Kennedy G, Spence V, Khan F, Belch JJF
Vascular Diseases Research Unit, The Institute of Cardiovascular Research, Ninewells Hospital and Medical School, Dundee, UK
A previous study has shown increased endothelin-1 (ET-1) levels in patients with a diagnosis of fibromyalgia syndrome (FMS), concluding that this might contribute to some of the apparent vascular disturbances that characterise the syndrome. There is some overlap between the clinical presentation of FMS and other stress-associated disorders including chronic fatigue syndrome (CFS). The aim of present study was to investigate ET-1 levels in CFS.
The study included 47 patients who fulfilled the Centre for Disease Control 1994 criteria for CFS, as well as 34 age and sex-matched healthy controls. Supine blood pressure measurements were obtained after a standard rest period of 20 minutes, and ET-1 levels were measured by ELISA from a morning blood sample.
No differences in plasma ET-1 levels were found between CFS patients and control subjects (p=0.30, unpaired t-test). CFS patients had a mean ET-1 level of 0.49 pg/mL (range 0.11–1.02) and the control group had a mean ET-1 level of 0.44 pg/mL (range 0.16–0.92). In addition, no differences in blood pressure were found between CFS patients and control subjects.
Taken together, these experimental data challenge the concept that CFS and FMS are part of the same spectrum of illness. Normal ET-1 levels in CFS patients in conjunction with a previously-reported enhanced endothelial response to acetylcholine may predispose these patients to abnormal cardiovascular responses to orthostatic challenge.
Endothelin is a substance found in the blood which causes blood vessels to constrict and blood flow to reduce. Normally this activity is balanced by other substances which cause blood vessels to dilate, but in some diseases endothelin levels are high enough to cause disturbances in blood flow.
High endothelin levels have been found in patients with fibromyalgia syndrome and, since there is some overlap in the problems experienced by these individuals and by those with stress-induced conditions such as ME/CFS, we wondered whether ME/CFS patients also have high endothelin levels.
However, we found that endothelin levels were very similar in both ME/CFS patients and healthy controls. This suggests that ME/CFS and fibromyalgia syndrome are not part of the same spectrum of illness.