|
THE LATE WHIPLASH
SYNDROME: A PSYCHOPHYSICAL STUDY
Martina Moogc, John
Quintnerb, Toby Halla and Max
Zusmana
a School
of Physiotherapy, Curtin University of Technology, Shenton Park WA
6008 (Australia), bWyllie Arthritis Centre, Shenton Park
WA 6008 (Australia)
cCorresponding Author:
Martina Moog, University of Sydney, Pain
Management and Research Centre, Royal North Shore Hospital, St.
Leonards NSW 2065, Australia, Tel: +61-2-9926 7990, Facsimile:
+61-2-9926 6548, Email: mmoog@doh.health.nsw.gov.au
Category: Clinical
article
Keywords: Whiplash
injury, Allodynia, Secondary Hyperalgesia, Psychophysics,
SCL-90-R
ABSTRACT
Some patients
who have sustained whiplash injuries present with chronic widespread
pain and mechanical allodynia. This single blind, case control matched
study of 43 chronic whiplash patients sought to examine
psychophysical responses to non-noxious stimuli and their
relationship to psychological profiles.
Symptom Check List-90-R, Neck
Disability Index and Shortform McGill Questionnaire were completed
prior to testing. Qualitative stimuli comprised light-touch,
punctate pressure, moderate heat and cold. Additionally, sustained
vibration was administered using a vibrameter which allowed ramping
of either frequency or amplitude.
Twenty-eight
patients reported vibration-induced pain. No control subject
experienced pain in response to vibration. No significant
differences in perception threshold to vibration were noted between
patients and control group. Twenty-three patients and ten control
subjects reported painful responses to cold. Eleven patients and
nine control subjects experienced pain in response to moderate heat.
Four patients rated punctate pressure and one patient rated
light-touch as painful.
SCL-90-R
profiles revealed an overall elevated level of distress in the
whiplash group. No significant difference was found between patients
with and without vibration-induced pain for any dimension of the
SCL-90-R.
Pain
in response to non-noxious stimulation over presumably healthy
tissues suggests that central mechanisms are responsible for ongoing
pain in at least some whiplash patients. The additional findings of
pain on punctate pressure and hyperalgesic responses to heat and
cold stimuli are consistent with enhanced central responsiveness to
nociceptor input. These results have important therapeutic and
prognostic implications.
INTRODUCTION
In
Western societies motor vehicle insurance claims due to
‘whiplash-type’ injuries have been described as reaching ‘epidemic’
proportions (Spitzer et
al., 1995; Ratcliff, 1997). Those who become chronically
disabled impose a major social and financial burden upon society
(Barnsley et al., 1994;
Gargan et al., 1997,
Ferrari and Russel, 1999a).
The
pathogenesis of the so-called ‘late whiplash syndrome’ (Pearce,
1989) is poorly understood (Koelbaek Johansen et al., 1999). Some maintain
that chronic pain and disability reflect the influence of such
‘environmental’ factors as management interventions by health care
professionals and the medico-legal process (Schmand et al., 1998; Ferrari and
Russell, 1999b; Obelieniene et al., 1999; Pearce 1999;
Cassidy et al., 2000).
Others argue that ongoing
pain is likely to have a somatic basis and that any associated
physical and psychological disability are secondary, in so far as
they resolve coincidentally with pain relief (Radanov et al., 1995, Radanov et al. 1999; Wallis et al., 1998). Cervical
zygapophyseal joints have been proposed as a possible anatomical
source of chronic pain in at least 50% of these patients (Wallis et al.,
1997).
Animal
experimental studies have shown that tissue injury causing prolonged
noxious input can produce functional changes within the central
nervous system which are maintained long after nociceptive input has
disappeared or has become minimal (Woolf and Doubell, 1994). This
state, which is known as central sensitization, is manifested as an
increased response or reduced threshold to afferent input, prolonged
after-discharges to repeated stimulation, an expansion of the
receptive fields of dorsal horn neurones and an increase in their
spontaneous activity (Coderre et al., 1993; Devor, 1994;
Koltzenburg et al.,
1994).
