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Quick Find Evidence of subgroups Notes on the various criteria Suggested criteria for ME 1999

Evidence of subgroups.

For further information, see: Information on Subgroups.

The requirement to delineate subgroups stems from recommendations made by Fukuda et al 1994. Some are optional, some are not. Researchers in America made a start by separating patients with and without psychiatric disorders (which revealed significant differences, see elsewhere for ref.’s) and between mild/severe, acute and gradual onset (where the differences were interesting, but not all were replicated). Other studies suggest that the following may be separate entities, with their own aetiologies, but this is far from clear because of the failure to take out the patients with post-exertional fatigue (see below). Rationale: Treatment which clears the problem almost totally would suggest that what you’re treating is the cause of CF, not merely a complication. The following need investigation in terms of aetiological status:

CFS due to OP’s, Gulf War service, patients with low cortisol levels (produce of low stress, also found in RA, not yet documented in pure ME), neurally mediated hypotension (smallish subgroup?, particularly youngsters?), vitamin deficiencies (D, B12), Lyme disease, food/gluten sensitivity, subclinical hypothyroidism (conference report, not yet published), primary sleep disorders (research Krupp), and deconditioning (Bazelman et al, suggesting this is a problem in 24% of broadly-defined CFS).

Broadly defined CFS covers more subgroups, particularly people with psychiatric morbidity and lifestyle disorders. Without delineating subgroups, abnormalities as those found in strictly-defined populations are rare (Hassan et al is an exception). It makes no sense to use CDC ‘94 without separating subgroups as advised.

I think there’s a case to be made, particularly in terms of research, to delineate ME (myalgic encephalopathy) from the main group, for those with fatigue linked to minimal exertion (cf. Paul et al for objective evidence). So far, we’ve noticed the similarities with CFS, but overlooked the differences (cf. Costa, Paul, Scholey et al, Goudsmit, Richardson). In short, these suggest major differences on all variables tested compared to studies on CFS. For instance, patients with ME show greater cognitive impairment, normal to high cortisol, hypoperfusion in brainstem (not found by Belgian group in CFS) and they do not adhere to the rigid coping strategies documented by Wessely, Sharpe et al. Komaroff and his team have added an extra criterium to the CDC ‘88 ones which selects people with ME. NB. Theirs was a science-based decision, not a political one!

The other subgroup which might be delineated at this stage is the deconditioned group, who are mildly disabled but take excessive rest (e.g. as in Sharpe’s paper, a Karnofsky score of 60 plus, median 70, but spending an average of 3 days a week in bed.)

This leaves Group 3, the fatigue syndrome of unknown origin, e.g. OP’s, Gulf war, food sensitivities, hypothyroidism, low cortisol, NMH etc. NB. Research might compare this group with ME and decondi-tioned subgroups on parameters like immune status (TGFB, NK activity), hypoperfusion of the brainstem, recovery of muscle strength etc. if there’s a difference, study individual subsets further.

Notes on the various criteria

1. The Oxford criteria have been superseded by the CDC '94 criteria, so should no longer be used. A letter to a medical journal challenged their validity and they were too ambiguous, so different researchers interpreted them in different ways.
   
   
2. The Oxford and CDC '94 criteria select a broader population than the CDC '88 and London criteria. Evidence: Prevalence studies. Less than 1 per 1000 meet the latter two, about 2% meet the former. As several observers have noted, the CDC '94 criteria cannot really distinguish between CFS and depression, so the incidence of clinical depression may be higher in groups selected using CDC '94 than CDC '88.
   
   
3. The CDC '88 and '92 criteria are flawed in that they rely on a number of symptoms, and they count two of those twice. Also, experts have noted that some of the listed symptoms are less common in chronic ME, so they are not suitable for research into this subgroup. They were devised for post-infectious populations, particularly related to EBV.
   
   
4. Research on CFS using CDC '94 and Oxford criteria have found few of the abnormalities (immune and otherwise) documented in ME (London criteria) and CFS (CDC '88).
   
   
5. The literature indicates that until recently, the Harvard researchers used the CDC '88 criteria with an additional requirement, namely, the presence of post-exertional fatigue. The latter is NOT universal in CFS, but it is a distinguishing feature of ME (cf. Paul et al 1999). The Harvard patients appear totally different from those described by Wessely, Sharpe and White using Oxford and CDC '94.
   
   
6. ME requires different criteria because none of the existing ones for CFS insist on the presence of post-exertional fatigue (e.g. it's only an optional requirement in CDC '94). I haven't come across any criticisms of the London criteria for ME. Studies which used the London criteria include Costa et al (who documented the reduced blood flow in the brainstem) and Scholey et al (who found significant cognitive impairment). Ramsay did not devise diagnostic criteria, but he did describe the features of the illness in several articles and a book. The criteria below are a modification of the London criteria, with one addition taken from Ramsay's descriptions.
   
   
7. It’s difficult to draw firm conclusions but the literature suggests that different criteria select different patient groups (research by Natelson’s team and others) . If one is interested in studying general chronic fatigue, the CDC ‘94 criteria will suffice. However, the CDC ‘94 criteria are not specific enough for CFS. For instance, one study assessed 179 HEALTHY adults and found that 15% met the ‘94 criteria for CFS (Cf. Dechene et al, quoted by Jason et al, Clinical Psychology, 1999, 55, 4, 411-424). Jason et al’s own findings also underline the inadequacies of the CDC criteria as they stand. I cannot recommend the stricter CDC ‘88 criteria either, since Komaroff et al’s report on their validity noted that some items ought to be replaced. For ideas on improving the definition of CFS, see the article by Jason et al or the book by Friedberg and Jason (Am. Psychol. Association, 1998)
   If one wants to study ME, only the London criteria or those below are specific enough. The CDC ‘94 criteria are totally unsuitable. (Although it can be interpreted different ways, the criteria actually exclude patients whose fatigue is the result of ongoing exertion. In ME, the ‘fatigue’ is closely linked to exertion.)

    

 

Suggested criteria for ME. 1999:

1. Generalised or localised muscle fatigue following minimal exertion with prolonged recovery time.
2. Neurological disturbances and variable involvement of cardiac and other bodily systems.
3. Impaired circulation (after Ramsay).
4. Marked variability of symptoms in the course of a day and from day to day.
5. An extended relapsing course with a tendency to chronicity.

For research purposes, a minimum duration of six months may help to differentiate ME from more common, transient post-viral syndromes.

EM. Goudsmit 1999
Psychologist/Archivist, London.
 

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