RSI revisited The paper by Helme et al.’ is considered to be flawed in a number of key respects. Perhaps most importantly of all, the subject sample was not randomised and is best described as biased. Indeed, the subjects who entered the study selected themselves. We are told that despite the fact that the research staff frequently spent between one to two hours discussing the project with potential subjects, less than 25% of those interviewed agreed to participate. This might be considered somewhat unusual given that a group of individuals allegedly with chronic pain ofindeterminate or at best ill-defied cause, were offered the opportunity to participate in a study with the potential to provide diagnostic and therefore potentially therapeutic data from which they might personally benefit. One of course can only speculate on the reasons why more than 75% of those interviewed declined to participate. The other area of criticism is that none of the subjects who entered the study was ever examined. Rather, it was accepted that what they had was ‘Repetitive strain injury’ (RSI) based on ‘an operational definition’which basically translates to diffuse, inexplicable arm pain in an occupational setting. The authors failed to inform the readership whether or not a difference existed in the flare response between the dominant and nondominant upper limb of the control group, if indeed this was sought. This may be relevant given the findings in the subjects. It is also considered that a more appropriate control group would have been individuals with similar psychological disturbances to the RSI group viz anxiety, affective disturbance, illness preoccupation and illness conviction. The authors admit to difficulty in understanding how ‘generalised influences’ (referring to psychological disturbances) ‘could exert opposite effects on the flare response in the unaffected limb when compared to the pain affected limb’ but this is hardly an insurmountable intellectual hurdle. Illness conviction focused on a particular part of the body and/or relative disuse might serve to create a disparity in the manifestation of a local neurogenic reflex. Finally, the authors postulate that the increased flare response apparently observed in the unaffected upper limb in RSI patients might be explained by an attenuation of the vasoconstrictor reflex ‘due to prolonged clinical pain’.The authors offer no explanation why ‘prolonged clinical pain’ might not have caused exactly the same result in the affected limb, notionally the source of the ‘prolonged clinical pain’.. M. AWERBUCH, Director, Pain Management Unit, Memorial Hospital, North Adelaide, Consultant Rheumatologist, SA. LETTERS AND CASE REPORTS

References 1. Helme RD, Le Vasseur SA, Gibson SJ. RSI revisited: evidence for psychological and physiological differences from an age, sex and occupation matched control group. Aust NZ J Med 1992; 22: 23-9.

REPLY In his comments on our recent paper on Repetitive strain injury (RSI),’ Dr Awerbuch has raised a number of important methodological issues which deserve hrther discussion. It was suggested that the study was flawed because no randomisation procedures were utilised and that a high nonparticipation rate (75%) could introduce biases into the sample. Contrary to these suggestions we would contend that it is not ethically appropriate, nor even feasible, to randomise subjects into a control group and a group to experience ‘intractable diffuse upper limb pain’. An alternative design would be a large sample prospective study and such research should certainly be encouraged. However, whether this approach would yield results any different to the present study remains an empirical question. That only 25% of subjects agreed to participate was unfortunate. In our experience a rejection rate of 30-4070is typical, even for controls, when the terms ‘pain’ and ‘medical research’ are mentioned in the same sentence. We suspect that the higher drop out incidence amongst RSI subjects reflects suspicion arising from past medico-legal experiences and because of the enormous amount of negative publicity concerning this condition, particularly at the time the study was undertaken. In these circumstances we have little choice but to acknowledge the response rate (seldom reported in most studies) and bear this fact in mind when reviewing the conclusions. An operational definition of RSI, which included clinical assessment by a GP, was employed in order to obtain the most representative sample and precisely to avoid the introduction of potential experimenter-induced bias. With respect to the other points raised by Dr Awerbuch, it should be noted that there was no difference in flare size between the dominant and non-dominant sides and in any event the proportion of right handed subjects was the same in each group. The inclusion of a control group with affective disturbances was not considered necessary given our previous findings that subjects with high levels of Aust NZ J Med 1992; 22

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