Somatic symptoms beyond those related to a whiplash injury are increased in chronic whiplash: The Hordaland Health Study (HUSK)

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1 Somatic symptoms beyond those related to a whiplash injury are increased in chronic whiplash: The Hordaland Health Study (HUSK) Solbjørg Makalani Myrtveit 1, Jens Christoffer Skogen 2, Hanne Gro Wenzel 3, Arnstein Mykletun 2,4 1 Faculty of medicine and dentistry, University of Bergen (UoB), 2 Research Unit on Mental Health Epidemiology, Department of Health Promotion and Development, Faculty of Psychology, UoB, 3 Division of Psychiatry, St Olav University Hospital, Norwegian University of Science and Technology, 4 Norwegian Institute of Public Health, Division of Mental Health, Department of Public Mental Health, Bergen, Norway Corresponding author: Arnstein Mykletun, director of department, professor Department of Public Mental Health Norwegian Institute of Public Health arnstein.mykletun@iuh.uib.no Word count: 3,506 Page count: 24 Number of tables: 3 Number of figures: 2 Declaration of interest: None Authors contributions: Authors Myrtveit, Skogen and Mykletun designed the study, while Wenzel contributed further to the scope of the study. Myrtveit conducted literature searches, and provided summaries of previous research. Myrtveit conducted the statistical analysis under the supervision of Skogen and Mykletun. All of the authors contributed to the interpretation of the findings, and Myrtveit wrote the first draft of the manuscript. All authors contributed to further refinement of the first draft, and have approved the final manuscript. Acknowledgements and Funding: The first author received a summer research grant from Uni Rokkan Centre. 1

2 Abstract Study design: Cross-sectional study Background: Chronic whiplash leads to considerable patient suffering, and to substantial societal costs. There are two competing hypothesis on chronic whiplash. The traditional organic hypothesis considers chronic whiplash and related symptoms to be a result of a specific injury. In opposition is the hypothesis that whiplash is a functional somatic syndrome, and related symptoms a result of society-induced expectations and amplification of symptoms. As expected, patients reporting chronic whiplash have more neck pain, headache and symptoms of anxiety and depression than the general population. Increased prevalence of somatic symptoms beyond those directly related to a whiplash neck injury is less investigated. In the perspective of chronic whiplash potentially being a functional somatic syndrome, it is particularly interesting to examine if chronic whiplash is associated with somatic symptoms as seen in somatization disorder. Therefore, we aimed to test the hypothesis that somatic symptoms seen in somatization disorder, and beyond those directly related to a whiplash neck injury, are increased in individuals self-reporting chronic whiplash. Methods: Data from the Norwegian population-based Hordaland Health Study (HUSK, ); N=13986 aged was employed. Chronic whiplash was self-reported by 403 individuals (2.9%). Using a list of 17 somatic symptoms arising from different body parts and organ systems and derived from the research criteria for somatization disorder (ICD-10, F45), the frequencies of somatic symptoms were compared between individuals reporting whiplash and individuals reporting no whiplash. Both participants in the health study and the staff collecting the data were blinded to the hypothesis of this study. Results: Chronic whiplash was associated with an increased level of all 17 somatic symptoms investigated (p<0.05). The association was moderately strong (group difference of 0.60 standard deviation), and only partly accounted for by confounding. Recent whiplash was more commonly reported than whiplash-injury a long time ago, and the association of interest weakly increased with time since whiplash (r=0.016, p=0.032). 2

3 Conclusions: The increased prevalence of somatic symptoms beyond symptoms expected according to the organic injury model for chronic whiplash, challenges the standard injury model for whiplash, and is indicative evidence of chronic whiplash being a functional somatic syndrome. 3

