The aim of the present research was to explore the unique and interactive associations of chronic pain, PTSD, and medication use across indices of physical and psychosocial functioning. Patients classified as high-pain in this sample evidenced poorer physical functioning than did those with lower levels of pain irrespective of medication use, medication type, or PTSD status. In contrast, the relationship between opioid use and physical functioning was dependant on PTSD diagnosis. Opioid use was associated with greater physical impairment among patients without PTSD but was unrelated to functioning among those with PTSD. PTSD diagnostic status evidenced no association with physical functioning either among opioid or non-opioid groups. Pain severity was the only significant factor associated with physical functioning within the SSRI and anxiolytic/sedative models although a marginal interaction of PTSD and anxiolytic use was observed.
Pain severity evidenced equally robust associations with psychosocial impairment whereas PTSD demonstrated more broad effects within this domain of functioning. Opioid use again evidenced an interactive association with PTSD whereby use was related to greater psychosocial impairment specifically among patients without PTSD. A diagnosis of PTSD also was associated with greater psychosocial impairment among patients not using opioids. For opioid users, equally poor functioning was observed irrespective of PTSD symptomology. A marginal pain by opioid interaction also emerged whereby high-pain patients using opioids evidenced poorer psychosocial functioning than both high-pain patients without opioids and low-pain patients with opioids. Associations between SSRI use and psychosocial functioning also were marginally dependent on PTSD. Among the subset of individuals not using an SSRI, patients with PTSD evidenced greater psychosocial impairment than did those without PTSD. No other group differences were noted in these analyses. Data pertaining to anxiolytic/sedative use evidenced main effects of pain and of PTSD, but no association was observed between anxiolytics and psychosocial functioning.
The robust associations observed between pain severity and functional impairment in this research are consistent with literature documenting the considerable individual and societal cost of chronic pain internationally (e.g., Blyth et al., 2001
; Duckworth and Iezzi, 2005
; Harstall and Ospina, 2003
; Lynch and Watson, 2006
). As the single largest factor contributing to impairment in this study, these data strongly suggest that pain management should be considered a central component of interventions targeting survivors of traumatic injury.
Regarding effective pain management, these data indicate that PTSD symptomology may be an important consideration in determining treatment modality for individuals with chronic pain. Medication use, across all categories and within both functional domains, failed to demonstrate a relationship with functioning in pain patients with comorbid PTSD. Existing models of PTSD and pain suggest factors that may contribute to the absence of treatment effects in this particular subsample. McLean et al. (2005)
propose a biopsychosocial model whereby neurobiological and psychosocial systems interact to heighten pain processing and perpetuate PTSD symptomology. Others outline behavioral and psychological factors common to both chronic pain and PTSD (e.g., attentional biases, alterations in pain perception, avoidant coping styles) which contribute to stable, mutually reinforcing pathologies (Asmundson et al., 2002
; Sharp and Harvey, 2001
). To date, the potential complications of this comorbidity have not been addressed in research examining pharmacological interventions for either chronic pain or PTSD (e.g., Brady et al., 2000
; Hale et al., 2007
; Marshall et al., 2001
; Webster et al., 2006
). Outcome research targeting the complexities of this comorbidity is needed given the personal and public health costs associated with post-trauma pain and psychopathology.
Observed associations between medication use and functioning failed to provide evidence for therapeutic effects for any pharmacological agent. Opioid use held significant associations with increased
physical and psychosocial impairment in patients without PTSD. Opioid use also was associated with greater psychosocial impairment among patients with high levels of pain. While surprising, these observations are consistent with epidemiological research reporting associations between opioid use and greater pain severity, higher rates of disability, lower rates of employment, and poorer quality of life (Eriksen et al., 2006
). Side effect profiles associated with opioid use – tolerance, physical dependence, cognitive impairment – often are cited as factors contributing to potential decreases in functioning (Ballantyne and Shin, 2008
; Eriksen et al., 2006
). Evidence of paradoxical increases in pain sensitivity associated with opioid use, a condition known as opioid-induced hyperalgesia, also have been reported in both observational and experimental research (Angst and Clark, 2006
). Although causal relationships cannot be attributed within these cross-sectional data, the present research adds to the growing body of literature questioning the utility of opioids in treating chronic, non-malignant pain on a large scale (Ballantyne and Shin, 2008
). Given inconsistent findings regarding their utility over extended periods, potential for reductions in overall functioning, and the increased risk of abuse and dependency within psychiatric samples, health-care professionals may be well served to consider the relative costs and benefits of extended opioid therapy for patients with chronic pain subsequent to traumatic injury.
