Dr Andersen is associate professor at Department of Psychology, University of Southern Denmark.

Tonny Elmose Andersen, PhD

Chronic pain is a massive and costly health problem

 and among the main non-fatal causes of years lived with disability worldwide.

 In the United States alone, an estimated 50 million adults are suffering from chronic pain.

 Huge efforts have been made in past decades to better understand, prevent, and treat chronic pain. A common link between chronic pain and posttraumatic stress disorder (PTSD) has emerged as a result of this research. Many individuals with chronic pain suffer from PTSD due to the incidents that caused trauma-related distress, but chronic pain is also commonly found in individuals with PTSD as their primary disorder. Hence, a better understanding of this comorbidity may be important for the treatment of both disorders.

 vary notably due to differences in sampling and assessment tools. Of importance for the interpretation of prevalence rates, many studies rely on fulfillment of diagnostic criteria based on PTSD screening questionnaires. Two recent systematic reviews reported mean-possible PTSD prevalence rates of 11.7% to 19.1% in clinical pain populations, also noting large subgroup differences.

 Similarly, chronic pain complaints are common in patients with a primary diagnosis of PTSD, with prevalence rates estimated to be as high as 80%.

In a recent systematic review of studies on refugees with PTSD, chronic pain complaints were very common. In some studies, almost all participants reported such complaints.

 Furthermore, several studies have found that higher levels of PTSD symptomatology in patients with chronic pain are associated with higher levels of 

, raising the possibility that the conditions not merely coexist, but may influence one another negatively.

Several theoretical possibilities have been put forward to explain the comorbidity of PTSD and pain. These have mainly focused on shared, predisposing vulnerabilities, or on how the conditions may affect one another.

Asmundson et al suggest that underlying predisposing factors or traits cause the development of both PTSD and chronic pain.

 sensitivity (the tendency to respond with fear due to the assumption that [anxiety] symptoms are harmful), may amplify the intensity of the initial emotional response to a traumatic event, thereby increasing the risk of developing either condition.

 Also, other biological and psychological vulnerabilities have been suggested, such as a lowered physiological threshold for alarm responses and feelings of loss of control and unpredictability.

 Vulnerabilities, together with the circumstances of the traumatic event, affect the emotional responses in the encounter and initiate cascades of cognitive bias, hypervigilance, avoidance behavior, autonomic responses, and muscular responsivity.

 A number of vulnerabilities and processes, then, may make an individual more prone to develop the comorbidity following trauma.

Maybe the most-cited model in the field is the Mutual Maintenance Model.

 This model suggests that chronic pain and PTSD maintain and exacerbate one another through 7 mechanisms. Attentional and reasoning biases toward potentially threatening stimuli as well as catastrophizing are suggested to lead to heightened expectations, overestimations, and selective and negative interpretations of both pain-evoking and fear-evoking stimuli. Furthermore, pain may serve as a traumatic cue, evoking fear and PTSD intrusion and hyperarousal, and vice versa. Avoidant coping styles, depressive symptoms, and fatigue are also potentially intertwined and could lead to physical deconditioning, inactivity, disability—all preventing fear extinction. PTSD-related anxiety may also include pain perception directly. Finally, cognitive overload characterizes both conditions, and it leads to limited capacity to employ adaptive coping strategies.

 developed the Perpetual Avoidance Model, which suggests that PTSD symptomatology begins early post-trauma. Here, dysfunctional cognitions, intrusive symptoms, hyperarousal, avoidance behavior, and inactivity all fuel one another in a circular process. The model posits that pain may be initiated or increased as a function of hyperarousal, leading to reinforced fear-avoidance behavior and inactivity. In addition, Jenewein and colleagues argued that fear-learning deficits and impaired capacity to inhibit fear in PTSD may contribute to increased pain perception, pain sensitivity, and fear responses to painful stimuli.

 This idea builds on classical fear conditioning theory, in which fear-learning deficits cause an over-association of pain cues and prevent adaptive safety learning. Incorrect interpretations of bodily symptoms can lead to reinforcement and catastrophizing.

 As a final note, pain issues can also arise due to anxiety-related tensions.

 on pain sensitization, experimental studies find both increased and decreased pain perception, as well as unaltered pain perception.