The clinical correlates of central
sensitization are likely to be hyperalgesia (an increased response
to a noxious stimulus) (Merskey and Bogduk 1994), allodynia (pain in
response to a non-noxious stimulus) (Merskey and Bogduk 1994),
widespread pain, and stimulus-independent pain (Coderre et al., 1993). There is an
emerging body of evidence derived from psychophysical testing which
is consistent with an underlying state of hypersensitivity in the
central nervous system of patients presenting with chronic neck pain
(including some with pain following whiplash injury) (Hagström and
Carlsson, 1996; Sheather-Reid and Cohen, 1998; Koelbak Johansen et al., 1999).
The aim of this
study was to determine whether such a condition is present in a
larger group of patients fulfilling the criteria for ‘late whiplash
syndrome’. As one of the authors had previously observed that
sustained vibration at 100 Hz (delivered by a commercially available
appliance) was perceived as a painful stimulus by some sufferers of
chronic neck pain, it was decided to use this modality of sensory
testing, in addition to standard tests of cutaneous sensory
function.
MATERIALS AND
METHODS
Subjects
The inclusion
criteria were based on the classification adopted by the Quebec Task
Force (Spitzer et al 1995). Patients in Classes I and II with
symptoms of more than six months duration subsequent to a
motor-vehicle accident (MVA) were selected for the study. Patients
with discernible musculoskeletal disorders, objective neurological
deficits, or obvious psychopathology were not included in the study.
The patient sample was not biased to either age or sex. A control
group consisted of age and sex-matched healthy volunteers with no
complaints of spinal, upper or lower limb pain or of injuries to the
head, shoulder or knee regions necessitating medical treatment or
time off work in the 12 months prior to
testing.
All participants
in the study were unpaid volunteers, living within the Perth
metropolitan area and unconnected with this study. They had been
referred from pain clinics and selected private practices in
rheumatology and physiotherapy. All had given their informed written
consent to a protocol approved by the Ethics Committee of Curtin
University. Patients were allowed to continue taking their usual
medication. It was not considered ethical or practicable to insist
on a “wash-out” period of 24 hours before sensory testing, as many
patients complained of pain that interfered with their ability to
carry out normal daily activities.
Data Collection
Prior to
psychophysical testing, demographic and health-related
questionnaires were administered to all participants. In addition,
specific accident-related information and symptomatology as
recollected from acute phase were collected from the whiplash group.
The Symptom Check List-90-R (SCL-90-R) (Derogatis, 1994) was used to
assess psychological status of all participants. The Neck Disability
Index (NDI) (Vernon, 1996) was used to provide an assessment of the
extent of perceived functional disability in the whiplash
patients.
All sensory
tests were performed by a single individual. Blinding of the
investigator had been considered during the design of the study.
However, it was decided to simulate, as far as possible, the normal
clinical situation. Instructions given to each participant
were standardized and care was taken not to provide information
about expected test outcomes or about the research
hypothesis.
Experiment 1: Qualitative psychophysical
testing
In each participant, four standard
cutaneous stimuli were used (Asbury, 1998). The aim was to stimulate
different types of peripheral receptors using light-touch, punctate
pressure, non-noxious cold and heat and to obtain a descriptive
interpretation of stimulus quality by the participants. The stimuli
were applied in a random order to the skin over the belly of the
upper trapezius muscle on either side and over the central sternum.
Each participant was asked to identify the presence and the quality
of the stimulus for each area. Any differences in reported sensation
between the areas were noted. For the thermal stimuli the
participants were also instructed to rate the intensity of any
painful sensation on a numerical rating scale from 0 to 100.
To elicit a
sensation of light-touch, a cotton ball was fixed to a clamp and
gently stroked four times across each test site. Touch pressure was
applied over each site through a hand held Semmes-Weinstein
monofilament (size 6.45). Two metal probes were used to assess
thermal sensibility (Hot/Cold Discrimination kit with calibrated
thermometers, Smith & Nephew Roylan Inc.). The cold probe was
placed in ice and water (0°C) and the heat
probe in warm water (40-41°C). The
respective probes were maintained at a constant temperature. During
application of heat and cold stimuli, the skin was touched obliquely
with the rounded end of the metal probe for five seconds. The
pressure applied was insufficient to indent the underlying
skin.
