Correlation between self-reported recovery and central sensitization in whiplash patients

Robert Ferrari

Departmentof Medicine,University of Alberta,Edmonton,Alberta T6G 2P4,Canada

Correlation between self-reported recovery and central sensitization in whiplash patients

Robert Ferrari

Departmentof Medicine,University of Alberta,Edmonton,Alberta T6G 2P4,Canada

Background:Central sensitization has been associated with chronic pain in whiplash patients.

Methods:Consecutive whiplash patients were assessed at 3 months post-whiplash injury with the brachial plexus provocation test(BPPT)as a sign of central sensitization.Self-reported recovery was assessed by the response to the question‘Do you feel you have recovered fully from your accident injuries?’

Results:Sixty-nine subjects(32 males,37 females,age 37.5±13.0 years(mean±SD),range 18—71)were included.Of these,34 reported a lack of recovery,and 35 reported recovery at 3 months post-injury.The mean BPPT elbow extension(from 180°)was 41.5±23.0°,and the mean VAS score for the BPPT was 2.2±1.2(outof10).Those who reported recovery had a mean BPPT elbow extension angle of25.1±15.8 while those who did notreportrecovery had a mean BPPT angle of 58.4±15.9(P＜0.05).The visualanalogue scale(VAS)score for recovered subjects was 1.8±1.1 and 2.7±1.1(P＜0.05)for non-recovered.There was a moderate correlation between self-reported recovery and BPPT elbow extension angle(-0.44)and a lower correlation between self-reported recovery and VAS score(-0.30).

Conclusion:Self-reported recovery correlates well with a lower likelihood of signs of central sensitization.

Copyright?2012,Shanghai University of Sport.Production and hosting by Elsevier B.V.All rights reserved.

Brachial plexus provocation test;Central sensitization;Self-reported recovery;Whiplash injury

1.Introduction

Central sensitization has become an importanttopic in the study of whiplash-associated dissorders.1—5It has been postulated that chronic pain in whiplash-associated disorders is the result of or involves the phenomenon of central sensitisation.1—3Thatis,following acute whiplash injury,and resolution of the inflammation and process of healing of theperipheral pathology,it is postulated that some individuals continue to have pain in the absence of a peripheralstimulus. This phenomenon is called central sensitisation.Prolonged or strong activity of dorsal horn neurons caused by repeated or sustained noxious stimulation may subsequently lead to increased neuronal responsiveness or central sensitisation.6,7Neuroplasticity and subsequent central nervous system sensitization include altered function of chemical,electrophysiological,and pharmacological systems.8—10These changes cause exaggerated perception of painful stimuli(hyperalgesia),a perception of innocuous stimuli as painful(allodynia)and may be involved in the generation of referred pain and hyperalgesia across multiple spinal segments.11—14Nevertheless,the extent to which it is a result or a cause of chronic pain(or both)has not been fully elucidated.1The presence of ongoing signs of central sensitization may reflect a lack ofrecovery,butmeasurementof centralsensitization inthe primary care setting is challenging,requiring either specific physical examination measures or instruments.2

Recovery from whiplash injury can be assessed by a number of measures.Increasingly,rather than relying on lengthy instruments,such as disability questionnaires,or physical examination measures,studies suggest that single questions dealing with self-reported recovery have good testretest reliability15and correlate well with other measures, such as resolution of pain-related limitations and resolution of neck pain intensity,15as well as low whiplash disability scores.16

The use of straightforward,easily-applied single question approaches is more likely to be of value to busy primary care practitionersthan more complicated measures,butitisnotclear how self-reported recovery correlates to measures on physical examination,especially measures of centralsensitization.

There are many methods reported to assess central sensitization.2Most require specialized equipment.One method reported to be usefulincludes the brachialplexus provocation test(BPPT).2This involves a physical examination maneuver where the measures are an angle at the elbow and pain levelon a visual analogue scale.It is considered an indication of sensitization or hyperexcitability via a lowered threshold to a mechanical(movement)stimulus.The test also has high reliability.2

The purpose of this study was to determine how selfreported recovery correlates to BPPT results 3 months postwhiplash injury.

