Altered processing of pain-related information in patients with fibromyalgia

Pressure pain thresholds (PPTs) and event-related potentials (ERPs) elicited by emotional words were analyzed in 12 patients with fibromyalgia (FM) and 12 matched healthy subjects. PPTs were assessed at the middle finger of both hands, before and after the experiment. Overall, FM patients and healthy subjects did not differ in PPT. Nevertheless, FM patients as compared with healthy controls were characterized by a significant enhancement of pain sensitivity from the beginning to the end of the experiment indicating a long lasting sensitization due to repeated stimulation. ERPs were recorded during a language decision task where subjects had to react to unpleasant pain-related and emotionally neutral words depending on syntactic or orthographic cues. An emotional category effect was observed on N400 and P300 components of the ERP, indicating that unpleasant words elicited more positive amplitudes than neutral words. A significant group effect was observed on P200 amplitudes, showing reduced amplitudes in FM patients as compared to healthy controls. Furthermore, unpleasant pain-related compared to neutral words triggered significantly enhanced late positive slow waves in healthy controls, while a comparable effect was not found in FM patients. The ERP and PPT data suggest that FM patients are characterized by an altered cognitive processing of pain-related information and by an abnormal adaptation to mechanical pain stimuli, respectively.