CAN THE CHRONIC FATIGUE SYNDROME BE DEFINED BY DISTINCT CLINICAL-FEATURES

To determine whether patients diagnosed as having chronic fatigue synd rome (CFS) constitute a clinically homogeneous class, multivariate sta tistical analyses were used to derive symptom patterns and potential p atient subclasses in 565 patients. The notion that patients currently diagnosed as having CFS constitute a single homogeneous class was reje cted. An alternative set of clinical subgroups was derived. The validi ty of these subgroups was assessed by sociodemographic, psychiatric, i mmunological and illness behaviour variables. A two-class statistical solution was considered most coherent, with patients from the smaller class (27% of the sample) having clinical characteristics suggestive o f somatoform disorders. The larger class (73% of sample) presented a m ore limited combination of fatigue and neuropsychological symptoms, an d only moderate disability but remained heterogeneous clinically. The two patient groups differed with regard to duration of illness, sponta neous recovery, severity of current psychological morbidity, utilizati on of medical services and CD8 T cell subset counts. The distribution of symptoms among patients was not unimodal, supporting the notion tha t differences between the proposed subclasses were not due simply to d ifferences in symptom severity. This study demonstrated clinical heter ogeneity among patients currently diagnosed as CFS, suggesting aetiolo gical heterogeneity. In the absence of discriminative clinical feature s, current consensus criteria do not necessarily reduce the heterogene ity of patients recruited to CFS research studies.