4 Introduction The term whiplash was first introduced in 1928 [1], describing the lash-like effect caused by sudden acceleration-deceleration forces acting on neck and upper trunk, mainly following a rear impact [2]. The incidence of whiplash has in most western countries been estimated to 4 per 1000 inhabitants [3], and is thought to be increasing [2, 4, 5] alongside increased traffic worldwide. The disorder leads to considerable short and long term patient-suffering [6-14], and to substantial societal costs [15, 16]. During the first months after acute neck injury, most patients recover rapidly [4, 17]. After 3 months, however, recovery seems to level off [18], and despite examinations revealing no neck changes, a substantial amount of patients remain symptomatic [19, 20]. Estimates on the transition from acute whiplash to chronic whiplash, defined as symptoms still seen after 6 months [21, 22], vary between 6% and 18% [2, 3]. Currently, there are two competing hypothesis on chronic whiplash. Some consider chronic whiplash an organic disorder with chronic pain due to injuries in the neck [17]. Others claim that the most appropriate is to consider chronic whiplash one of many functional somatic syndromes [23-25]. Functional somatic syndromes are characterized by medically unexplained symptoms and suffering [24, 26]. The symptoms reported by individuals with functional somatic syndromes are prevalent in healthy populations[27, 28] and characterized by diffuse and non-specific symptoms emerging from different organs/body parts [24, 26, 28-30]. Furthermore, the symptoms of functional somatic syndromes are very similar to somatization disorder, and the two conditions are thought to be closely related [24, 31, 32]. The organic and the functional models for chronic whiplash have different implications both concerning risk factors, prognostic factors and treatment, emphasizing the importance of studying chronic whiplash to determine which model better fits clinical evidence. Many questions regarding the underlying mechanisms, course and prognosis of whiplash remain unanswered [2, 6, 12, 33, 34]. For instance, there seems to be no direct relationship between the biomechanical forces involved in the whiplash trauma, the resulting tissue damage and the subsequently reported symptoms and functional capacity [2, 12, 18, 35, 36]. This might support the functional hypothesis. Patients with chronic whiplash report more symptoms of anxiety and depression than the general population [23, 37, 38], and they report the disorder to negatively affect their ability to work and reduce their quality of life [2, 11]. Studies have also concluded that these patients suffer from elevated levels of somatic symptoms [8-10, 12, 13], such as head and 4

5 neck pain. There are also some reports of increased frequency of symptoms not directly related to a whiplash neck injury [6, 8, 12, 23, 39], which are challenging to interpret according to the traditional injury model for chronic whiplash. Previous studies have investigated symptoms of whiplash patients [23], but studies exploring a broad range of somatic symptoms not directly related to a neck injury are lacking. We aimed to test the hypothesis that somatic symptoms beyond those directly related to a whiplash injury are generally increased in individuals self-reporting chronic whiplash, resembling the symptom profile of functional somatic syndromes. Furthermore, we aimed to examine if the proportion of the population self-reporting whiplash diminishes with time, and how the symptom burden changes with time since the whiplash injury. Materials and methods Study population Data from the Hordaland Health Study (HUSK) carried out in Hordaland County in Western Norway between 1997 and 1999 was used. This joint epidemiological research project was conducted in cooperation between the National Norwegian Health Screening Services, the University of Bergen and local health services. The base population included 29,400 individuals, born between 1953 and 1957, and therefore aged years upon participation. Of these, 18,565 (8,585 men and 9,980 women) accepted the invitation, filled in the questionnaires and attended clinical examinations including measures of blood pressure, height, weight, waist- and hip circumference. This resulted in a general participation rate of 63% (57% for men and 70% for women). For the purpose of the present study, we were interested in individuals reporting whiplash or no whiplash and their profile of somatic symptoms. Excluding everyone not answering the questions related to whiplash, questions on somatic symptoms and questions on covariates potentially associated with both exposure and outcome, left us with a study population of 13,986 individuals (75% of the HUSK participants; 2,756 excluded due to missing data on outcome and exposure and 1,823 excluded due to missing data on covariates). Exposure - whiplash As in previous studies [37, 40], self-reported incident whiplash was assessed using the question Have you ever experienced whiplash?, together with a follow-up question on how old the person was at the time of the injury. In correspondence with previous work [23], we 5