Experiment 2: Quantitative psychophysical
testing
Measurements were performed using a
purpose built vibrameter with adjustable frequency (0-100Hz) and
amplitude (0-2.5mm - peak to peak). The vibrating element
produces pure sine waves that are transmitted by a small element,
emerging from a supporting base. The possible influence of different
application pressures on the accuracy of the readings is thereby
minimised when the instrument is gently placed over soft tissues. A
LED display indicates the frequency and amplitude of the delivered
vibratory stimuli. The device was calibrated prior to testing and it
was found to be accurate between 0.02-0.04mm for amplitude and between 1-2Hz for
frequency. The resolution of the instrument was specified as being
below 0.04mm for amplitude and ± 1Hz for frequency.
The vibration device was clamped to the end of
an articulated arm, which was fixed to a portable trolley, thus
ensuring stable application of the stimulus. Vibration was applied
to skin over three test sites on each side of the body: the belly of
the upper trapezius, the belly of the deltoid muscle, and the belly
of the quadriceps muscle.
Different pre-determined test patterns were
used to ensure that the stimulation sequence over the six test sites
was conducted in a random manner. Randomization was necessary to
exclude any potential reporting bias due to testing within or
outside the area of described pain. From the available literature,
it was unclear whether greater mechanical stimulation would result
from increases in vibration frequency or in amplitude. Therefore,
stimulation at each test site commenced alternately either with
increasing frequency or amplitude in an ascending manner.
Vibration perception threshold (VPT) was
determined by the subject operating a buzzer when first becoming
aware of the stimulus. Amplitude or frequency readings were then
recorded. The stimulus was further increased, either to a frequency
of 100Hz, or to an amplitude of 1.0mm, whilst the other modality was kept constant
at 0.2mm or 20Hz respectively. The participants were
instructed to again sound the buzzer at the onset of any
vibration-induced pain (VIP), thus providing an assessment of pain
threshold. The location and the character of this pain were recorded
on a body chart. If the participant was in pain prior to
commencement of vibration testing, the buzzer was to be sounded if
the intensity of pain increased or if pain spread into a ‘new’ body
area. Unless there had been intolerance to submaximal stimulation,
maximum vibration frequency or amplitude was maintained for 30
seconds at each test site.
Statistical methods
Descriptive statistics, normality testing
(Lilliefors statistic) and Mann-Whitney-U test or 2-tail unpaired
t-test were applied to cutaneous and vibration test results, and to
the questionnaire. Pearson’s correlation coefficient or Spearman’s
rank order correlation (rho) were used to assess the relationship
between functional, psychological and pain scores. The significance
level for all parametric/non-parametric tests was set at p<0.05.
A logistic regression model evaluated the prognostic value of
post-injury symptomatology, self-reported pain intensity with
thermal stimuli and questionnaire scores in order to predict the
presence of VIP in the patient group.
Reliability testing (Wilcoxon Signed Rank test
and Spearman Rank Correlation) was conducted for the VPT/VIP in a
subset of 16 healthy control participants and in the first 11
whiplash patients who had responded with VIP and agreed to undergo
repeat testing.
RESULTS
Demographic details
Forty-three patients, comprising 15 males and
28 females, of mean age 37 years (range 12-66 years), complained of
neck and upper back pain of more than 6 months duration (median 18
months) following their involvement in a MVA. The commonest type of
MVA were rear-end collisions (56%), followed in frequency by frontal
(16%) and side-on (16%) collisions. Forty-three control subjects who
were age and gender matched with the whiplash sample participated in
the study.
