Evidence for acute central sensitization to prolonged experimental pain in posttraumatic stress disorder

Overview: Chronic Pain and Cannabis-Based Medicines

Chronic pain is primarily conceptualized as a disease in its own right when it is associated with emotional distress and functional impairment. Pathophysiologically, dysfunction of the cortico-mesolimbic connectome is of major importance, with overlapping signals in the nociceptive and stress systems. The endocannabinoid system plays an important role in the central processing of nociceptive signals and regulates the central stress response. Clinically, there is moderate evidence that cannabis-based medicines (CBM) can contribute to a significant reduction in pain, especially the associated pain affect, and improvement in physical function and sleep quality in a proportion of patients with chronic pain. The analgesic effect appears to be largely independent of the cause of pain. In this context, CBM preferentially regulates stress-associated pain processing.

Veterans with chronic pain: Examining gender differences in pain type, overlap, and the impact of post-traumatic stress disorder

BACKGROUND

Women are more likely to experience multiple overlapping pain conditions (MOPCs) relative to men. Post-traumatic stress disorder can negatively impact the severity and trajectory of chronic pain and its treatment. Specific associations between gender, post-traumatic stress disorder (PTSD), and MOPCs require further examination.

METHODS

A cohort of all Veterans in 2021 who met criteria for one or more of 12 chronic pain types was created using national Veterans Health Administration administrative data. MOPCs were defined as the number of pain types for which each patient met criteria. Multivariable logistic regression models estimated gender differences in frequency for each of the 12 pain subtypes, after controlling for demographics and comorbidities. Negative binomial regression was used to estimate gender differences in the count of MOPCs and to explore moderation effects between gender and PTSD.

RESULTS

The cohort included 1,936,859 Veterans with chronic pain in 2021, which included 12.5% women. Among those with chronic pain, women Veterans had higher rates of MOPCs (mean = 2.3) relative to men (mean = 1.9): aIRR = 1.31, 95% CI: 1.30-1.32. PTSD also served as an independent risk factor for MOPCs in adjusted analysis (aIRR = 1.23, 95% CI: 1.23-1.24). The interaction term between gender and PTSD was not significant (p = 0.87). Independent of PTSD, depressive disorders also served as a strong risk factor for MOPCs (aIRR = 1.37, 95% CI: 1.36-1.37).

CONCLUSIONS

Individuals with MOPCs and PTSD may have complex treatment needs. They may benefit from highly coordinated trauma-sensitive care and integrated interventions that simultaneously address pain and PTSD.

SIGNIFICANCE

Women were significantly more likely than men to experience MOPCs. PTSD was also significantly, independently, associated with MOPCs. Patients, particularly women, may benefit from tailored interventions that address both trauma and MOPCs.

Continuing Education Intervention: Trauma-Informed Pain Management in Labor and Delivery

BACKGROUND

There is a gap in the availability of continuing education opportunities for labor and delivery nurses regarding trauma-informed perinatal care.

METHOD

A continuing education module on trauma-informed pain management in labor was created and distributed to 17 nurses in an intrapartum unit at a hospital in the Midwestern United States. Changes in knowledge, attitudes, skills, and intent to use trauma-informed principles were assessed using a pretest-posttest design and paired t test analyses.

RESULTS

Change in knowledge (p = .043) and skills (p = .011) was statistically significant. There were no statistically significant changes in attitudes.

CONCLUSION

Continuing education opportunities in trauma-informed perinatal care are needed for health care team members who provide care to trauma survivors in labor. Further research on the effectiveness of trauma-informed pain management in labor and birth is necessary to provide additional resources and recommendations for labor and delivery nurses. [J Contin Educ Nurs. 2024;55(1):21-25.].

Traumatic Events, Posttraumatic Stress Disorder, and Central Sensitization in Chronic Pain Patients of a German University Outpatient Pain Clinic

OBJECTIVE

Posttraumatic stress disorder (PTSD) and traumatic life events are often coupled to chronic pain, possibly linked by central sensitization. We wanted to assess the prevalence of traumatic events and PTSD in chronic pain patients of a German university hospital outpatient pain clinic. Moreover, we evaluated the extent of indicators and co-occurring traits of central sensitization in comorbid patients.

METHODS

We retrospectively divided 914 chronic pain patients into four groups depending on their trauma severity: no trauma, accidental trauma, interpersonal trauma, and PTSD. We collected electronic pain drawings focusing on pain area and widespreadness, as well as information about pain intensity, sleep impairment, disability, stress, anxiety, depression, and somatization. Differences between groups were calculated using Kruskal-Wallis with post-hoc Mann-Whitney tests.

