Pressure-induced referred pain as a biomarker of pain sensitivity in fibromyalgia

Background: Fibromyalgia (FM) syndrome is characterized by widespread pain, fatigue, and generalized increased pain sensitivity. Appropriate and simple pain models are methods employed to assess pain mechanisms that can potentially lead to improved treatments. Pressure pain thresholds (PPTs) or mapping the referred pain area produced by pressure stimulation at suprathreshold intensities are used to assess pain mechanisms. The optimal suprathreshold stimulation intensity to elicit referred pain with minimal discomfort for patients with FM has yet to be determined. Objectives: The aim of this study was to compare the area and intensity of pressure-induced referred pain in patients with FM as elicited by systematic increases in PPTs, compared with controls. Study Design: Observational, crossed-section study. Setting: Research laboratory. Methods: Twenty-six patients with FM and 26 healthy controls, age-and gender-matched, were included. Suprathreshold stimulation was applied to the infraspinatus muscle of the dominant side at 4 different intensities (PPT +20%, +30%, +40%, and +50%), after which referred pain was evaluated by measuring the area of pain in pixels using a digital body chart and its intensity on a Visual Analog Scale. Factors related to anxiety condition, pain catastrophizing, depression, and quality of life were recorded. Results: The referred pain areas were larger in the FM group compared with healthy individuals at 120% (P = 0.024), 130% (P = 0.001), 140% (P = 0.001), and 150% (P = 0.001) PPT, however, within the FM group no differences were found between the intensity of suprathreshold stimulation and the size of the referred pain areas (P = 0.135) or pain intensity (P > 0.05). There was a positive correlation between the size of referred pain areas and pain catastrophizing in the FM group (r = 0.457, P = 0.032). Limitations: This study presents some limitations, among which is the variability found in the referred pain areas. Conclusions: These findings show that referred pain induced by applying a suprathreshold pressure of 120% PPT can be a useful biomarker to assess sensitized pain mechanisms in patients suffering from FM