6 defined our group of chronic whiplash sufferers as individuals having experienced the trauma no sooner than one year prior to the survey and reporting neck pain for at least three consecutive months during the last year. This lead to an exclusion of individuals possibly still in their acute phase (first 6 months) of the disorder (N=11) and individuals reporting a whiplash trauma but not having developed chronic neck pain (N=33). This left us with a group of N=403 potential sufferers of chronic whiplash. Outcome - somatic symptoms The frequencies of common somatic symptoms arising from different body parts and organ systems were investigated. For this, a list of 17 somatic symptoms (abdominal pain, nausea, bloating, tongue plaque, regurgitation, frequent defecation, discomfort in genital region, skin discoloring, joint/muscle pain, dizziness, tiredness, paresthesia in extremities, burning eyes, headache, shortness of breath, chest pain and problems with urination) was used. The list contains 13 items from the ICD-10 research criteria for somatization disorder (F45) [31] and 4 other symptoms related to somatization and functional somatic syndromes [24, 26, 41]. It has previously been used when exploring somatization in relation to different disorders [42]. The participants were asked to indicate the frequency at which they experience each symptom by ticking off almost never, rarely, sometimes, often or almost always. In accordance with previous studies [42], the mean score for each individual was used as an indication of somatization tendency. Covariates Functional somatic syndromes, somatic symptoms and self-reported whiplash are related to a whole range of socio-demographic and health related factors [24, 25, 32, 41, 43-45]. We have therefore adjusted the association for the following factors: Gender was registered, as was marital status, grouped into not married, married, separated, divorced or widow/widower. Socioeconomic status was assessed trough questions on benefit recipiency and education. Participants were asked if they, at the time of participation, received any social aid or pension (Table 1). In relation to education, participants were grouped as having completed compulsory only, high school or university. The 133 not answering this question were set to compulsory only. As somatic diagnoses can affect the symptom profile, we are investigating the number of somatic illnesses each individual was suffering from at participation time, or had suffered 6

7 from earlier. The number of diagnoses was recorded as participants ticked off the following: heart infarction, angina pectoris, stroke, asthma, diabetes or multiple sclerosis. The responses from 18 participants reporting 3 or more somatic diagnosis were truncated to 3. Anxiety and depression were measured using the Hospital Anxiety and Depression Scale (HADS) [46]. HADS is a widely used self-report questionnaire considered reliable for patients in psychiatric and non-psychiatric settings, and for the general population [47-49]. The questionnaire consists of 14 readily understandable questions on symptoms, seven for depression (HADS-D) and seven for anxiety (HADS-A). Somatic symptoms commonly seen in anxiety and depression are excluded, making the scale useful in populations with somatic illness and symptoms. Each item has four alternative responses ranging from symptom not present (0) to maximum reported level of symptom (3), giving a sum score range from 0 to 21 for both subscales. In accordance with previous studies, a valid rating of depression and anxiety was defined as at least 5 completed items at each sub-scale (HADS-S and HADS-D) [49, 50], and the recommended cut-off score of 8 was used in the descriptive table [47-49]. Health-related behavior was evaluated in line with previous studies [51, 52]. The participants were asked Do you smoke cigarettes, cigars and/or pipe daily and grouped as smokers or non-smokers. Physical activity was evaluated by asking how often and for how long the participants engaged in both light and intense leisure-time physical activity. Light activity was defined as activity that did not lead to being sweaty or out of breath, while intense activity was activity that did result in sweating or breathlessness. Individuals were then divided into groups performing no physical activity, moderate physical activity and heavy physical activity. Amount of alcohol consumption was assessed using two questions: Do you abstain from alcohol? and What is your normal consumption of alcoholic beverages within 14 days?. Based on this, using a cut-off value of 15 units, participants were grouped to have no consumption, moderate consumption, or high consumption. After the first questionnaire and the clinical examination, a second questionnaire was distributed to a random subsample and completed by 8,896 individuals [53]. This questionnaire contained questions on sleep which was included as a covariate in this subsample-. Sleep was evaluated by the question How often do you experience sleep difficulties, with tick-off possibilities Never/a few times a year, Once or twice a month, Once a week and More than once a week. Participants answering one of the two first were considered as having good sleep, participants answering one of the two latter, were considered as having bad sleep. 7