The relationship between SSRI use and psychosocial functioning also was marginally dependent on the presence or absence of diagnosable PTSD. Interestingly, SSRIs were not associated with improved physical or psychosocial functioning for any patient subsample. It is possible that the benefits associated with SSRIs observed in previous trauma samples (e.g., Brady et al., 2000
; Marshall et al., 2001
; Tucker et al., 2001
) were negated by over-riding physical pain experienced by patients in the current study. Despite limited evidence for a therapeutic effect of these medications, reservations regarding the efficacy of SSRIs are moderated in that SSRIs are generally viewed as comparatively benign medications. Relative to opioid analgesics, SSRIs carry little to no abuse risk with generally tolerable side effect profiles. Further investigation may reveal only limited benefits associated with SSRI use among patients with comorbid pain and PTSD, but the low risk associated with their use should be an important consideration in determining treatment regiments for these patients.
Anxiolytic/sedative medications held a marginal interactive effect with PTSD with respect to physical functioning although post-hoc examination of this interaction revealed no pairwise group differences. Anxiolytics held no association with indices of psychosocial functioning. It is possible, as with the SSRIs, that the potential benefits conferred by these medications may have been lost secondary to the over-riding effects of chronic pain. It is also possible that the heterogeneous collection of medications included in this category masked the effects of any specific agent. Regardless, anxiolytic therapy generally has demonstrated limited efficacy with respect to the treatment of either PTSD (APA, 2004
) or chronic pain (Sanders et al., 2005
). Though sometimes prescribed for symptomatic benefit, the increased risk of abuse and dependence among PTSD samples argues for the judicious use of these medications.
Interpretation of these data should be made within the context of a number of methodological limitations. First, the cross-sectional nature of these data clearly precludes causal inferences regarding the observed relationships. Potentially relevant variables such as severity of physical injury, concurrent non-pain conditions, variations in medication adherence, litigation status, and general patient expectancies all are unmeasured, uncontrolled factors which may significantly influence functioning. Although the present study is constrained by limitations characteristic of observational research, the observed relationships are consistent with existing data and begin to explore a clinically relevant subset of patients that has been overlooked in the pharmacologic literature. These preliminary associations may be useful in developing specific hypotheses regarding the management of comorbid pain and PTSD.
The homogeneity of the present sample also generates concerns regarding generalization of these findings to more diverse patient populations. As with existing research exploring the efficacy of pharmacological interventions for PTSD and chronic pain (e.g., Brady et al., 2000
; Connor et al., 1999
; Jamison et al., 1998
; Markenson et al., 2005
), the present sample was predominantly middle-aged, Caucasian, and female. Ethnic and racial minorities were overrepresented among both non-completers and high-pain patients in the present study, and existing literature suggests that ethnicity may hold relationships both with chronic pain and PTSD (e.g., Edwards et al., 2001
; Green et al., 2004
; Norris, 1992
). Inclusion of more diverse patient samples in future research would provide a means by which to evaluate the generalizability of the present results and to examine the impact of socio-cultural factors on the interface of chronic pain and PTSD.
Finally, the present data are limited to relationships with physical and psychosocial functioning and are unable to address the impact of medications on specific symptomology (e.g., pain severity, anhedonia, insomnia). It is possible, perhaps probable, that medication use is associated with amelioration of symptom level pathology that does not necessarily translate into more general improvements in overall functioning. Controversy regarding appropriate treatment outcome goals (e.g., reduction in symptom severity, increased occupational or interpersonal functioning, reducing ongoing use of health care services) continues in the public health literature and varies largely from discipline to discipline (Clark, 2008
). In practice, these therapeutic objectives likely share some amount of overlap, but generalizations across level of treatment outcome should be made with care.
Despite evidence of a substantial comorbidity between chronic pain and PTSD following traumatic injury, very little is known regarding the effectiveness of pharmacological treatments within this patient population. The present data suggest that pain severity is one of the most salient factors with respect to overall impairment although PTSD appears to moderate the relationship between medication use and patient functioning in some cases. These data also suggest that the associations of PTSD and medication use with impairment may vary across domains of functioning. Given the current state of the literature, few recommendations can be made regarding preferred treatment modalities for individuals with comorbid pain and PTSD. Health care professionals are advised to be aware of the potential complications of this comorbidity and to consider the increased risk inherent to this particular patient group before proceeding with a course of treatment.