It has been suggested that postural orthostatic tachycardia syndrome (POTS) be considered in the differential diagnosis of those with chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). Currently, measurement of haemodynamic response to standing is not recommended in the UK NICE CFS/ME guidelines. Objectives: To determine prevalence of POTS in patients with CFS/ME. Design: Observational cohort study. Methods: Fifty-nine patients with CFS/ME (Fukuda criteria) and 52 age-and sex-matched

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... ontrols underwent formal autonomic assessment in the cardiovascular laboratory with continuous heart rate and beat-to-beat blood pressure measurement (Task Force, CNSystems, Graz Austria). Haemodynamic responses to standing over 2 min were measured. POTS was defined as symptoms of orthostatic intolerance associated with an increase in heart rate from the supine to upright position of >30 beats per minute or to a heart rate of >120 beats per minute on standing. Results: Maximum heart rate on standing was significantly higher in the CFS/ME group compared with controls (106 AE 20 vs. 98 AE 13; P = 0.02). Of the CFS/ME group, 27% (16/59) had POTS compared with 9% (5) in the control population (P = 0.006). This difference was predominantly related to the increased proportion of those in the CFS/ME group whose heart rate increased to >120 beats per minute on standing (P = 0.0002). Increasing fatigue was associated with increase in heart rate (P = 0.04; r 2 = 0.1). Conclusions: POTS is a frequent finding in patients with CFS/ME. We suggest that clinical evaluation of patients with CFS/ME should include response to standing. Studies are needed to determine the optimum intervention strategy to manage POTS in those with CFS/ME.