University Eye Clinic Basel, Mittlere Strasse 91, P.O. Box, CH-4012 Basel, Switzerland
Correspondence to: J. Flammer. E-mail: Josef.Flammer{at}uhbs.ch
SIR, we appreciate the comments by Dr Kennedy and colleagues regarding our report [1] about plasma endothelin-1 levels in fibromyalgia syndrome. The aim of our study was to measure endothelin-1 (ET-1) plasma levels in patients with fibromyalgia syndrome (FMS), and to compare the results with those for healthy controls matched for sex and age. Using a specific radioimmunoassay [2], we found plasma ET-1 levels to be significantly increased in FMS patients when compared with controls (2.74 ± 0.76 pg/ml, range 1.683.95 vs 1.4 ± 0.23 pg/ml, range 0.91.86; P < 0.0001).
Dr Kennedy and colleagues measured plasma ET-1 levels in patients with chronic fatigue syndrome (CFS) by means of ELISA and found the ET-1 levels to be unaltered in their patients. They conclude that these data challenge the concept that CFS and FMS are part of the same spectrum of illness. Their finding is indeed interesting, but it remains unclear to us why these data are in contrast to our data, as we measured plasma ET-1 levels in FMS and not in CFS patients. Moreover, in the Introduction of our report we pointed out a clinical, but not an aetiological, overlap between FMS and CFS.
The results of Dr Kennedy and colleagues lend additional support to the hypothesis that FMS and CFS are aetiologically distinct. However, further research in this field is necessary before firm conclusions can be drawn.
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