8 Statistical procedure To enable a comparison between the whiplash-group and the no whiplash-group in relation to somatic symptom profiles, the reported frequency of each symptom was standardized with a mean of 0 and a standard deviation of 1. Independent t-tests were then employed to each of the standardized symptoms and the standardized mean frequency of the reported symptoms (somatization). In order to adjust for covariates, a multiple linear regression model was employed. Each covariate was adjusted for separately, but all regressions included gender. A fully adjusted model was computed, and a separate regression analysis was conducted, adjusting each symptom for all covariates. To investigate the unadjusted association between the standardized mean frequency of reported symptoms and time since accident, a linear regression model was employed. STATA/SE 10 [54] for Mac was used for all analyses. Ethics All the participants in this study gave their written consent upon inclusion. The HUSK study was approved by the Regional Committee for Medical Research Ethics of Western Norway and the Norwegian Data Inspectorate. Results In the analyzed sample (N=13,986), 403 (2.9%) individuals reported chronic whiplash. The individuals in the whiplash group reported more symptoms of anxiety and depression, and were more likely to be benefit recipients than those in the comparison group. They also reported a higher number of somatic diagnoses and worse sleep (Table 1). Compared to the group of individuals reporting no whiplash, the mean reported frequency of somatic symptoms in the whiplash group was 0.60 SD higher. When adjusting for potential covariates, the mean difference in symptom reporting was attenuated to 0.41 SD in the fully adjusted model (Table 2). The variables which separately attenuated the mean difference the most were benefit recipiency, anxiety and depression. All examined symptoms were elevated in individuals with chronic whiplash compared to those with no chronic whiplash (Figure 1). The symptoms with the largest difference in 8

9 frequency were headache, dizziness, joint/muscle pain, tiredness, paresthesia in extremities and nausea, with a mean difference at levels of 0.40 SD or higher. There was a mean difference between 0.20 to 0.40 for the symptoms shortness of breath, chest pain, abdominal pain, bloating, frequent defecation, regurgitation and burning eyes. The symptoms tongue plaque, skin discoloring, discomfort in genital region and urination problems had a mean difference between 0.10 and 0.20 SD. Fully adjusted, all individual symptoms remained statistically significant apart from urination problems (p=0.224) and discomfort in genital region (p=0.159) (Table 3). The mean time since whiplash injury was 10.8 years (range 1 to 45), and the proportion reporting chronic whiplash declined strongly with increasing time since the whiplash injury (Figure 2). The association between chronic whiplash and somatic symptoms was stronger amongst those reporting an experienced whiplash injury that occurred a long time ago, than amongst those reporting a more resent injury. The tendency was rather weak and borderline significant (within whiplash group, correlation r=0.016 (p=0.032) between time since whiplash and somatic symptoms (Figure 2)). Discussion Main findings Individuals reporting chronic whiplash also reported a higher frequency of every somatic symptom examined, and adjusting for potential confounding variables only partly accounted for this difference. These symptoms were spread across organ systems and bodily areas, whereof most are not plausibly related to a whiplash injury according to the organic whiplash hypothesis. In addition, there was a declining number of self-reported whiplash injuries with increasing time since accident, and older whiplash injuries were associated with more somatic symptoms. Strengths and limitations The main strength of this study is the population-based design enabling a comparison between a group of chronic whiplash sufferers and a healthy population. Using clinical data would complicate a study like this, due to selection bias - individuals with a heavy symptom load would to a greater extent seek medical help after a whiplash injury than others - resulting in an exaggerated symptom reporting in the chronic whiplash group. Using a population-based 9