2.Methods

This was a cohort study of consecutive whiplash-injured patients presenting within 7 days of their collision to a single walk-in primary care centre,and assessed at that centre 3-months post-injury.Informed consent was obtained, and ethical clearance was gained from the Health Ethics Research Board of the University of Alberta.

The timelines of the study are as follows.Prospective subjects were assessed within 7 days of their collision.They were assessed for inclusion and exclusion criteria at the time of initialinterview.Whiplash-associated disorder grade 1 or 2 patients were included if they were seated within the interior of a car,truck,sports/utility vehicle,or van in a collision(any of rear,frontal or side impact),had no loss of consciousness, and were 18 years of age or over.Patients were excluded if they were told they had a fracture or neurological injury(i.e. grade 3 or grade 4 whiplash-associated disorders),had objective neurologic signs on examination(loss of reflexes, sensory loss),previous whiplash injury or a recollection of prior spinal pain requiring treatment,no fixed address or current contact information,were unable to communicate in English,had non-traumatic pain,were injured in a non-motor vehicle event,or were admitted to hospital.A total of 89 prospective subjects were assessed,and from these 20 were excluded(18 due to previous history,two due to loss of consciousness).Thus,69 subjects formed the cohortfor study, to be evaluated at3 months post-collision by the author.Atthe outset,data was collected regarding the age,gender and Whiplash Disability Questionnaire(WDQ)4scores(when they first presented for care).

At 3 months post collision,subjects completed a questionnaire containing a single question concerning recovery. Recovery was assessed by asking“Do you feel you have recovered fully from your accident injuries?”The responses included“yes”,“no”or“notsure”.Those who responded“no”and“not sure”were deemed not recovered.This question has been shown to correlate well with WDQ scores.4No data was gathered on treatment during the last three months.

Also at 3 months post-injury,the BPPT was performed while the examiner was blind to the results of the other data. The BPPT was performed as described elsewhere.2In brief, the BPPT was always performed on the left side first,the technique involving the application of gentle shoulder girdle depression,glenohumeral abduction and external rotation in the coronal plane,with wrist and finger extension and elbow extension.The range of elbow extension was measured at the subjects’pain threshold using a standard goniometer aligned along the mid-humeral shaft,medial epicondyle and ulnar styloid.If the subject did not experience pain,the test was continued until the end of available range.At the completion of this test,the subjects were asked to record their pain on a 10-cm visual analogue scale(VAS).

All subjects were,at the time of the study,in a system of new legislation thatplaces a cap on compensation forwhiplash grade 1 and 2,of$4000 CAN,with a standardized diagnostic treatment protocol applied to each subject.This system has been described elsewhere.17Allsubjects had filed a claim with an insurance company to receive treatment benefits.

Crude associations between age,gender,initial WDQ,and BPPT angle and VAS score were assessed usingχ2tests,with αlevelssetat0.05.Forage,the clinically meaningfulcategories were age≤40 and age＞40.As the distribution of age and WDQ scores may not be normal,these continuous variables were also converted to categoricalvariables.For age,the clinically meaningfulcategories(shown to have prognostic significance)were age≤40 and age＞40.For WDQ,the clinically meaningfulcategories were scores in the low(0—40),medium (41—80)and high(81—130)range.After examining for confounding and interactions,the remaining termswere included in a final logistic regression.Spearman’s rank correlation coefficientwascalculated forrecovery and both BPPTangle and VAS score.Significance was set at p＜0.05.All analyses were completed using STATA/SE,version 10.0 for Macintosh (STATA CORP,College Station,TX,USA).

3.Results

The 69 subjects were 32 males,37 females,mean age 37.5±13.0 years(range 18—71,mean±SD).Atthe 3-month follow-up,recovery was reported by 35 of 69 subjects.

Age,gender,and initial WDQ score did not correlate recovery orBPPT results,and therefore the group was analysed as a whole.At the 3-month follow-up,the BPPT elbowextension(from 180°)was 41.5±23.0°(mean±SD),and the VAS score for the BPPTwas2.2±1.2(outof10,mean±SD).

