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. KEY WORDS: Referred pain, pain sensitivity, fibromyalgia, central sensitization, suprathreshold, pressure pain threshold, biomarker, facilitated pain mechanisms.

Tactile localization training for pain, sensory disturbance, and distorted body image: a case study of complex regional pain syndrome.

This report presents a case of complex regional pain syndrome. The patient presented with severe pain, sensory disturbance, and distorted body image at the site of initial injury and other body sites. Tactile localization training (TLT) at only the site of initial injury decreased severe pain at the site of initial injury and the secondary affected sites, whereas TLT at secondary affected sites had no effect. These results highlighted the importance of assessing changes in patients' pain processes to determine the part of the body where TLT should be applied.

Psychological factors predict local and referred experimental muscle pain: a cluster analysis in healthy adults.

BACKGROUND: Recent studies suggest an underlying three- or four-factor structure explains the conceptual overlap and distinctiveness of several negative emotionality and pain-related constructs. However, the validity of these latent factors for predicting pain has not been examined. METHODS: A cohort of 189 (99 female, 90 male) healthy volunteers completed eight self-report negative emotionality and pain-related measures (Eysenck Personality Questionnaire - Revised, Positive and Negative Affect Schedule, State-Trait Anxiety Inventory, Pain Catastrophizing Scale, Fear of Pain Questionnaire; Somatosensory Amplification Scale, Anxiety Sensitivity Index and Whiteley Index). Using principal axis factoring, three primary latent factors were extracted: general distress, catastrophic thinking and pain-related fear. Using these factors, individuals clustered into three subgroups of high, moderate and low negative emotionality responses. Experimental pain was induced via intramuscular acidic infusion into the anterior tibialis muscle, producing local (infusion site) and/or referred (anterior ankle) pain and hyperalgesia. RESULTS: Pain outcomes differed between clusters (multivariate analysis of variance and multinomial regression), with individuals in the highest negative emotionality cluster reporting the greatest local pain (p = 0.05), mechanical hyperalgesia (pressure pain thresholds; p = 0.009) and greater odds (2.21 odds ratio) of experiencing referred pain when compared to the lowest negative emotionality cluster. CONCLUSION: Our results provide support for three latent psychological factors explaining the majority of the variance between several pain-related psychological measures, and that individuals in the high negative emotionality subgroup are at increased risk for (1) acute local muscle pain; (2) local hyperalgesia; and (3) referred pain using a standardized nociceptive input.

Clinical outcomes among low back pain consulters with referred leg pain in primary care.

STUDY DESIGN: Merged data from two primary care prospective cohort studies. OBJECTIVE: To compare the clinical course of low back pain (LBP) consulters to primary care with and without self-reported referred leg pain. SUMMARY OF BACKGROUND DATA: In patients with LBP, the presence of leg pain/sciatica is considered a poor prognostic indicator, associated with more severe pain, disability, and time off work. However, questions remain about how best to identify sciatica in primary care and whether self-reported referred leg pain provides a distinct classification for primary care. METHODS: Data from two large prospective cohort studies of consecutive patients consulting with LBP in 13 general practices were merged. Using self-report data patients were divided into three subgroups: (1) those with LBP alone, (2) LBP with referred pain above the knee (LBP + above-knee), and (3) LBP with referred pain below the knee (LBP + below-knee). Unadjusted and adjusted baseline and 6-month follow-up scores on physical, psychological, and social indicators were compared between the groups using multiple regression analysis. RESULTS: Among 1247 consulters the baseline prevalence of cases with LBP alone was 465 (37%), LBP + above-knee was 308 (25%), and LBP + below-knee was 474 (38%). Baseline severity and 6-month outcomes in the consulters with referred leg pain were significantly worse compared to those with LBP alone across a wide range of clinical characteristics, although differences diminished after adjusting for baseline characteristics. CONCLUSION: The clinical course for LBP with self-reported referred leg pain is much worse. However, the fact that differences in outcome were not worse after adjustment suggests that baseline differences in severity and duration of back pain, demographic, and psychological characteristics largely explain the poorer outcomes in patients with referred leg pain. Future research needs to establish if similar results are observed among patients with clinically determined sciatica.