At the time of their accident, 34 patients had
been employed. Of these, 25 had taken on average 12-13 days off
work, 6 had changed their occupation as a result of the accident and
8 had not returned to work. All had received ongoing medical
treatment, which consisted mainly of analgesics, non-steroidal
anti-inflammatory drugs and various modalities of physical
treatment. Twenty-eight patients were involved in ongoing
litigation, ten had settled their claims and five had never sought
compensation for personal injury.
Comparing the subjective reports, the intensity
of neck pain and the presence of concentration problems appear to
have remained constant since the accident. The incidence of headache
tended to have declined, whereas that of referred pain (into
shoulders and arms) to increase slightly with the passage of time.
Other symptoms were rated as being less frequent with the passage of
time (Table 1).
|
Table 1. –
Self-reported symptoms acute (<2 weeks) and chronic (>6
months) |
|
SYMPTOM |
ACUTE |
VAS
scores |
CHRONIC |
VAS
scores |
|
|
n |
% |
Mean |
SD |
n |
% |
Mean |
SD |
|
Neck Pain |
43 |
100% |
82 |
15 |
43 |
100% |
67 |
15 |
|
Headache |
43 |
100% |
77 |
21 |
38 |
88.4% |
74 |
19 |
|
Shoulder Pain |
38 |
88.4% |
64 |
32 |
41 |
95.3% |
61 |
18 |
|
Arm Pain |
26 |
60.5% |
39 |
37 |
25 |
58.1% |
59 |
22 |
|
Pins and Needles |
22 |
51.2% |
- |
- |
19 |
44.2% |
- |
- |
|
Numbness |
17 |
39.5% |
- |
- |
10 |
23.3% |
- |
- |
|
Dizziness |
23 |
53.5% |
- |
- |
4 |
9.5% |
- |
- |
|
Blurred vision |
15 |
34.8% |
- |
- |
6 |
14.3% |
- |
- |
|
Tinnitus |
13 |
30.9% |
- |
- |
1 |
2.4% |
- |
- |
|
Concentration |
24 |
55.8% |
- |
- |
24 |
55.8% |
- |
- |
|
|
|
|
|
|
|
|
|
|
Pain distribution
At the time of testing, patients most commonly
reported pain in the neck, shoulders, scapulae, and head. Next, in
descending order of frequency, were the dorsal upper arms, lumbar
region, interscapular region, thoraco-lumbar junction, and posterior
thigh. Leg pain only occurred in those complaining of widespread
spinal pain. Twenty-three patients reported either continuous or
intermittent paraesthesiae, described as numbness and/or ‘pins and
needles’, most frequently felt in their hands (dermatomes
C6/7/8).
Qualitative psychophysical
testing
All participants were able to perceive and
correctly identify each of the four cutaneous stimuli. One patient
reported that light touch over the pain-dominant shoulder was
painful. Four patients rated punctate pressure applied in the region
of their shoulder pain as painful. Eleven patients described a
painful response to heat and twenty-three to cold stimulation. In
the control group no participant reported pain in response to
light-touch or punctate pressure, but ten experienced cold
stimulation as painful and nine reported heat as painful. However
pain felt on thermal stimulation was self-rated on a numerical scale
as being 2-3 times higher in the whiplash patients (34/100 for heat,
29/100 for cold) than in the controls (14/100 for heat, 10/100 for
cold).
Quantitative psychophysical
testing
In all participants VPT was reported in the
first 10-15% of available frequency and in the first 9-14% of
available amplitude range. Normality testing was conducted on all
perception threshold data collected from each individual test site.
The results were positively skewed. Mann-Whitney U-tests showed no
significant difference in vibration perception threshold between
patients and control participants at the p<0.05 level. No
significant differences in VPT were found between pre-test painful
and non-painful test sites (Table 2).
|
Table 2. -
Comparisons for VPT between whiplash and
control group |
|
Groups° |
n 1
W |
n 2
C |
Test
point |
Mann-Whitney
U |
Significance
2-tailed p |
|
Frequency measurements |
|
W vs C |
43 |
43 |
Knee |
886 |
0.73 |
|
|
43 |
43 |
Trapezius |
817.5 |
0.35 |
|
|
43 |
|
Deltoid |
870 |
| |