Comparison of Activity Limitations/Participation Restrictions Among Fibromyalgia and Chronic Fatigue Syndrome Patients Journal of Chronic Fatigue Syndrome, Vol. 11(4) 2003, pp. 3-18 Jo Nijs, PT, MSc, MT; Peter Vaes, PT, PhD; Neil McGregor, PhD, MDSc; Luc Lambrecht, MD, PhD; Eike Van Hoof, Clin Psych; Kenny De Meirleir, MD, PhD Affiliations: Jo Nijs is affiliated with the Department of Human Physiology, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel (VUB), Belgium, and Postgraduate Education in Manual Therapy, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel (VUB), Belgium. Peter Vaes is affiliated with the Department of Rehabilitation Science and Physical Therapy, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel (VUB), Belgium, and Postgraduate Education in Manual Therapy, Faculty of Medicine and Pharmacy, Vrije Universiteit Brussel (VUB), Belgium. Neil McGregor is affiliated with the Neurobiology Research Unit, Dental Clinical School, University of Sydney, Westmead, New South Wales, Australia. Luc Lambrecht is in private practice for Internal Medicine, Gent, Belgium. Elke Van Hoof is affiliated with the Department of Human Physiology, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel (VUB), Belgium. Kenny De Meirleir is affiliated with the Department of Human Physiology, Faculty of Physical Education and Physical Therapy, Vrije Universiteit Brussel (VUB), Belgium, and the Chronic Fatigue Clinic, Vrije Universiteit Brussel (VUB), Belgium. Address correspondence to: Jo Nijs, Vakgroep MFYS/Sportgeneeskunde, AZ-VUB KRO gebouw-1, Laarbeeklaan 101, 1090 Brussel, Belgium (E-mail: mailto:Jo.Nijs@vub.ac.be). ABSTRACT. Fibromyalgia (FM) and Chronic Fatigue Syndrome (CFS) are related yet overlapping disorders; the current case definitions prohibit a clear-cut differential diagnosis. These diagnostic criteria mainly address the impairment level of the World Health Organization's International Classification of Functioning, Disability and Health. This study aimed at comparing activity limitations and participation restrictions in patients with FM (n = 90) and CFS (n = 47). The Chronic Fatigue Syndrome Activities and Participation Questionnaire (CFS-APQ) was used for assessing functionality in both groups. The convergent validity of the scores obtained with the questionnaire with visual analogue scales for pain, fatigue and concentration was investigated in FM patients, as well as the content validity. No differences in total scores and 25 out of 26 individual items on the CFS-APQ were observed between the 2 groups (independent samples Mann-Whitney U test). This sample of FM patients reported to be more disabled in 'sitting for two hours' as compared to the CFS group (mean scores 3.0 +/- 1.0 and 2.3 +/- 1.0; P = .004). Four hundred and thirty-seven of the 497 (87.9%) responses to the request to list difficult activities matched the content of the CFS-APQ. The overall scores of the CFS-APQ correlated statistically significant in respect to visual analogue scales for pain and concentration (Spearman rho for the total scores ranged between .44 and .49). These data question the disease specificity of the CFS-APQ for CFS, but suggests its applicability in 'the Chronic Pain-Fatigue Syndromes.' The present report provides evidence for both the content and convergent validity of the CFS-APQ in FM patients. KEYWORDS. Fibromyalgia, activities, participation, questionnaire, Chronic Fatigue Syndrome INTRODUCTION Fibromyalgia (FM) and Chronic Fatigue Syndrome (CFS) are related yet overlapping disorders both characterised by sleep impairments, fatigue, headache, muscle and joint aches, swollen and painful lymph nodes, nausea, gastro-intestinal symptoms and neurocognitive disturbances. The severity of the patients' symptomatology appears to be the only differentiating feature, however none of the currently internationally accepted criteria (1-3) stipulate the usage of a severity index. A number of 'chronic fatigued' patients fulfill both the CDC (Centers for Disease Control and Prevention) case definition for CFS and the ACR (American College of Rheumatology) criteria for FM (4-6). Indeed, when comparing these criteria (Table 1), one can only conclude that differentiating these syndromes is nearly impossible. Laylander (1999) suggested to combine FM and CFS into 'chronic pain-fatigue syndromes' (7,8). Remarkably, FM is categorised as a rheumatic disorder, while CFS patients are generally referred to practitioners of internal or neurological medicine. According to the World Health Organisation's International Classification of Functioning, Disability and Health (WHO-ICF: http://www3.who.int/icf/icftemplate.cfm ), the criteria for both CFS and FM mainly address the impairment level. Therefore, CFS and FM patients may differ in activity limitations/participation restrictions. Our group recently developed the Chronic Fatigue Syndrome Activities and Participation Questionnaire (CFS-APQ), a disease specific measure for assessing activity limitations and participation restriction in CFS patients. The way this questionnaire was constructed, based on a literature review and on self-reported activity limitations and participa­tion restrictions of 141 CFS patients (9), substantiates the content validity and disease-specificity of this new measure. In addition, the unidimensionality, test-retest reliability, convergent validity and two different aspects of the content validity have been found to be satisfactory (10). In this study, CFS-APQ data from 90 FM patients and 47 CFS patients were collected and compared. We hypothesised that no major differences in activity limitations/participation restrictions exist between the 2 patient groups, consequently that this new assessment tool might be useful for assessing part of the health status in FM patients as well. Therefore, the content validity and convergent validity of the scores obtained with the CFS-APQ in FM patients were investigated. © 2003 by The Haworth Press, Inc. All rights reserved.