Study findings challenge the content validity of the Canadian Consensus Criteria for adolescent chronic fatigue syndrome
- see above for absract & conclusion that CCC patients no different from CFS ones.
Nice idea, shame about the execution
The basic idea of this study is pretty interesting. Take a bunch of broadly defined CFS patients, select from that group those that meet the much tighter Canadian Consensus Criteria, and see if these CCC patients differ on a range of objective measures from the non-CCC patients.
The authors found no significant difference between the two groups (pretty minor cognitive one) and concluded the CCC do not select a group of patients who are different from generic any-definition-will-do CFS patients.
Personally, I think the ability to select patients with different biological characteristics IS a key test any worthwhile case definition must pass. Unfortunately, it seems this test wasn't up to much, because they way they defined CCC is highly suspect - using a questionnaire of their own making without any input from the CCC group.
How ALL patients were defined:
The paper said:
To be included we required only three months of unexplained chronic/relapsing fatigue of new onset, causing disability to a degree that prevented normal school attendance. We did not require that patients met any other accompanying symptom criteria. The referring units were required to confirm that the patient did not have any medical or psychiatric disorder that might explain the fatigue, and that they had not experienced any concurrent demanding life event.
Seems fine as broad CFS definitions go
How CCC patients were defined
This is where it goes wrong
The paper said:
We previously developed a CFS symptom inventory for adolescents, assessing the frequency of 24 common symptoms during the preceding month. Each symptom was rated on a five-point Likert scale, ranging from never/rarely present to present all of the time.
All parts of this worksheet correspond to items in the questionnaire of the present study, and questionnaire results were therefore used to split the CFS patients into one subgroup that satisfied the Canadian Consensus Criteria (Criteria positive group) and one subgroup that did not (Criteria negative group). As a general rule, all symptoms required in the Canadian Consensus Criteria had to be present more than once a week for patients in the Criteria positive group, corresponding to a score of three or higher on the CFS symptom inventory.
Note they don't have any severity score (Leonard Jason has done a lot of work showing how important it is to assess
severity as well as frequency of symptoms - ignoring severity makes the criteria far too lax). And they only looked at symmptoms for the last month, not six months or more.
The paper said:
This study had some limitations. The questionnaire items used to subgroup CFS patients have not been formally validated for this purpose. However, they correspond closely to the ME/CFS clinical diagnostic worksheet (21 - Sharpe et al).
I
’m not sure the authors of the CCC, or case definition experts such as Leonard Jason, would consider a 1991 paper by Michael Sharpe and colleagues (21) a sound basis for diagnosing patients according to the 2003 CCC.
edit: As
Dolphin points out, the paper quotes the wrong reference and so their questionnaire is NOT based on Michael Sharpe's 1991 paper, but on their version of the CCC ME/CFS diagnositc worksheet. However,
as I argue below, this questionnaire is still unvalidated and doesn't look up to the job of accurately diagnosing Canadian criteria ME/CFS (not enough symptoms and ignoring symptom severity).
To recap, the authors diagnosed CCC using an unvalidated questionnaire
based on a 1991 symptom list from Michael Sharpe and colleagues, ignored symptom severity and only considered symptoms over the last month. That doesn't really cut it, so I'm not sure the results of this study tell us very much at all.
However, this is how the authors interpret their study:
Recently, Fink and coauthors provided evidence
that bodily distress disorders, which in their study included CFS, might be regard as one entity instead of separate ones (29). The results of the present study seem to support this view.
Per Fink, for the record.