As there were no side-to-side differences,the results of both sides were averaged.Table 1 shows the mean BPPTangle and VAS score for the recovered and non-recovered groups. Those who reported recovery had a mean BPPT elbow extension angle of 25.1±15.8 while those who did notreport recovery had a mean BPPT elbow extension angle of 58.4±15.9.The VAS score was 1.8±1.1 for recovered subjects and 2.7±1.1 for non-recovered.There was a moderate correlation(Spearman’s rank correlation coefficient)between self-reported recovery and BPPT elbow extension angle(-0.44)and a lower correlation between selfreported recovery and VAS score(-0.30).

4.Discussion

This study shows thatself-reported recovery correlates well with the physical examination findings of the BPPT.Both could be used interchangeably to assess recovery,or the inclusion of the BPPT may give the practitioner additional information on which to make treatmentdecisions.

Clearly the use of a self-report recovery question alone is simpler for the busy clinician.The problem with the BPPT is that there is as yet no normative database in the healthy population for this test.At best,we have limited samples of control groups with which to compare.2All one may find is that groups differ in terms of the BPPT results,i.e.,recovered subjects have different results than non-recovered subjects. The BPPT results from this study agree in some aspects with other cohorts.2The recovered group of this study and that reported by Sterling et al.2have similar BPPT results.The non-recovered subjects of the current study have significantly more abnormal BPPT results than reported for non-recovered subjects studied by Sterling etal.2butsmallsample sizes,and the differenttime points of assessment(3 months in this study vs.6 months with Sterling et al.2)do not allow for reliable, direct comparisons of these data.

If central sensitization is an important mechanism in chronic pain after whiplash injury,it is important to understand its correlation to self-reported recovery.Given the constraints of primary practice,practitioners can most easily assess recovery by asking a single question:“Do you feelyou have recovered fully from your accident injuries?”with responses of“yes”,“no”,or“notsure”.Those who reportself-selfrecoverywill have essentially a “more normal” BPPT test, andmight not be labelled as having central sensitization by thistest. On the other hand, those who do not report recovery willhave significantly higher BPPT angles and VAS scores.Perhaps, if central sensitization persists in those reporting nonrecovery,then treatment directed at central sensitization maybe important to assist recovery; although, the best way to treatcentral sensitization is unknown, and even whether we shouldtreat it is unclear.

Table 1Brachial plexus provocation test elbow extension(BPPT)angle and visual analogue score(VAS)according to presence or lack of self-reported recovery. (A greater,more negative in direction from 180°,angle and greater VAS is more abnormal for this test.)

This study is limited by the fact that there were no otherphysical examination findings, such as spine range of motiontaken into consideration. Yet, spine range of motion at a singleassessment may not be relevant if previous range is unknown. Inaddition, the pre-test symptom of arm pain was not recorded;however, studies have not found there to be a difference inBPPT results between whiplash patients with or without armpain.2,3In addition, these findings of a correlation between selfreportedrecovery and the BPPT may not hold for othermeasures of central sensitization, such as cold threshold, heatthreshold, pressure sensitivity, etc. Future studies should assesseither the correlation between self-reported recovery andcentral sensitization test measures, or the specificity andsensitivity of each of these measures for self-reported recovery.Finally, while there is a correlation between the BPPT results (aresult of central sensitisation) and self-reported recovery, thisdoes not indicate a causal mechanism, since chronic pain, orrecovery, is complex and may be determined by a multitude offactors not assessed in this study. Further study betweenmeasures of recovery and central sensitisation as well asstability of these measures over time will be required.

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Received 27 October 2011;revised 11 December 2011;accepted 3 January 2012

E-mail address:rferrari@shaw.ca

Peer review under responsibility of Shanghai University of Sport

Production and hosting by Elsevier

2095-2546/$-see front matter Copyright?2012,Shanghai University of Sport.Production and hosting by Elsevier B.V.All rights reserved.

10.1016/j.jshs.2012.01.002