Comorbidity of postural orthostatic tachycardia syndrome and chronic fatigue syndrome in an Australian cohort

Objective: Patients with chronic fatigue syndrome (CFS) are frequently diagnosed with comorbid postural orthostatic tachycardia syndrome (POTS), suggesting a shared pathogenesis. The aim of this study was to examine the relationship between demographic characteristics, autonomic functioning and fatigue levels amongst CFS patients with and without comorbid POTS. Design and setting: All patients presenting to the CFS Discovery Clinic between 2009 and 2012 completed a 20-min standing task as part of their initial assessment. Heart rate and pulse pressure were recorded at baseline, at 2-min intervals poststanding, at the end of the task and following a recovery period. Average heart rate and pulse pressure variability were calculated from this data. Age, gender, length of illness and self-reported fatigue scores were also recorded. POTS patients were diagnosed by an orthostatic increase in heart rate >30 beats per min, concomitant symptoms of orthostatic intolerance and no orthostatic hypotension. Differences in autonomic functioning between POTS and CFS patients were compared using independent samples t-tests, whilst logistic and linear regressions were performed to examine the contribution of autonomic functioning to task completion and perceived fatigue, respectively. Results: Comorbidity of CFS and POTS (CFS-POTS) was observed in 11% (33/306) of patients. CFS-POTS patients were significantly younger (P < 0.001), had a shorter length of illness (P = 0.034), experienced greater task difficulty (P = 0.002) and were able to stand for significantly shorter periods compared to the CFS-only patients (P < 0.001). CFS-POTS patients experienced significantly lower baseline diastolic blood pressure (P = 0.002), significantly higher heart rate and lower pulse pressures at each standing measurement. Early heart rate changes (P = 0.002) and overall heart rate change (P < 0.001) were significant predictors of completion status, whereas heart rate variability (P < 0.001) and female gender (P < 0.001) were significant predictors of increased perceived task difficulty. Conclusions: Haemodynamic and demographic differences between CFS-POTS and CFS-only patients suggest that the former group reflects a distinct subgroup of the CFS population. The findings highlight the utility of screening younger patients with fatigue for POTS, and identified heart rate variability as an important marker of fatigue for CFS patients in general