 While these mechanisms are not fully understood yet, evidence shows that different pain profiles may be related to different PTSD symptoms and coping mechanisms. In a recent review

, PTSD hyperarousal has been associated with increased pain perception and dissociation with decreased pain perception. Also, the nature of the traumatic event may play a role in how PTSD affects pain sensitization. Combat-related PTSD was found to be associated with increased pain thresholds (the level at which a stimulus is experienced as pain), whereas accident-related PTSD was associated with decreased pain thresholds.

Different coping mechanisms may be related to dissociation and derealization. Whereas dissociation can lead to a reduction of conscious attention toward bodily sensations and incoming stimuli such as pain, anxiety and fearful appraisals may lead to attentional bias toward painful stimuli and thereby a decreased pain threshold. Hence, it seems that accident-related trauma is linked to an anxious and sensitizing reaction, whereas combat-related trauma may lead to a dissociative and habituative reaction. While differences in pain processing can be identified in experimental studies, subjective pain reporting most often points in the direction of a more severe symptom profile in relation to pain, disability, and distress when comorbid PTSD and pain persist.

The biological mechanisms behind pain sensitization and the development of chronic pain are complex but include regulatory mechanisms in the hypothalamic-pituitary-adrenal axis, inflammatory processes, immune system suppression, and fatigue.

Also, more complex interpersonal traumas such as physical and emotional abuse associated with war or sexual assault, for example, are of such a pervasive nature that the ability to trust others can be severely damaged, resulting in attachment insecurities that further increase the risk of developing long-term pain problems.

The high co-occurrence of chronic pain and PTSD and their possible entanglement underline the importance of conducting assessment for both PTSD and pain. Unfortunately, symptom overlap between pain and PTSD makes assessment a challenging task. In particular, symptoms related to the DSM-5 PTSD criterion D and criterion E (

) are also very common in individuals who have chronic pain but do nothave PTSD.

 contains items from the PTSD Checklist for DSM-5 (PCL-5) that are prone to misinterpretation. This exemplifies why screening can be a challenge, as individuals who misinterpret these items will sometimes unintentionally inflate their PTSD symptom scores. The key is to distinguish between the patients who feel upset about the consequences of traumatic pain and those who feel highly upset when thinking about the traumatic event itself. For example, negative beliefs about oneself (line 1) are often tied to a guilty conscience about being unable to fulfill one’s obligations due to pain. Loss of interest in activities and feeling cut off from individuals (lines 2 and 3) are often related to no longer being able to participate in sports and hobbies due to pain. Also, almost everyone with chronic pain at times feels irritable and has difficulty concentrating (lines 4 and 5). Similarly, chronic pain causes sleep problems (line 6). The problem is that intrusion symptoms like “feeling very upset when something reminded you of the stressful experience” (which are understood as unique PTSD symptomatology) are sometimes interpreted by patients as being upset when thinking about how pain hinders participating in activities, and not so much as being upset when thinking about the traumatic event itself.

Keeping the aforementioned challenges in mind, there are several PTSD-screening tools (

) that can easily be used. In accordance with the DSM-5, the PCL-5 covers all 20 PTSD symptoms assessed with the diagnostic interview CAPS-5. Also, there are 2 short-form versions (4 and 8 item) of the PCL-5. Another valid brief screening tool for chronic pain is the PTSD-8. The PTSD-8 includes 8 items covering the 3 PTSD symptom clusters of intrusion, avoidance, and hyperarousal (similar to the criteria of ICD-11) and has shown good overall accuracy when compared to a diagnostic interview in chronic pain.

Similarly, there are good and short instruments for pain complaints. Identification of psychological red flags in patients seeking care for musculoskeletal pain problems or PTSD can be useful in treatment planning, as these are often modifiable. 

 presents selected short screening tools for both pain-related problems and PTSD. The selected screening tools are brief, up-to-date, validated tools useful in the context of comorbid PTSD and pain. Of note, for some patient groups psychological disorders may be associated with stigma and may be more difficult to accept. This is important to recognize as it may have significant impact on what patients report to health care professionals, which is important as diagnostics in this area are highly reliant on self-report.

Case example: mutual maintenance mechanisms

“Jane” is a 38-year-old woman. Ever since a severe car crash, her life has not been the same. She has struggled with chronic pain, and she feels worn out and jumpy. Despite her physiotherapist’s best efforts, Jane continues to struggle to engage in the exercise intervention, and she complains about the exercises making her pain worse.

