It is not atypical for patients with posttraumatic stress disorder (PTSD) to present with several concomitant physical and mental health problems. These most often include increased reporting of physical symptoms and physical health problems, increased alcohol consumption, and depressed mood (1,2). Recent evidence suggests that pain is one of the most commonly reported symptoms of patients with PTSD, regardless of the nature of their traumatic experience (for example, military combat, motor vehicle accident, or sexual assault). Similarly, patients who have persistent, chronic pain associated with musculoskeletal injury, serious burn injuries, and other pathologies (such as fibromyalgia, cancer, or AIDS) frequently present with symptoms of PTSD. In the past decade, investigation into the relation(s) between PTSD and the experience of pain has flourished. To a lesser degree, researchers have developed models that attempt to explain how the conditions may be linked (3).
This paper has several purposes. First, we provide summary definitions of the conditions under discussion. Second, we highlight symptoms from each condition that have similar characteristics. Third, we summarize the literature on prevalence rates of pain experiences in PTSD populations, and vice versa. Fourth, we articulate potential explanations for the observed association between pain and PTSD. Finally, we discuss future directions for empirical investigation and clinical practice that stem from this line of inquiry.
PTSD typically develops following exposure to a situation or event that is, or is perceived to be, threatening to the well-being of oneself or another person. As presented in the DSM-IV-TR (4), symptoms are grouped into 3 clusters: reexperiencing of the event (for example, intrusive thoughts and nightmares), avoidance and emotional numbing (for example, restricted affect), and hyperarousal (for example, sleep difficulties and hypervigilance). To satisfy criteria for a diagnosis of PTSD, a person must be exposed to a traumatic event with actual or perceived threat. In addition, the individual must experience intense fear or helplessness; must have at least 1 reexperiencing symptom, at least 3 avoidance and numbing symptoms, and at least 2 hyperarousal symptoms; must be bothered by these symptoms for more than 1 month; and must be significantly distressed or impaired in social, occupational, or other functioning. Recent findings indicate that prevalence rates for PTSD in the general population range between 7% and 12% (5); in certain at-risk groups (for example, survivors of sexual assault, motor vehicle accidents, or military combat), the rates can be substantially higher (4).
Accumulating evidence from factor analytic investigations (6–9) suggests that the PTSD symptom clusters outlined in the DSM-IV-TR diagnostic criteria may not best conceptualize PTSD symptom profiles. While the optimal symptom cluster arrangement differs slightly among each of these investigations, a consistent finding is that the 2 elements of the current avoidance and numbing cluster should be considered independently. In short, the empirical evidence suggests that PTSD comprises 4 distinct symptom clusters: reexperiencing, avoidance, numbing, and hyperarousal. Recent treatment studies show that it is important to distinguish among the 4 clusters because important effects of intervention—particularly in the avoidance and numbing domains—are lost if the 4 clusters are not examined separately (10,11). This has not become clinical convention, but as will become evident below, it is an increasingly common consideration in empirical work.
The traditional medical model conceptualizes pain as a pure sensory experience arising from noxious stimulation (for example, organic pathology and physical injury). Contemporary models now recognize that biological, psychological (for example, cognitive, affective, and behavioural), and social factors are involved in the experience (12,13). These contemporary models conceptualize pain as a complex, subjective, perceptual phenomenon involving numerous dimensions (for example, intensity, quality, time course, and personal meaning). Pain is typically acute and occurrs in response to actual or potential tissue damage to motivate adaptive processes that facilitate escape and promote recuperative behaviour (14). However, for about 30% of adults in developed countries, the experience of pain persists over long periods of time, whether it is related to injury or to some organic pathology (15); it often leads to distress, suffering, and functional disability (16,17); and it is associated with inappropriate use of medical services, costly insurance claims, and work absenteeism (18,19). When pain persists for at least 3 months, it is considered chronic (20). Many, but not all, patients with chronic pain exhibit considerable anxiety, avoidance behaviour, and general emotional lability, as well as attentional biases and hypervigilance for pain cues (21). In Canada, chronic musculoskeletal pain is the second most common chronic health condition, costing the health care system approximately $18 billion annually.
A close look at the definitions provided above indicates that there is some degree of symptom overlap between PTSD and chronic pain. In particular, anxiety and hyperarousal, avoidance behaviour, emotional lability, and elevated somatic focus are frequently observed in both conditions. Both PTSD and chronic pain are characterized by hypervigilance (21,22) and attentional bias (23,24) for stimuli that are specific to each condition. There are also data suggesting that startle responses are intensified during states of negative affect (25), to which both conditions can be a major contributor (26). Further, preliminary data suggest that stress responses and pain modulation are dysregulated in both conditions (27,28). Collectively, these findings indicate that PTSD and chronic pain share similar response patterns in the cognitive, behavioural, and physiological domains; in the opinion of some (3,29), the data suggest an intricate connection between the 2 conditions.
