What is chronic fatigue syndrome? Heterogeneity within an international multicentre study

Objective: We sought to compare the characteristics of patients presenting with chronic fatigue (CF) and related syndromes in eight international cent res and to subclassify these subjects based on symptom profiles. The validi ty of the subclasses was then tested against clinical data. Method: Subjects with a clinical diagnosis of CF completed a 119-item self- report questionnaire to provide clinical symptom data and other information such as illness course and functional impairment. Subclasses were generate d using a principal components-like analysis followed by latent profile ana lysis (LPA). Results: 744 subjects returned complete data sets (mean age 40.8 years, mea n length of illness 7.9 years, female to male ratio 3:1). Overall, the subj ects had a high rate of reporting typical CF symptoms (fatigue, neuropsycho logical dysfunction, sleep disturbance). Using LPA, two subclasses were gen erated. Class one (68% sample) was characterized by: younger age, lower fem ale to male ratio; shorter episode duration; less premorbid, current and fa milial psychiatric morbidity; and, less functional disability. Class two su bjects (32%) had features more consistent with a somatoform illness. There was substantial variation in subclass prevalences between the study centres (Class two range 6-48%). Conclusions: Criteria-based approaches to the diagnosis of CF and related s yndromes do not select a homogeneous patient group. While substratification of patients is essential for further aetiological and treatment research, the basis for allocating such subcategories remains controversial.