10 design, we were able to compare all individuals reporting a whiplash injury and neck pain, including those not in contact with health services. All variables were self-reported, including exposure and outcome. Using self-reported whiplash with no medical confirmation, accepting individual differences in what is perceived a whiplash trauma, lets us study an interesting group; a mixture of individuals diagnosed by a doctor and individuals self-diagnosed. A recent study with similar research design found selfreported whiplash to strongly predict a subsequent allowance of disability benefits [40], indicating clinical relevance of self-reported whiplash. Another important advantage is the fact that both participants in the health study and the staff collecting the data were blinded to the specific hypothesis of this study. The questions related to somatic symptoms were not linked to whiplash in the questionnaire, which should minimize the risk of attribution and symptom accentuating. The study was not related to any litigation, compensation or insurance process, known to increase symptom reporting and delay recovery [55, 56]. The large number of participants and the relatively high participation rate should also be noted as advantages, as can the many covariates included in the dataset, making adjustments for multiple confounders possible. The study also has some notable limitations. The study is cross-sectional, making it difficult to conclude on causal inference - symptoms and somatization tendency might have been present before the accident. Interpretation of findings Our findings on increased symptom reporting among chronic whiplash sufferers and the positive linear association between time since whiplash injury and frequency of somatic symptoms are hard to explain within the organic model. The findings are more compatible with, and indicative evidence of, a functional element within chronic whiplash. In line with previous studies [4, 9, 10, 13, 19, 57-60], the most frequent symptoms amongst chronic whiplash sufferers were headache, neck pain/joint-muscle pain and dizziness. Other somatic symptoms have not been as thoroughly explored. Some studies have found increased levels of gastrointestinal symptoms, palpitations, shortness of breath and sleep disturbances [8, 23], but increased frequency of a wide range of somatic symptoms amongst sufferers of chronic whiplash is new. This symptom profile resembles the diffuse and 10

11 non-specific symptom profile seen amongst individuals suffering from functional somatic syndromes [24, 26, 29, 30]. Benefit recipiency, anxiety and depression were the covariates separately attenuating the association between chronic whiplash and somatic symptoms the most. Symptoms of anxiety and depression are frequently reported symptoms after whiplash traumas [7, 8, 23, 37] and among individuals reporting a wide range of somatic symptoms [24, 61-63]. Therefore, symptoms of common mental disorders may not only be confounders but also mediators, and including these symptoms might be over-adjusting the model. The finding of elevated work disability (benefit recipiency) supports the functional hypothesis. Increased reporting of symptoms of anxiety and depression are also important when aiming to determine if chronic whiplash is a functional or an organic disorder. Individuals suffering from functional somatic syndromes or somatization report increased levels of symptoms of common mental disorders [24, 61, 62], and according to the ICD-10 criteria, somatization disorder often coexists with anxiety and depression [31]. Given this, the increased reporting of symptoms of common mental disorders adds to the similarities between chronic whiplash and functional somatic syndromes. New research on whiplash and anxiety and depression enlightens this further. Earlier, the anxiety and depression seen in the chronic whiplash were interpreted as a psychological response developing after the physical damage [64]. Recent findings suggest a reverse causality with increased risk of reporting incident whiplash in follow-up if anxiety and depression were reported at baseline [40]. Also there is an increased risk of developing chronic symptoms after a whiplash injury, if depression is reported before or at time of accident [65]. This, and the fact that individuals reporting whiplash have increased risk of being awarded disability pension, also when they report no neck-pain [40], is indicative to chronic whiplash being to some degree a functional disorder. In addition to research on the symptom profile found in chronic whiplash sufferers, other aspects of the condition have been explored. Studies have shown that the outcome after a whiplash trauma is more affected by cultural expectations [2, 66] and cultural factors that generate symptom amplification and attribution [44], than by the actual speed, forces or tissue damage [2, 12, 18]. On top of the influence caused by culture, an important role on the course of the disorder is played by thoughts and emotions in relation to the accident. For instance, the feeling of not being responsible for the accident, and being angry or worried, predicts a worse outcome [56]. A dose response relationship between recovery expectations and disability has 11

