Comorbidity in Chronic Fatigue Syndrome/Myalgic Encephalomyelitis: A Nationwide Population-Based Cohort Study

BACKGROUND: Previous studies have shown evidence of comorbid conditions in chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). OBJECTIVE: To estimate the prevalence of comorbidities and assess their associations using a nationwide population-based database of a Spanish CFS/ME cohort. METHOD: A nationally representative, retrospective, cross-sectional cohort study (2008-2015) assessed 1757 Spanish subjects who met both the 1994 Centers for Disease Control and Prevention/Fukuda definition and 2003 Canadian Criteria for CFS/ME. Sociodemographic and clinical data, comorbidities, and patient-reported outcome measures at baseline were recorded. A cluster analysis based on baseline clinical variables was performed to classify patients with CFS/ME into 5 categories according to comorbidities. A multivariate logistic regression analysis was conducted adjusting for potential confounding effects such as age and sex; response and categorical predictor variables were also assessed. RESULTS: A total of 1757 CFS/ME patients completed surveys were collected. We identified 5 CFS/ME clusters: group 1-fibromyalgia, myofascial pain, multiple chemical hypersensitivity, sicca syndrome, epicondylitis, and thyroiditis; group 2-alterations of ligaments and subcutaneous tissue, hypovitaminosis D, psychopathology, ligamentous hyperlaxity, and endometriosis. These 2 subgroups comprised mainly older women, with low educational level, unemployment, high levels of fatigue, and poor quality of life; group 3-with hardly any comorbidities, comprising mainly younger women, university students or those already employed, with lower levels of fatigue, and better quality of life; group 4-poorly defined comorbidities; and group 5-hypercholesterolemia. CONCLUSION: Over 80% of a large population-based cohort of Spanish patients with CFS/ME presented comorbidities. Among the 5 subgroups created, the most interesting were groups 1-3. Future research should consider multidisciplinary approaches for the management and treatment of CFS/ME with comorbid conditions.