The Clinical Course of Whiplash Associated Disorders
The Clinical Course of Whiplash Associated Disorders
This is one of the first studies intending to externally validate findings from previous explorative studies on prognostic factors in acute WAD in an initially self-selected MILD sample. The MILD sample reported consistently less imposition in all clinical variables compared to the MOD/SEV sample. The MILD sample decreased statistically in pain-related disability, pain catastrophising, and post traumatic stress symptoms over the first year after the accident, whereas functional self-efficacy and fear of movement/(re)injury increased. Pain intensity was low and stable. The reported changes were small on a group level and the clinical importance can be questioned. We found that 5% of the sample reported a clinically relevant deterioration in pain-related disability. Although very few they may represent those patients declining treatment in the acute phase, but reported to show up in health care later on.
Pain-related disability at baseline emerged as the only indicator of prognosis after 12 months. Hence the prediction model was not valid in the MILD sample except for the contribution of pain-related disability. Based on a systematic review and meta-analysis, Walton et al. established a cut-off point of 5.5 of 10 on a visual analogue pain scale, with pain greater than this approaching a sixfold increase in the risk of persistent pain or disability over time. In our sample only 8 participants (11%) reported pain intensity ≥ 5 on the NRS at baseline, which could be one possible explanation of why pain did not emerge as a predictor in this sample.
An ongoing discussion is whether psychological variables measured in close connection to the accident are crucial for the prognosis, irrespective of levels of pain intensity and disability. It is proposed that the most important changes come off during the course of the first three months, and it is well established that psycho-social factors play an important role for the transition from subacute to chronic pain in other pain populations. Our study points to that those classified with WAD grade I or II and subjectively mildly affected, already in the acute phase reported lower levels in psychological variables compared to those reported being moderately to highly affected and in need of treatment. The mechanisms behind the co-existence of low pain intensity, low pain-related disability and low imposition of psychological variables is of great interest but there was no possibility to rule out the temporal relationship between these variables in the acute stage in either of the samples. It has been proposed that psychological variables mediate the relationship between pain intensity and disability in WAD and this mediation may be stronger when pain and disability are more severe. Theoretically, behavioral learning principles may explain how experiences from previous accidents and pain conditions shape the current experience of the WAD and the development over time. For instance, recovery beliefs in the acute phase are associated with prognosis, and may be a result of such a previous learning process. Holm and colleagues found that persons who stated they were less likely to make a full recovery were more likely to have high disability 6 months after the accident compared to persons who stated that they were likely to make a full recovery. We did not include any measure of recovery beliefs in the present study, but consider the possibility of positive recovery beliefs being a latent variable for the perception of being in no need of further treatments. The addition of this variable could have provided valuable information to our findings. The temporal dimensions and complex interaction between pain intensity, psychological variables and disability in the acute stage should be further elucidated in future studies. Another option for future research is to study the moderating effect of background characteristics on outcome. A somewhat surprising result was that the MILD reported proportionately lower levels of physical activity before the accident. A suggestion for future research is to study whether personal activity goals are related to perceived needs of treatment and pain-related disability. A previous study identified several activity related stressors in individuals with acute WAD and knowledge is needed on how personal activity demands affect outcome and adaptation to the condition.
There are some important limitations with this study which are necessary to consider when interpreting the results. The sample was partly self-selected based on subjective statements of being mildly affected and in no need of treatment, which threatens the external validity of the results to those mildly affected without being under considerations for treatments within a randomized trial. Nevertheless, the systematically collected clinical data at baseline confirmed participants' statements of being mildly affected, at least on a group level. Our prediction model was based on one point in time measures, whereas Sterling and colleagues accentuate the value of inclusion of time-changing variables for the study of prognostic factors. We considered the inclusion of change scores in our predictive model, but did not find it motivated since changes over time were small. Instead we stayed with our initial research question of validation of previously identified predictors of prognosis in this particular subsample. The risk of floor effects in the pain intensity and pain-related disability measure should also be considered. Particularly in connection to clinically relevant improvements, which has been reported to 11 points or more on the PDI. Thirty-one participants reported a score of 0 on the PDI at the 12-month follow-up. At first glance these were considered as recovered, but there is a possibility that the PDI may not be sensitive enough to capture variations in mild residual disability. Whether such variation is of clinical importance is though hard to rule out. The reliability of the pain intensity measure can also be questioned. Recalling average pain over a two-week window may introduce recall bias. For future studies it would be more feasible to use a composite score of daily ratings on pain intensity. The study of how the MOD/SEV sample developed over time and the validation of the prediction model in this sample would have been of great interest. However, only a small subsample (n = 19) was left with minimal treatments (standard self-management instructions), which did not allow for any multivariate linear regression analysis. Complete data from the RCT will be reported in the near future. Finally, it is worth noting that this study does not render any data on the causal influence on pain-related disability. Controlling for confounders is therefore not relevant at this stage.