One method for gaining preliminary insight into the relation(s) between PTSD and pain—albeit a limited one in that it does not allow for conclusions regarding the nature of the association (see below)—is to assess the degree to which they co-occur. As might be anticipated, based on the preceding discussion, the literature indicates a high degree of co-occurrence, regardless of whether pain is being assessed in patients with PTSD, or vice versa.
Pain in Patients With PTSD
PTSD and PTSD symptoms are associated with greater reporting of physical health problems and symptoms (30–34). They are also strongly associated with current pain, overall pain ratings, and pain-related disability (29,35); with functional impairment (31,32); and with increased health care utilization (36). For military veterans, these findings appear to hold regardless of the theatre (for example, Vietnam or the Persian Gulf) or the nature of the trauma experienced. At the acute level, then, there is evidence suggesting that PTSD symptoms and pain—as well as functional impairments that might be attributed to either or both—frequently co-occur. Does this association hold in cases wherein pain persists beyond the acute phase?
In one of the first studies to assess co-occurrence of PTSD and chronic pain, White and others reported that approximately 1 in 5 military veterans with PTSD developed chronic pain (37). More striking, Beckham and others observed that the symptoms reported by 80% of consecutive outpatient military combat veterans sampled (103/129) satisfied the criteria for current chronic pain in 1 or more sites, including the back in 77% of cases (29). McFarlane and others found that almost one-half of a sample of volunteer firefighters with PTSD reported significant musculoskeletal pain, primarily in the back, compared with 21% of those without PTSD (38). Others (39,40) have noted that between 20% and 30% of individuals from community and mental health outpatient samples with current PTSD report persistent pain symptoms. In a recent large-scale study of community outpatients, PTSD was associated with an increasing number of pain reports over time and an increased risk of somatic symptoms, even after the researchers controlled for comorbid disorders (41).
PTSD in Patients With Chronic Pain
A growing number of studies have shown that PTSD symptoms tend to be elevated in, and to impact on, patients with chronic pain and fibromyalgia (33,39,42–46). Indeed, it appears that between 10% and 50% of patients receiving tertiary care treatment for chronic pain and related conditions have symptoms that satisfy diagnostic criteria for PTSD, compared with approximately 8% of the general population. Benedikt and Kolb, for example, have reported that 10% of a sample of military veterans being treated for chronic pain also satisfied diagnostic criteria for PTSD (47). In a study of patients with chronic musculoskeletal pain associated with work-related injury, we found that 34.7% had symptoms consistent with a diagnosis of PTSD (42). We also noted that a significant number of patients (18.2%) who did not present with full PTSD had symptoms sufficient for clinical attention; that is, they met the criteria for 2 of the 3 PTSD symptom clusters. Even more striking are the various reports from the motor-vehicle accident literature: these indicate that upward of 50% of patients receiving treatment for chronic pain present with co-occurring PTSD (48,49). All these findings are supported by recent data from the National Comorbidity Study indicating that patients with musculoskeletal pain are 4 times more likely to develop PTSD than are those without musculoskeletal pain (50).
It is, however, important in this context to consider the possibility that the observed rates of PTSD may depend partly on the heterogeneous ways in which patients with chronic pain respond to their symptoms and general situation. This heterogeneity can be operationalized using the Multidimensional Pain Inventory (MPI) (51) and an associated empirical clustering procedure called the Multiaxial Assessment of Pain (MAP) (52,53). These tools identify 3 primary subgroups of patients with chronic pain, including 1) those who are adaptive copers (displaying lower pain severity, pain interference, and affective distress), 2) those who are interpersonally distressed (displaying lower perceived social support), and 3) those who are considered dysfunctional (displaying higher pain severity, pain interference, elevated affective distress and fear, and lower activity). As anticipated, we found evidence to support the hypothesis that PTSD is most prevalent in patients with chronic musculoskeletal pain who are classified as dysfunctional, compared with interpersonally distressed or adaptive copers (54). Indeed, we observed that approximately 70% of dysfunctional copers satisfy diagnostic criteria for PTSD, compared with 21% of interpersonally distressed and 35% of adaptive copers. Others have recently reported similar findings (unpublished data).
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