For both stimulation modalities, participants were instructed to press a switch when they first perceived pain, and to rate the pain they experienced on a 0-10 scale following each additional stimulus. Standardized questionnaires were used to measure levels of anxiety, anxiety sensitivity, pain catastrophizing, and dissociation. Additionally, information about the experience and intensity of chronic pain was captured for patients in both the PTSD and control groups.

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Results showed that the PTSD group had higher pain thresholds than the control group, and experienced suprathreshold stimuli as more painful. The higher pain thresholds correlated with increased dissociation and reduced anxiety sensitivity, while hyperresponsiveness to pain correlated with reduced dissociation and increased anxiety sensitivity.

The findings indicate that reduced conscious attention towards incoming stimuli, resulting from dissociation, may cause delayed response in pain threshold measurement. Simultaneous biases towards threatening stimuli and decreased inhibition, possibly due to elevated anxiety, could be responsible for intensification of experimental and chronic pain, the authors write.

Mutual Reinforcement of Anxiety and Dissociation

In analyzing the results, the authors suggest that the increased anxiety and dissociation caused by PTSD mutually maintain and reinforce each other.

“Dissociation is manifested in hyposensitivity to threshold (salience) painful stimuli and, in parallel, anxiety sensitivity is manifested in hyperresponsiveness to suprathreshold painful stimuli (via both sensory and affective pathways). In addition, dissociation and anxiety each enable the existence of the opposite pain response (hyperresponsiveness and hyposensitivity, respectively) when their level is reduced,” the authors write.

The authors note that the complex interrelationship between pain hyposensitivity and pain hyperresponsiveness may affect sensory processing, as well as the emotional interpretation and response to painful stimuli. The attentional biases toward threats and anxiety sensitivity associated with PTSD may lead to a heightened perception of pain as threatening, or serve as a reminder of previous trauma. This perception of threat and stress precipitate the dissociation that is characteristic of PTSD, which may lead in turn to delayed or disrupted attention to painful sensations.

 “The authors have found that two aspects of PTSD symptomatology, anxiety sensitivity and dissociation, are particularly associated with reports of higher pain intensity versus a higher threshold for detecting what is painful, respectively,” Randy Roth, PhD, a professor of physical medicine and rehabilitation from the University of Michigan in Ann Arbor, told Clinical Pain Advisor.