RESULTS

Of 914 patients, 231 (25%) had no trauma, 210 (23%) had accidental traumas, 283 (31%) had interpersonal traumas, 99 (11%) had PTSD, and 91 (10%) could not be classified. We observed statistically significant differences between groups in pain area and widespreadness, as well as maximal pain, sleep impairment, disability, stress, anxiety, depression, and somatization. The severity of symptoms increased with trauma severity.

CONCLUSIONS

Traumatic life events and PTSD are frequent in chronic pain patients. The increased pain area and widespreadness, as well as the increased negative impact on co-occurring traits of sensory sensitivity (anxiety, depression, somatization), are compatible with central sensitization in comorbid patients. Therefore, a heightened awareness of the comorbidity between traumatic experiences and chronic pain is recommended.

Exposure to traumatic events and use of over-the-counter analgesics in adolescents: cross-sectional findings from the Young-HUNT study

OBJECTIVE

Frequent and increasing use of over-the-counter analgesics (OTCA) among adolescents is a public health concern. Prior research indicates that adolescents exposed to traumatic events may be at increased risk of suffering from headaches and musculoskeletal pain. In this study, we assessed the association between trauma exposure and use of OTCA for headaches and musculoskeletal pain.

DESIGN

A cross-sectional population study among adolescents, self-reported data on trauma exposure, pain and use of OTCA.

SETTING AND PARTICIPANTS

All 10 608 adolescents aged 13-19 years in a region of Norway were invited in this school-based survey, participation rate was 76%.

OUTCOME MEASURE

Frequency of OTCA use for headache and musculoskeletal pain served as separate outcomes in ordinal logistic regression analyses.

RESULTS

Trauma exposure was significantly and consistently related to higher frequency use of OTCA for headache and musculoskeletal pain, of which associations for bullying (OR 1.79, 95% CI 1.50 to 2.12, and OR 2.12, 95% CI 1.70 to 2.66), physical violence (OR 1.49, 95% CI 1.25 to 1.78 and OR 1.83, 95% CI 1.45 to 2.32) and sexual abuse (OR 1.83, 95% CI 1.55 to 2.18 and OR 1.53, 95% CI 1.18 to 1.90) were particularly strong. A dose-response relationship was found between interpersonal violence and OTCA use for headache (OR 1.46, 95% CI 1.29 to 1.66 for one type and OR 1.81, 95% CI 1.53 to 2.14 for two or more types) and musculoskeletal pain (OR 1.61, 95% CI 1.91 to 3.00 for one type and OR 2.39, 95% CI 1.91 to 3.00 for two or more types). The associations remained significant after adjustment for pain, although an attenuation in strength was observed.

CONCLUSION

Trauma exposed adolescents use OTCA for headaches and musculoskeletal pain more frequently than those not exposed. The higher frequency of pain conditions among trauma exposed only partially explained their more frequent OTCA use, indicating an increased risk relating to features beyond frequency of pain.

Temporal model for central sensitization: A hypothesis for mechanism and treatment using systemic manual therapy, a focused review

The purpose of this focused review is to develop a consolidated hypothesis as to the causes and mechanisms of central sensitization and a related model for a treatment approach using Systemic Manual Therapy (SMT). The key to understanding central sensitization is a firm grasp on structure and function of the Locus-coeruleus noradrenaline system (LC-NA). This system uses an elaborate switching mechanism to control the level and rate of activation of multiple systems. This review evaluates the mechanisms and temporal relationships behind four components: salient stimuli, threat coding, aberrant afferent input, and oxidative stress. The five-stage temporal model for central sensitization includes phasic activation of the LC-NA system, salient stimuli, threat coding of salient stimuli, central sensitization, and neural degeneration. The three components of treatment include temporarily reducing afferent visceral input, shifting humoral inflammatory activity away from the brain and outside the body, and reducing oxidative stress by making oxygenated blood more available around the LC and other stressed areas in the brain. The SMT protocols that could help in reduction of visceral afferent input are GUOU, Barral and LAUG. Protocols that should shift humoral inflammatory activity away from the brain or completely out of the body include UD and DCS. One protocol that can potentially reduce oxidative stress by making oxygenated blood more available around the LC is CCCV. Future research and hypothesis-testing strategies as well as limitations are further discussed.

