Is multiple chemical sensitivity a learned response? A critical evaluation of provocation studies
|Affiliations:||a PhD C.Psychol. Chartered Health Psychologist. Editor of the ME and CFS References, Teddington, Middx, TW11 9QX|
b Associate Editor, ME and CFS References, Croydon, CR0 6NA, UK
Background. A systematic review of provocation studies concluded that while persons with multiple chemical sensitivities (MCS) react to chemical challenges, these responses occur more often when they can discern differences between active and sham substances. The authors of the review interpreted these findings as evidence that the symptoms may not be specific to the chemical but related to expectations and prior beliefs. Given the complexity of the subject matter, the studies were re-examined using additional criteria.
Results: Our analysis revealed a number of methodological weaknesses which do not appear to have been given due consideration by the authors when interpreting the findings.
Conclusions. In light of these shortcomings, we believe that their conclusions may have over-stated the role of psychological factors in the aetiology of MCS.
|Keywords: Multiple chemical sensitivity; provocation studies|
There are a number of other issues which should be taken into account when interpreting the research. Firstly, can the responses in the laboratory be generalised to symptoms experienced in real life? Secondly, if conditioning was a common phenomenon, would the incidence of MCS not be much higher than it is? Thirdly, not every patient can identify the initiating stimulus and/or a traumatic event, let alone a neutral object which was present in the same physical environment. Many chemicals to which people become sensitive have no odour. Fourthly, in Pavlovian conditioning, the repeated exposure to the conditioned stimulus in the absence of the unconditioned stimulus should lead to the extinction of the conditioned response. In MCS, the 'conditioned responses' are by definition chronic and tend not to extinguish without clinical intervention . Thus as Graveling et al pointed out, the nature and pattern of the elicited responses in experimental situations are not entirely consistent with those reported by patients with MCS . Although it cannot be discounted, conditioning does not seem to offer a substantive model...
Here it is worth considering the findings from another study which was not included in the review. Saito et al investigated 14 patients with strictly-defined MCS, of whom 79% had a psychiatric disorder. None of the 12 healthy controls had a psychiatric diagnosis. They were asked to note any symptoms on an electronic diary, both when they felt unwell and after a beep which sounded at random intervals. They also carried an air sampling pump and were instructed to switch it on when they experienced a hyper-reactivity reaction. Twelve of the patients reported reactions during the week and in all except one, evidence of a "causative" chemical was detected in their pumps. The electronic diaries revealed raised scores for 11 of the 17 symptoms assessed, and on all four mood scales at the time of the exposure but there were no differences between the patients and controls when the participants were assessed at random. Thus people with MCS tested in daily life do not appear to have somatic or psychological symptoms when they are not provoked. The similarity between the groups when the patients were not experiencing a reaction provides further support for the view that MCS is more closely linked to exposure to chemicals than to disorders such as anxiety, somatoform disorders and depression.