In psychotherapy, she starts to realize that being “worn out” and “jumpy” are related to the PTSD. Several examples of the integration of the conditions become clear to her:

- She often reports that talking about the trauma increases pain intensity.

- She realizes that her struggle to take on physiotherapeutic treatment was not only due to fear of pain and risk of re-injury, but that pain flare-ups return her to the trauma. In this way, her PTSD has made her highly hesitant to engage and made her feel overwhelmed.

- She begins to realize that both pain and PTSD affect her resources, which are split up between them. On days where PTSD symptoms are severe, she has fewer resources to handle pain, which in turn gets worse.

Interventions in these comorbid cases first and foremost need to be biopsychosocial in nature. Unfortunately, there are very few randomized controlled studies that target comorbid PTSD and pain, making it difficult to devise strong recommendations on best treatments for comorbid PTSD and chronic pain. Although there are good evidence-based treatments for each condition, it is still debated whether both conditions need to be targeted sequentially, in parallel, or by an integrated intervention.

If a sequential approach is chosen, it is important to take into consideration which disorder to treat first. As a rule of thumb, the primary disorder needs to be treated first. However, as previously outlined, the untreated disorder may worsen the other; and it is not always evident which disorder is the primary—particularly not in cases where both conditions developed in parallel.

The parallel approach also poses some challenges. If treated by different providers, collaboration and treatment planning can be difficult. Moreover, the clinicians for each disorder need to make sure that the patient has the resources to engage in both treatments. While an integrated intervention may overcome some of these challenges, there is no exact intervention guidelines for how to integrate the interventions.

Evidence points in the direction of integrating cognitive behavior therapy (CBT) techniques in the treatment of comorbid PTSD28 and chronic pain.

 However, one size may not fit all. The complexity of the trauma needs to be considered. In accident-related trauma (in which the primary symptoms may be musculoskeletal pain with elevated levels of arousal, catastrophizing, and pain-related fear avoidance beliefs), the vicious circle maintaining both pain and PTSD symptoms may be interrupted by interventions such as psychologically informed physiotherapy or an intervention with a cognitive behavioral focus on pain management and exposure to feared activities.

 Also, it has recently been shown that early interventions, including targeting PTSD hyperarousal symptoms and pain-related disability with a physiotherapist-led stress inoculation training intervention combined with physiotherapeutic exercise, was effective in reducing pain-related disability compared to exercises alone.

 For more complex interpersonal traumas, or when chronic pain and PTSD have persisted for years, specific and specialized intervention for both PTSD and chronic pain may be necessary for positive outcomes. With that said, the first step is to be aware of this prevalent co-occurrence of pain and PTSD, which requires a proper assessment of both conditions.

Of course, many other frequently comorbid disorders may further muddle the picture, both for assessment and treatment of both pain and PTSD. For example, many studies on PTSD and pain are conducted in military samples, who are also at increased risk of traumatic brain injuries (TBI) of varying severity. This phenomenon also is true for some type of accidents. There are some studies that show veterans with TBI and PTSD report more pain compared to veterans with either TBI or PTSD alone or neither of them.

Chronic pain and PTSD are also associated with suicidal ideation and violent impulses in veterans despite the presence of TBI.

 While this triad remains largely unexplored, some relevant narrative reviews exist, as well as reflections on treatment (eg, Otis and colleagues

Various psychopharmacological agents can be used to treat comorbid PTSD and chronic pain, but there is limited research. Since such a discussion is beyond the scope of this piece, clinicians are encouraged to investigate for themselves.

We hope this article has shed light on the complexity of the comorbidity of chronic pain and PTSD and sparked an interest in some readers to pursue gaining knowledge on this to the future benefit of patients. We encourage clinicians to always have the comorbidity of pain and PTSD in mind when seeing patients with either chronic pain or PTSD, and to be aware of symptom overlap when screening for possible PTSD in chronic pain. Finally, being aware of the nature of the traumatic event is important for treatment planning. If pain and PTSD is due to the same traumatic event, it may be relevant to consider an integrated or parallel treatment, while complex PTSD due to interpersonal trauma or events dating years back in time may require specific trauma-focused intervention in its own.

is assistant professor in a combined position at Department of Psychology, University of Southern Denmark, and at Specialized Hospital for Polio and Accident Victims. 

is associate professor at Department of Psychology, University of Southern Denmark.

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