Sex and gender differences in pain

Chronic pain affects 20% of adults and is one of the leading causes of disability worldwide. Women and girls are disproportionally affected by chronic pain. About half of chronic pain conditions are more common in women, with only 20% having a higher prevalence in men. There are also sex and gender differences in acute pain sensitivity. Pain is a subjective experience made up of sensory, cognitive, and emotional components. Consequently, there are multiple dimensions through which sex and gender can influence the pain experience. Historically, most preclinical pain research was conducted exclusively in male animals. However, recent studies that included females have revealed significant sex differences in the physiological mechanisms underlying pain, including sex specific involvement of different genes and proteins as well as distinct interactions between hormones and the immune system that influence the transmission of pain signals. Human neuroimaging has revealed sex and gender differences in the neural circuitry associated with pain, including sex specific brain alterations in chronic pain conditions. Clinical pain research suggests that gender can affect how an individual contextualizes and copes with pain. Gender may also influence the susceptibility to develop chronic pain. Sex and gender biases can impact how pain is perceived and treated clinically. Furthermore, the efficacy and side effects associated with different pain treatments can vary according to sex and gender. Therefore, preclinical and clinical research must include sex and gender analyses to understand basic mechanisms of pain and its relief, and to develop personalized pain treatment.

Understanding Pain and Trauma Symptoms in Veterans From Resting-State Connectivity: Unsupervised Modeling

Trauma and posttraumatic stress are highly comorbid with chronic pain and are often antecedents to developing chronic pain conditions. Pain and trauma are associated with greater utilization of medical services, greater use of psychiatric medication, and increased total cost of treatment. Despite the high overlap in the clinic, the neural mechanisms of pain and trauma are often studied separately. In this study, resting-state functional magnetic resonance imaging (rs-fMRI) scans were completed among a diagnostically heterogeneous sample of veterans with a range of back pain and trauma symptoms. Using Group Iterative Multiple Model Estimation (GIMME), an effective functional connectivity analysis, we explored an unsupervised model deriving subgroups based on path similarity in a priori defined regions of interest (ROIs) from brain regions implicated in the experience of pain and trauma. Three subgroups were identified by patterns in functional connection and differed significantly on several psychological measures despite similar demographic and diagnostic characteristics. The first subgroup was highly connected overall, was characterized by functional connectivity from the nucleus accumbens (NAc), the anterior cingulate cortex (ACC), and the posterior cingulate cortex (PCC) to the insula and scored low on pain and trauma symptoms. The second subgroup did not significantly differ from the first subgroup on pain and trauma measures but was characterized by functional connectivity from the ACC and NAc to the thalamus and from ACC to PCC. The third subgroup was characterized by functional connectivity from the thalamus and PCC to NAc and scored high on pain and trauma symptoms. Our results suggest that, despite demographic and diagnostic similarities, there may be neurobiologically dissociable biotypes with different mechanisms for managing pain and trauma. These findings may have implications for the determination of appropriate biotype-specific interventions that target these neurological systems.

Altered physical pain processing in different psychiatric conditions

Several reports indicate either increased or decreased pain sensitivity associated with psychiatric disorders. Chronic pain is highly prevalent in many of these conditions. We reviewed the literature regarding experimental pain sensitivity in patients with major depression, bipolar disorder, posttraumatic stress disorder (PTSD), generalized anxiety disorder, panic disorder, obsessive-compulsive disorder and schizophrenia. Electronic searches were performed to identify studies comparing experimental pain in patients with these conditions and controls. Across 31 depression studies, reduced pain threshold was noted except for ischemic stimuli, where increased pain tolerance and elevated sensitivity to ischemic pain was observed. A more pervasive pattern of low pain sensitivity was found across 20 schizophrenia studies. The majority of PTSD studies (n = 20) showed no significant differences compared with controls. The limited number of bipolar disorder (n = 4) and anxiety (n = 9) studies precluded identification of clear trends. Wide data variability was observed. Awareness of psychiatric patients' pain perception abnormalities is needed for active screening and addressing physical comorbidities, in order to enhance quality of life, life expectancy and mental health.

Can Central Sensitization after injury persist as an autonomous pain generator? - A comprehensive search for evidence

OBJECTIVE

To conduct a comprehensive search for evidence whether Central Sensitization following an injury can act as a persistent autonomous pain generator after the inducing injury has healed.

METHODS

We searched Medline on PubMed and the Cochrane Library, screening 3,572 abstracts, from which 937 full text articles were obtained, with 186 of these discarded as irrelevant to the question being posed. The remaining 751 articles were studied for evidence.

RESULTS

Fourteen publications were judged to provide weak evidence for the hypothesis of central sensitization as a persisting autonomous pain generator, but none addressed the question directly. No strong evidence for the affirmative answer was found.Sixty-two publications were judged to provide weak evidence for a negative answer, and nine judged to provide strong evidence.Unexpectedly, serious weaknesses were discovered in the literature underpinning the validity of the clinical diagnosis of Central Sensitization in man:(i)  Inappropriate extrapolation, in many publications, of laboratory animal data to humans.(ii) Failure to demonstrate the absence of peripheral pain generators which might be perpetuating Central Sensitization.(iii) Many factors now shown to confound what is being measured by quantitative sensory testing, conditioned pain modulation, and Central Sensitization Inventory.

