How are pain and traumatic stress symptoms related in acute whiplash-associated disorders? An investigation of the role of pain-related fear in a daily diary study.

Comorbidity of pain and posttraumatic stress disorder is well recognized, but the reason for this association is unclear. This study investigated the direction of the relationship between pain and traumatic stress and the role that pain-related fear plays, for patients with acute whiplash-associated disorder. Participants (n = 99) used an electronic diary to record hourly ratings of pain, traumatic stress, and fear of pain (FOP) symptoms over a day. Relationships between pain, traumatic stress, and pain-related fear symptoms were investigated through multilevel models including variables lagged by 1 hour. Traumatic stress was associated with previous pain, even after controlling for previous traumatic stress and current pain; current pain was not associated with previous traumatic stress. The relationship between traumatic stress and previous pain became negligible after controlling for FOP, except for traumatic stress symptoms of hyperarousal that were driven directly by pain. Overall, these results support a pain primacy model, and suggest that pain-related fear is important in the maintenance and development of comorbid pain and traumatic stress symptoms. They also confirm that traumatic stress symptoms of hyperarousal are central in this relationship. Differences between this study and others that reported mutual maintenance can be understood in terms of different stages of whiplash-associated disorder and different intervals between repeated measurements. Traumatic stress may affect pain over longer time intervals than measured in this study. Future research could explore how relationships between traumatic stress symptoms, pain, and FOP change over time, and whether previous experiences of traumatic stress influence these relationships.