Letter to the Editor
Reply to: Chronic fatigue syndrome:
a clinical and laboratory study with a well-matched control group

J of Internal Medicine 2004; 256; 268-269

G. BLEIJENBERG, J. H. H. M. VERCOULEN, J. W. M. VAN DER MEER


How important are symptom criteria in the definition of CFS?

DEAR SIR.
Every statistic method has its limitations and statisticians may have their
preferences. Co-variance analysis is an accepted method in social sciences.

But the main question: does the application of CDC symptom criteria define
a distinct patient population that requires a different approach or
treatment than fatigued patients who do not fulfill the CDC symptom criteria.

We would like to make the following remarks about this question.

The CDC symptom criteria for chronic fatigue syndrome (CFS), the Holmes or
the Fukuda symptoms are mere consensus criteria. This is demonstrated by
the differences between the Holmes criteria (1988) and the Fukuda criteria
(1994). proposed by a different group of experts. Perhaps more important is
that both sets of symptom criteria are un validated.

A next point is that the way these CDC symptom criteria are assessed makes
all the difference. The prevalence of symptoms based on a complaints
probing list is much higher than spontaneously reported symptoms [1]. In
this respect it is a pity that in the CDC definition of CFS it is not
mentioned in what way these symptoms have to be assessed. There are many
indications that CFS can best be seen as a condition at the end of a
continuum. as we have discussed [2] based on two recent studies [3, 4]. The
latter studies show. amongst other things. that after strict application of
the CFS criteria. symptom criteria included. the diagnosis of CFS in the
general population is not a stable condition over time. At one moment,
subjects are at the end of this continuum. fulfilling the criteria for CFS.
and at other moments they shift and do not fulfil the CFS criteria.

Furthermore. Wessely et al. [5] have observed that there is a linear
relationship between the number of symptoms included in the symptom
criteria and the number of other somatic symptoms. This means that there is
no evidence that CDC symptoms are characteristic of CFS.
In our studies we found that it is not specific symptoms which are related
to impairment, but it is merely the fact that patients who report many
symptoms have more concomitant functional impairment than patients who
report few symptoms [1. 6]. irrespective of which symptoms they report,

Last but no least, we have found in our treatment studies that there is no
difference in effect of cognitive behaviour therapy between CFS patients
with four or more symptoms and patients with one to three symptom criteria
[7].

In conclusion. the diagnostic value of the symptom criteria still has to be
demonstrated.

Conflict of interest statement
No conflict of interest was declared.

G. BLEIJENBERG J. H. H. M. VERCOULEN J. W. M. VAN DER MEER University
Medical Centre Nijmegen. Expert Centre Chronic Fatigue. Medical Psychology.
General Internal Medicine. Nijmegen. The Netherlands

References
1 Swanink CMA. Vercoulen ]HMM. Bleijenberg G. Fennis JFM.
Galama JMD. van der Meer JWM. Chronic Fatigue Syndrome; a clinical and
laboratory study with a matched control group. J Intern Med 1995; 237:
499-506.
2 Bleijenberg G. Editorial: chronic fatigue and chronic fatigue syndrome in
the general population. Health Qual Life Outcomes 2003: 1: 52.
3 Solomon I. Nisenbaum R. Reyes M. Papanicolaou D. Reeves W.
Functional status of persons with chronic fatigue syndrome in the Wichita.
Kansas population. Health Qual Life Outcomes 2003: 1: 48.
4 Nisenbaum R. Jonas J. Unger E. Reyes M. Reeves W. A population-based
study of the clinical course of chronic fatigue syndrome. Health Qual Life
Outcomes 2003: 1: 49.
5 Wessely S. Chalder T. Hirsch S. Wallace p. Wright D. Psychological
symptoms. somatic symptoms. and psychiatric disorder in chronic fatigue
syndrome: a prospective study in the primary care setting. Am J Psychiatry
1996: 153: 1050-9.
6 Vercoulen JHMM. Swanink CMA. Galama JMD. Fennis JFM. van der Meer JWM.
Bleijenberg G. Dimensional assessment in chronic fatigue syndrome. J
Psychosom Res 1994: 38: 383-92.
7 Prins JB, Bleijenberg G. Bazelmans E et al. Cognitive behaviour therapy
for chronic fatigue syndrome: A multicentre randomised controlled trial.
Lancet 2001: 357: 841-7.

Correspondence: G. Bleijenberg. University Medical Centre Nijmegen. Expert
Centre Chronic Fatigue. Medical Psychology. General Internal Medicine. PO
Box 9101 6500 Hb Nijmegen. The Netherlands.
(fax: +31 243610041: e-mail: G.Bleijenberg@nkcv.umcn.nl ).


© 2004 Blackwell Publishing Ltd Journal of Internal Medicine 256: 268-269