Nijs and colleagues [1] have found various correlations; however, they have not proven the direction of causation or shown what can be done with the information. As is well known, pain can have a protective effect; conditions involving a lack of sensitivity to pain can cause all sorts of extra complications. Knowledge of why patients with chronic fatigue syndrome (CFS) experience pain following exercise is far from complete. However, studies in recent years such as by Jammes [2] and Sorensen [3] give possible clues that something abnormal biochemically occurs.
The authors found no association between either the current employment rate or the percentage difference between premorbid and current employment rate and either the Pain Catastrophizing Scale, the Beck Depression Inventory score or the SF-36 bodily pain score so none of these can explain the large drop in the employment rate found in the patients in this study and in other studies, suggesting the involvement of an independent variable. The single exercise test methodology used may not find the disease-specific factors associated with the exercise intolerance in CFS; repeat exercise testing such as 24 hours apart “may be necessary to document the atypical recovery response and protracted malaise unique to CFS”[4]. In the world of employment, most jobs do not involve just one intense burst of activity; continuous work, more comparable with repeat exercise testing, is generally required to hold on to a job.
The authors refer to CFS patients supposedly having “personality traits” “involving activity-avoidance.” However studies such as Harvey et al. [5] suggest CFS patients were more active than their contemporaries pre-illness suggesting that if patients avoid activity, it is unlikely to be due to “personality traits.”
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Comment on: Exercise performance and chronic pain in chronic fatigue syndrome: the role of pain catastrophizing. [Pain Med. 2008]
Source: Kindlon T. Response to: exercise performance and chronic pain in chronic fatigue syndrome: the role of pain catastrophizing. Pain Med. 2009 Sep;10(6):1144; author reply 1145-6. doi: 10.1111/j.1526-4637.2009.00690.x. Epub 2009 Sep 9. http://painmedicine.oxfordjournals.org/content/10/6/1144.long (Full article)