivity loss is difficult to ascertain, and exact cost calculations based on our data would be associated with large uncertainty. In economic evaluation, how to account for productivity loss is controversial,29 and approaches differ between settings and countries.30 For these reasons, we have avoided cost calculations.

Those with secondary chronic headache had clearly higher odds of workdays lost to headache than those with primary chronic headache. This suggests that secondary headaches are more disabling, often more frequent and may have less effective treatment options than primary headaches.7

Furthermore, low education, co-occurrence of high psychological distress and a high headache frequency were positively associated with sick leave and/or increased number of workdays lost to headache, in accordance with previous reports.20–22 24 The proportions of chronic headache sufferers with maximal attained education >15 years and employment were lower in this study, than in the general Norwegian population, where approximately 40% have higher education and 86% are employed.23 This confirms the association of low socioeconomic status and frequent headache from other studies with less precise questionnaire-based diagnosis and further underlines the complex total burden that people with chronic headache suffer from.20 21

The estimated SF-6D utility scores can be used in calculations of quality-adjusted life years in economic evaluation.11 Such a utility loss has previously not been presented for patients with chronic headaches. Overall, the average utility loss (1-SF-6D score) was 0.41, which is considerable compared with the general population, for example, a US general population aged 35–44 years that had a disutility of 0.20.31 The disutility was larger for those with a high headache frequency or co-occurrence of psychological distress, in line with previous studies of chronic pain.32 The utility loss also was comparable to patients with other chronic diseases, such as chronic obstructive pulmonary diseases, coronary heart diseases and diabetes mellitus.33–35

In conclusion, chronic headache was associated with a high proportion of lost workdays, reduced work productivity and high utility loss in the general population.

What is already known on this subject

  • Chronic headache (headache >15 days/month) is a common public health problem with an estimated prevalence of 3%–4% in the general population.

  • Knowledge of the socioeconomic burden of chronic headache in the general population and community is lacking.

  • The few other studies on the subject are from specialised care with highly selected populations with a focus on (mostly episodic) migraine or based on less precise and less valid questionnaire-based diagnosis.

What this study adds

  • This is the first epidemiological study with thoroughly classified headache to analyse the impact of chronic headache on work productivity, lost workdays, sick leave and disutility.

  • The study highlights the large consequences as chronic headache in the general population is associated with considerable burden to the individual and potential loss to society through reduced work productivity, sickness absence and disutility.

Acknowledgments

The authors would like to thank Kjersti Aaseth and Ragnhild Berling Grande for conducting the clinical interviews.

References

Footnotes

  • Contributors MBR had the original idea for the study and planned the overall design together with CL. ESK and KS conducted the data analysis. ESK prepared the initial draft. All authors were involved in the planning and interpretation of the data analysis and have commented on, revised and approved the final manuscript.

  • Funding This study was supported by grants from the South East Norway Regional Health Authority and Institute of Clinical Medicine, Campus Akershus University Hospital, University of Oslo.

  • Competing interests None declared.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.