Discussion
This is one of the first studies intending to externally validate findings from previous explorative studies on prognostic factors in acute WAD in an initially self-selected MILD sample. The MILD sample reported consistently less imposition in all clinical variables compared to the MOD/SEV sample. The MILD sample decreased statistically in pain-related disability, pain catastrophising, and post traumatic stress symptoms over the first year after the accident, whereas functional self-efficacy and fear of movement/(re)injury increased. Pain intensity was low and stable. The reported changes were small on a group level and the clinical importance can be questioned. We found that 5% of the sample reported a clinically relevant deterioration in pain-related disability. Although very few they may represent those patients declining treatment in the acute phase, but reported to show up in health care later on.
Pain-related disability at baseline emerged as the only indicator of prognosis after 12 months. Hence the prediction model was not valid in the MILD sample except for the contribution of pain-related disability. Based on a systematic review and meta-analysis, Walton et al. established a cut-off point of 5.5 of 10 on a visual analogue pain scale, with pain greater than this approaching a sixfold increase in the risk of persistent pain or disability over time. In our sample only 8 participants (11%) reported pain intensity ≥ 5 on the NRS at baseline, which could be one possible explanation of why pain did not emerge as a predictor in this sample.
An ongoing discussion is whether psychological variables measured in close connection to the accident are crucial for the prognosis, irrespective of levels of pain intensity and disability. It is proposed that the most important changes come off during the course of the first three months, and it is well established that psycho-social factors play an important role for the transition from subacute to chronic pain in other pain populations. Our study points to that those classified with WAD grade I or II and subjectively mildly affected, already in the acute phase reported lower levels in psychological variables compared to those reported being moderately to highly affected and in need of treatment. The mechanisms behind the co-existence of low pain intensity, low pain-related disability and low imposition of psychological variables is of great interest but there was no possibility to rule out the temporal relationship between these variables in the acute stage in either of the samples. It has been proposed that psychological variables mediate the relationship between pain intensity and disability in WAD and this mediation may be stronger when pain and disability are more severe. Theoretically, behavioral learning principles may explain how experiences from previous accidents and pain conditions shape the current experience of the WAD and the development over time. For instance, recovery beliefs in the acute phase are associated with prognosis, and may be a result of such a previous learning process. Holm and colleagues found that persons who stated they were less likely to make a full recovery were more likely to have high disability 6 months after the accident compared to persons who stated that they were likely to make a full recovery. We did not include any measure of recovery beliefs in the present study, but consider the possibility of positive recovery beliefs being a latent variable for the perception of being in no need of further treatments. The addition of this variable could have provided valuable information to our findings. The temporal dimensions and complex interaction between pain intensity, psychological variables and disability in the acute stage should be further elucidated in future studies. Another option for future research is to study the moderating effect of background characteristics on outcome. A somewhat surprising result was that the MILD reported proportionately lower levels of physical activity before the accident. A suggestion for future research is to study whether personal activity goals are related to perceived needs of treatment and pain-related disability. A previous study identified several activity related stressors in individuals with acute WAD and knowledge is needed on how personal activity demands affect outcome and adaptation to the condition.
There are some important limitations with this study which are necessary to consider when interpreting the results. The sample was partly self-selected based on subjective statements of being mildly affected and in no need of treatment, which threatens the external validity of the results to those mildly affected without being under considerations for treatments within a randomized trial. Nevertheless, the systematically collected clinical data at baseline confirmed participants' statements of being mildly affected, at least on a group level. Our prediction model was based on one point in time measures, whereas Sterling and colleagues accentuate the value of inclusion of time-changing variables for the study of prognostic factors. We considered the inclusion of change scores in our predictive model, but did not find it motivated since changes over time were small. Instead we stayed with our initial research question of validation of previously identified predictors of prognosis in this particular subsample. The risk of floor effects in the pain intensity and pain-related disability measure should also be considered. Particularly in connection to clinically relevant improvements, which has been reported to 11 points or more on the PDI. Thirty-one participants reported a score of 0 on the PDI at the 12-month follow-up. At first glance these were considered as recovered, but there is a possibility that the PDI may not be sensitive enough to capture variations in mild residual disability. Whether such variation is of clinical importance is though hard to rule out. The reliability of the pain intensity measure can also be questioned. Recalling average pain over a two-week window may introduce recall bias. For future studies it would be more feasible to use a composite score of daily ratings on pain intensity. The study of how the MOD/SEV sample developed over time and the validation of the prediction model in this sample would have been of great interest. However, only a small subsample (n = 19) was left with minimal treatments (standard self-management instructions), which did not allow for any multivariate linear regression analysis. Complete data from the RCT will be reported in the near future. Finally, it is worth noting that this study does not render any data on the causal influence on pain-related disability. Controlling for confounders is therefore not relevant at this stage.
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