12 been found, where individuals not expecting a full recovery, are more likely to have high degree of disability six months later [67]. People experiencing whiplash in relation to sports, stand out from other whiplash victims with their absence of chronic symptoms and disability [25]. These findings stand in contrast to our understanding of organic disorders, but in line with that of functional somatic syndromes [24]. Also the tendency of whiplash to develop into a chronic disorder, and the drastically varying prevalence of chronic whiplash seen in different cultures [44], is better explained by understanding whiplash as a functional somatic syndrome than an organic disorder. Finally, whiplash can be linked to functional somatic syndromes through our findings of elevated symptom reporting when the number of participants reporting whiplash decreases while time since accident increases. The tendency could be an effect of a selection process; those not having symptoms anymore, might not think of the trauma as being relevant, or might not remember it at all. Those experiencing many symptoms they regard related to the accident will however still report whiplash. These participants might be individuals suffering from psychological distress, functional somatic syndrome or increased somatization tendency, and the relation we see might be due to a greater tendency to label symptoms as whiplash [24, 40]. This importance of attribution of pre-existing symptoms to the trauma has been emphasized in previous studies [68], and is supported by the tendency to underestimate experienced symptoms such as back pain, neck pain and psychological distress experienced before the accident [69]. Clinical implications This study adds to the growing body of literature suggesting whiplash being a functional disorder [23-25]. Standard treatment of acute whiplash has been providing the patient with information on injury mechanisms (according to the organic model), advice on suitable activities, recommendations to rest the neck the first weeks, instructions on postural correction, and information on comfort and prevention from excessive movement of the neck that soft collars can provide [70]. Now, studies have concluded that active treatment is more effective [4, 70, 71] - the patient should be encouraged to do neck exercises [70] and continue an active life [25, 72]. We advocate that the traditional approach should be replaced with an approach which regards chronic whiplash a functional somatic syndrome: Similar to patients with other functional somatic syndromes, individuals having experienced a whiplash injury should be discouraged from assuming the sick-role [24, 25], and the physician should 12

13 undercut alarming expectations about clinical course [24]. For these patients, fear of pain and (re)injury may be more disabling than pain itself [73]. Also, pain-related fear and avoidance appear important factors in the development of chronic problems [73]. Conclusion In conclusion, the increased self-reported level of 17 symptoms related to somatization, the fact that neck pain and headache constituted only a small amount of the complaints among sufferers of chronic whiplash and the relationship of elevated levels of symptom reporting alongside increasing time since whiplash injury can all be seen as indicative evidence of chronic whiplash as a functional somatic syndrome. 13

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18 Table 1: Summary of the variables included in the analysis, and differences between individuals reporting chronic whiplash and individuals not reporting chronic whiplash. Covariates Chronic whiplash N=403 No chronic whiplash N=13,583 P-value (Chisquare test) All N=13,986 Female 58.3% 53.9% % Anxiety 24.1% 17.6% % Depression 14.6% 9.6% % Sleep quality <0.001 Good 37.0% 42.6% 42.4% Bad 17.9% 11.1% 11.4% Not asked 45.2% 46.3% 46.3% Education Compulsory only 13.7% 17.5% 17.4% High School 46.9% 45.7% 45.7% University 39.5% 36.8% 36.9% Benefit recipiency 28.3% 13.0% < % Sickness benefit 10.9% 4.6% 4.7% Occupational habilitation 3.5% 1.1% 1.1% Disability pension 11.9% 3.3% 3.6% Social benefit 1.5% 0.5% 0.6% Unemployment benefit 2.5% 1.6% 1.7% Dependents pension 0.5% 0.7% 0.7% Other 2.7% 2.6% 2.6% Physical activity None 17.4% 15.5% 15.6% Easy 38.7% 41.9% 41.8% Heavy 43.9% 42.5% 42.6% 18

