Relationship between pressure pain thresholds and pain ratings in patients with whiplash-associated disorders

Objectives: Increased sensitivity to pressure is commonly associated with painful musculoskeletal conditions, including whiplash-associated disorders (WADs). Pressure pain thresholds (PPTs) close to the site of presumed tissue damage are thought to represent the degree of peripheral nociceptive sensitization. PPTs over healthy tissue, away from the site of injury, are a marker of central nervous system hyperexcitability. There is uncertainty, however, as to what extent does the sensitization of the nociceptive system, whether peripheral or central, contribute to the ongoing, habitual pain experienced by people with WAD. Methods: One hundred patients with WAD were assessed within 4 weeks of their accident and followed after 3 months; 24-hour average neck pain score, PPTs at the cervical spine and tibialis anterior, demographic factors, and psychological measures were collected. Results: Cervical PPT and neck pain score were significantly, but weakly correlated (r=-0.20 to -0.33). There was no significant correlation between tibialis anterior PPT and pain score at any time point (r=-0.01 to -0.21). Regression analyses indicated a strong influence of generalized psychological distress and fear avoidance on the relationship between PPT and pain report. Discussion: The competing explanations for these findings are that either PPTs provide a poor marker of peripheral and central sensitivity or that these processes are only weakly related to the day-to-day pain experienced by patients with WAD. The latter explanation is supported by the confounding effect of psychological factors on pain score.