Chronic Fatigue Syndrome (CFS) is a disabling state that was defined by a working group in 1994 1. The main components of the definition are fatigue that is not related to exercise and not relieved by rest, and eight accompanying symptoms, of which four must be present. The CFS is incapacitating, with a serious reduction in daily activity.

Several self-rating scales for the presence and severity of fatigue were developed. Of these, the Multidimensional Fatigue Inventory (MFI-20) 2 and the Checklist Individual Strength (CIS-20) 3 were selected by an international CFS study group 4. The same group advised the Medical Outcomes Survey Short-Form-36 (SF-36) as the tool for the assessment of functional impairment. For the presence of the accompanying symptoms of CFS, a symptom checklist developed by the Centers for Disease Control and Prevention was suggested. The MFI-20 and the CIS-20 were developed in the Dutch language and validated. The SF-36 was translated and validated 5. The CDC Symptom Inventory was validated for the English-speaking countries 6. The translation in Dutch was considered necessary for comparison of data in CFS research in the Netherlands and other countries. The objective of the present study was to translate the CDC Symptom Inventory and to validate it for the Dutch speaking population.

The participants in the study were all patients who attended the CFS Center Amsterdam for the first time for diagnosis and treatment of chronic fatigue from August 2005 to August 2006 and their healthy accompanying persons. No investigations were added to the standard diagnostic protocol for new patients in the Center and the accompanying persons were asked to complete the questionnaires only. Accompanying persons who reported fatigue of one month or more, or were ever identified with medical or psychiatric conditions exclusionary for CFS were excluded from the study. All participants gave informed consent for the use of their data for this study.

The CIS-20 is a 20-item self-report instrument that measures 4 dimensions of fatigue: fatigue, concentration, impaired motivation and impaired activity. For clinical assessment of fatigue we used the fatigue and concentration subscales. The CDC Symptom Inventory DLV was used for the assessment of the presence of additional symptoms and their severity. Symptoms were rated as suggested by Wagner et al. 6. We calculated the CDC Symptom Inventory DLV Total Score, the CDC Symptom Inventory DLV Short Form, the CDC Symptom Inventory DLV Case Definition Score and the CDC Symptom Inventory DLV Other Symptoms score as indicated by the authors. The severity of physical impairment was measured with the physical functioning subscale of the SF-36. All healthy controls completed a list of questions about health, medical interventions in the past and drug use. A physical checkup and laboratory data according to the recommendations of Fukuda et al. 1 were obtained from all patients.

Forty-three healthy controls completed the questionnaires. Sixty-one patients fulfilled the Fukuda criteria for chronic fatigue (CF-group) and 78 patients those for chronic fatigue syndrome (CFS-group) (Table 1). The difference between men and women was significant for all scores (Table 2) (Student's t-test P < 0.001). The differences were partially caused by the age distributions that were not the same for men and women in the Control, CF and CFS groups. The difference of the age distribution between the 3 groups was significant for men and women together (Jonckheere-Terpstra Test: P = 0.013). When tested separately the age differences between the 3 groups were neither different for women (Jonckheere-Terpstra Test: P = 0.287) nor for men (Jonckheere-Terpstra Test: P = 0.177). Analysis of covariance, controlling for age and gender, demonstrated significant differences between the three groups [Λ = .165, F (6,174) = 84.7, p < .000]. The analysis for men and women was done separately.

This evaluation of the clinical application of the Dutch translation of the CDC Symptom Inventory shows that it is a reliable tool for the assessment of CFS.

The patients differed in some respects from the population studied by Wagner et al. 6. We analyzed consecutive patients who attended a tertiary care setting during one year and their healthy accompanying relatives and friends. The majority of CFS patients were female, the accompanying friends were male, and the relatives were most often parents, which explains the difference in the male – female ratio and age between the healthy controls and the patients. The gender difference was analyzed and proved relevant for the outcome.

The differences of the populations explain the different results of the analyses in the two studies, but the trend is comparable. The reliability of the scores, expressed as Cronbach's α coefficient was almost identical in the two studies. The relation of the outcome of the CDC Symptom Inventory (DLV) and the SF-36 Physical Functioning score was comparable. The CIS-20 Fatigue and Concentration scores in our analysis were closely related to the CDC Symptom Inventory DLV scores with correlation coefficients that were comparable to the MFI General Fatigue and Mental Fatigue scores in the study of Wagner et al. 6.

We limited the number of tests because of clinical relevance for the patients. More tests would have added little to the clinical diagnosis of CFS.

The Dutch translation of the CDC Symptom Inventory proved to be a reliable tool in the clinical setting of a tertiary care center. The translated version is reliable and the results are comparable to the study of a different population in an English-speaking country. The different response of men and women to the tests warrants further study.

The author(s) declare that they have no competing interests.