19 Alcohol consumption No consumption 27.1% 28.3% 28.3% Moderate consumption 67.5% 66.1% 66.1% Heavy consumption 5.5% 5.6% 5.6% Daily smoking 37.5% 35.5% % Somatic diagnoses >0 11.9% 8.1% % Marital status Not married 11.2% 12.7% 12.6% Married 71.5% 74.6% 74.5% Separated 3.0% 2.4% 2.4% Divorced 13.7% 9.7% 9.8% Widow/Widower 0.7% 0.7% 0.7% Mean somatisation >2 43.2% 21.4% < % 19

20 Figure 1: Mean difference in the association between those reporting chronic whiplash and somatic symptoms compared to those not reporting chronic whiplash Mean standardised score UP SD BE DGR TP R FD AP SB B CP N PA MS H T D MEAN Somatic symptoms UP=urination problems, DGR=discomfort in genital region, SD=skin discoloring, TP=tongue plaque, BE=burning eyes, R=regurgitation, FD=frequent defecation, B=bloating, AP=abdominal pain, CP=chest pain, SB=shortness of breath, N=nausea, PA=paresthesia in extremities,

21 T=tiredness, MS=joint/muscle pain, D=dizziness, H=headache 21

22 Table 2: Mean difference of reported somatic symptoms compared between individuals reporting chronic whiplash and individuals not reporting chronic whiplash, adjustments for covariates; separately and fully adjusted. Variables B (CI) No adjustments Gender Education Benefit recipiency Anxiety a Depression a Somatic diagnosis Physical activity Consumption of alcohol Daily smoking Marital status Fully adjusted a Anxiety and depression entered as a continuous variable. 22

23 Table 3: Mean difference of reported frequency of 17 somatic symptoms compared between individuals reporting chronic whiplash and individuals not reporting chronic whiplash, unadjusted, adjusted for gender and fully adjusted. Symptoms Unadjusted B (CI) Adjusted for gender B (CI) Fully adjusted* B (CI) Abdominal pain (AP) 0.34 ( ) Nausea (N) 0.41 ( ) Bloating (B) 0.29 ( ) Tongue plaque (TP) 0.19 ( ) Regurgitation (R) 0.24 ( ) Frequent defecation (FD) 0.25 ( ) Discomfort in genital region (DGR) 0.14 ( ) Skin discoloring (SD) 0.17 ( ) Joint/muscle pain (MS) 0.45 ( ) Dizziness (D) 0.49 ( ) Tiredness (T) 0.43 ( ) Paresthesia in extremities (PE) 0.41 ( ) Burning eyes (BE) 0.20 ( ) 0.33 ( ) 0.39 ( ) 0.27 ( ) 0.18 ( ) 0.24 ( ) 0.26 ( ) 0.13 ( ) 0.17 ( ) 0.44 ( ) 0.47 ( ) 0.41 ( ) 0.40 ( ) 0.19 ( ) 0.24 ( ) 0.30 ( ) 0.19 ( ) 0.10 ( ) 0.17 ( ) 0.18 ( ) 0.07 ( ) 0.11 ( ) 0.32 ( ) 0.36 ( ) 0.25 ( ) 0.30 ( ) 0.12 ( ) 23

24 Headache (H) 0.50 ( ) Shortness of breath (SB) 0.36 ( ) Chest pain (CP) 0.35 ( ) Urination problems (UP) 0.12 ( ) 0.48 ( ) 0.36 ( ) 0.35 ( ) 0.11 ( ) 0.40 ( ) 0.25 ( ) 0.26 ( ) 0.06 ( ) *Adjusted for gender, anxiety, depression, education, benefit recipiency, physical activity, marital status, consumption of alcohol, daily smoking and somatic diagnosis 24

25 Figure 2: Somatic symptoms, frequency of participants reporting whiplash and time since accident Degree of somatic symptoms Frequency Years since whiplash injury Point estimate 95% CI Regression line