title: Comorbidity of postural orthostatic tachycardia syndrome and chronic fatigue syndrome in an Australian cohort.
abstract: 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.
  
  
  METHODS
  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.
authors.affiliation: Department of Genome Biology, The John Curtin School of Medical Research, The Australian National University, Canberra, Australian Capital Territory, Australia.
authors.forename: G K
authors.initials: GK
authors.lastname: Reynolds
authors.forename: D P
authors.initials: DP
authors.lastname: Lewis
authors.forename: A M
authors.initials: AM
authors.lastname: Richardson
authors.forename: B A
authors.initials: BA
authors.lastname: Lidbury
mesh_terms: D000328:Adult; D001315:Australia / Q000453:epidemiology; D001794:Blood Pressure; D015331:Cohort Studies; D015897:Comorbidity; D015673:Fatigue Syndrome, Chronic / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*; D005260:Female; D006339:Heart Rate; D006439:Hemodynamics; D006801:Humans; D008297:Male; D054972:Postural Orthostatic Tachycardia Syndrome / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology*; D011187:Posture; D015995:Prevalence; D013564:Sympathetic Nervous System / Q000503:physiopathology*
keywords: autonomic function; chronic fatigue syndrome; fatigue syndromes; postural orthostatic tachycardia syndrome; standing test