Moog M, Quinter J, Hall T, Zusman M. The late whiplash syndrome: a psychophysical study. Euro J Pain 2002;6:283–294

Moog et al. (2002) studied a group of chronically distressed whiplash patients, known to score high on somatization scales on the SCL-90-R, and compared them to a control group consisting of age- and sex-matched healthy volunteers with no spinal, upper or lower limb pain in the 12 months prior to testing. They found that not only are the whiplash patients chronically distressed, they also have this convenient phenomenon known as “central sensitization”. We say that this is a convenient phenomenon because it cannot be proven or disproved. There is no “gold standard” for the identification of this phenomenon, and no known site for its origin. Moog et al. have made the assumption that if one finds that chronically distressed patients give a different pain interpretation and response to a physical stimulus, then there must be some central sensitization, particularly as this response seems to affect many body regions. We ask, however, “Where is the centre of this central sensitization?” There is a body of literature showing that if one selects healthy subjects, then makes them anxious and distressed, physical stimuli will be perceived differently and recorded as a more-noxious stimulus than when the same subjects are not distressed (Barsky et al., 1988; Barsky, 1992, 1986; Levine et al., 1982; Robin et al., 1987). Clearly, the healthy subjects of these experiments have no disorder prior to the distress and yet will appear to have the very phenomenon Moog et al. reproduced. Moog et al. note that the group of subjects reporting vibration-induced pain (VIP) used affective pain descriptors more frequently than those who did not report vibration-indicated pain, but that higher psychological scores were not found compared with the other patients. Of course, the patient group tended to be a distressed group, so the overall psychological scores should tend to group them together. Even within the subject group of chronic whiplash, however, those who reported VIP had significantly higher affective but not sensory pain descriptor scores on the short form McGill Pain Questionnaire. Moog et al. found a relatively homogeneous psychological profile. This homogenous psychological profile is thought to be the result of the chronic pain state and not a reflection of primary psychopathology. This is not relevant because it does nothing to negate the possibility that what the researchers observe may still be caused by the elevated psychological distress. The authors further state that patients pursuing personal injury claims did not rate themselves as being significantly more disabled than those without ongoing litigation. They opine that the responses to vibratory stimuli were independent of litigation status. They have made the same error in thinking as Sapir and Gorup (2001) who used facet joint blocks on litigating and non-litigation patients to attempt to show that litigation was irrelevant to treatment outcome: they both failed to recall there are at least 12 other forms of secondary gain besides money, and some other ways of achieving monetary benefits without litigation (Ferrari and Kwan, 2001; Ferrari, 2002). The citation of facet joint studies is even less helpful for reasons explained elsewhere (Kwan and Friel, 2002). It is clear that the presence of psychological distress may be just as valid an explanation for the findings of Moog et al. The study design used by Moog et al. cannot test for the centre of central sensitization, as their control group was wholly inappropriate to address this important question. We suggest, that the “gold standard” in this type of research has already been set and should be followed carefully (Carragee et al., 2000). Carragee et al. accomplished this in a study examining for responses to a noxious stimulus in chronic spinal pain. The results are quite revealing. To explain, Carragee et al. wanted to examine the responses to the noxious stimulus of discography (known to be painful to some extent even in healthy subjects). Discography tends to be painful in chronic low back pain patients, and the question is whether or not the physical cause of the back pain is the cause of the response to discography, or whether the psychological distress of back pain patients is the predictor of the discography response, independent of chronic pain. Carragee et al. chose 3 groups as control subjects: (1) healthy subjects with no low back pain and no psychological distress, (2) subjects with chronic neck pain, but no low back pain, and (3) subjects with chronic anxiety or other chronic psychological distress, but no pain. As expected, the chronic low back pain patients reported more severe and diffuse pain with the injection much more often than the healthy subjects. What was unexpected was that 43% of the subjects with chronic neck pain but no low back pain also reported more severe and diffuse low back pain with the lumbar disc injection. This could mean that chronic neck pain patients with no low back pain share some common features with chronic low back pain patients. To eliminate the factor of chronic pain, one must review the response of the psychologically distressed subjects without pain: 83% had a response just like that of the chronic low back pain patients. Thus, the independent predictor of the painful response to lumbar discography is not the presence or absence of chronic pain, nor necessarily the presence or absence of tissue pathology. The independent predictor of the painful response is the presence or absence of psychological distress. The psychological distress causes what should be a mildly painful stimulus to be registered as more severe and more diffuse (i.e., symptom amplification). In this study it is the psychological construct entitled symptom amplification which is common to the chronic low back pain, chronic neck pain, and psychological-distressed subjects without chronic pain. How does one interpret the results of Moog et al.? Certainly, without a proper control group included in the study it is difficult.

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