Pain in primary erythromelalgia--a neuropathic component?

Erythromelalgia is a condition characterized by attacks of red, hot, painful extremities with relief of symptoms by cooling and aggravation by warmth. Although the main emphasis has been on pathophysiological mechanisms related to circulatory changes, recent reports have focused on an involvement of efferent small nerve fibers indicating a neuropathic component. Since the symptoms resemble those described in neuropathic pain, we wanted to investigate the possible affection of afferent nerve fibers. Twenty-five patients with primary erythromelalgia were examined by neurological testing, neurography and quantitative sensory testing. Thresholds for heat, cold, heat-pain and cold-pain detection were compared with those of a group of 29 healthy controls. The patients had significantly higher median heat (39.5 (36.1-40.8) and cold (29.3 (27.1-30.8)-detection thresholds at the dorsal aspects of their feet compared to the controls (37.0 (35.4-37.7) and 31.2 (30.3-31.5) respectively). These findings show an impaired small fiber function inside or close to the symptomatic area in this group of erythromelalgia patients. Seven patients had brush-evoked allodynia and fourteen had punctate hyperalgesia inside or close to the symptomatic areas in their feet. When comparing the individual results, there is a tendency to clustering of patients in two separate groups; reduced small fiber input/no hyperalgesia and normal thermal thresholds/hyperalgesia. Our results showing an affection of afferent small nerve fibers together with the nature of the symptoms, suggest that the pain experienced by erythromelalgia patients could have a neuropathic component.