Plasma endothelin-1 levels in patients with complex regional pain syndrome

The clinical characteristics of complex regional pain syndrome (CRPS)--spontaneous and stimulus-evoked pain, autonomic abnormalities, motor dysfunction, and trophic changes in the affected limb--are well known. However, its pathogenesis is unclear, and the diagnosis is often delayed, in part due to lack of objective laboratory tests. Endothelin-1 (ET-1) is a potent vasoconstrictor that has recently been shown to produce pain, allodynia, edema, and muscle weakness, as well as to exert a direct excitatory effect on nociceptive afferents. Furthermore, new evidence indicates that ET-1 is involved in various cancer- and non-cancer-related painful conditions. The aim of the present explorative study was to determine the ET-1 plasma levels in patients with CRPS in an attempt to identify a 'laboratory marker' for CRPS and to search for evidence suggesting that ET-1 may be involved in the pathogenesis of CRPS. ET-1 plasma levels were determined in 20 severely affected CRPS patients, in eight patients with non-CRPS chronic painful conditions, and in 10 healthy volunteers. The results showed that there were no significant differences in ET-1 plasma levels between the three groups. We conclude that the plasma level of ET-1 cannot be regarded as a 'marker' for CRPS. Yet, the possibility that ET-1 is involved in the pathophysiology of CRPS has not been excluded and deserves further investigation.