CONCLUSIONS

We found no evidence proving that central sensitization can persist as an autonomous pain generator after the initiating injury has healed.Our review has also shown that the evidential basis for the diagnosis of CS in individual patients is seriously in question.

Widespread Pressure Delivered by a Weighted Blanket Reduces Chronic Pain: A Randomized Controlled Trial

Pleasant sensation is an underexplored avenue for modulation of chronic pain. Deeper pressure is perceived as pleasant and calming, and can improve sleep. Although pressure can reduce acute pain, its effect on chronic pain is poorly characterized. The current remote, double-blind, randomized controlled trial tested the hypothesis that wearing a heavy weighted blanket - providing widespread pressure to the body - relative to a light weighted blanket would reduce ratings of chronic pain, mediated by improvements in anxiety and sleep. Ninety-four adults with chronic pain were randomized to wear a 15-lb. (heavy) or 5-lb. (light) weighted blanket during a brief trial and overnight for one week. Measures of anxiety and chronic pain were collected pre- and post-intervention, and ratings of pain intensity, anxiety, and sleep were collected daily. After controlling for expectations and trait anxiety, the heavy weighted blanket produced significantly greater reductions in broad perceptions of chronic pain than the light weighted blanket (Cohen's f = .19, CI [-1.97, -.91]). This effect was stronger in individuals with high trait anxiety (P = .02). However, weighted blankets did not alter pain intensity ratings. Pain reductions were not mediated by anxiety or sleep. Given that the heavy weighted blanket was associated with greater modulation of affective versus sensory aspects of chronic pain, we propose that the observed reductions are due to interoceptive and social/affective effects of deeper pressure. Overall, we demonstrate that widespread pressure from a weighted blanket can reduce the severity of chronic pain, offering an accessible, home-based tool for chronic pain. The study purpose, targeted condition, study design, and primary and secondary outcomes were pre-registered in ClinicalTrials.gov (NCT04447885: "Weighted Blankets and Chronic Pain"). Perspective: This randomized-controlled trial showed that a 15-lb weighted blanket produced significantly greater reductions in broad perceptions of chronic pain relative to a 5-lb weighted blanket, particularly in highly anxious individuals. These findings are relevant to patients and providers seeking home-based, nondrug therapies for chronic pain relief.

Blunted Pain Modulation Response to Induced Stress in Women with Fibromyalgia with and without Posttraumatic Stress Disorder Comorbidity: New Evidence of Hypo-Reactivity to Stress in Fibromyalgia?

There is evidence regarding the presence of alterations in both the stress response and the endogenous pain modulation systems of people with fibromyalgia (FM). However, research on pain modulation under induced stress on FM patients is scarce and contradictory. The present study analyzes stress-induced changes in pain and intolerance thresholds among FM patients, examining the possible existence of differences linked to PTSD comorbidity and gaining insights into the role of cardiovascular reactivity. Eighteen women diagnosed with FM and comorbid PTSD (FM + PTSD), 18 women diagnosed with FM and no PTSD (FM-PTSD), and 38 healthy women (HC) were exposed to the Social Stress Test task. Pressure pain thresholds and intolerance thresholds were measured before and during stress induction, and after a recovery period, while systolic blood pressure and heart rate were simultaneously recorded. Overall, while pain thresholds decreased during stress and recovery for HC, no significant changes were observed for women with FM. The intolerance threshold decreased for HC during stress, but was maintained at basal level during recovery. FM-PTSD women exhibited a delayed response, with a drop at recovery. For FM + PTSD, tolerance levels remained unchanged. In addition, cardiovascular reactivity did not seem to explain these results. This performance of the pain modulation system seems to follow the same pattern of hypoactive responsiveness under stressors that has previously been observed in FM patients on the autonomic and neuroendocrine axes. Such a hypoactive pattern may involve a non-adaptive response that may contribute to the development and maintenance of chronic pain.

Pain and Trauma: The Role of Criterion A Trauma and Stressful Life Events in the Pain and PTSD Relationship

Chronic pain and post-traumatic stress disorder (PTSD) frequently co-occur, and research suggests that these 2 conditions exacerbate one another producing greater impact on normal functioning in combination than separately. The influence of traumatic experiences on both pain and PTSD has been shown, but the nature of this interplay remains unclear. Although Criterion A trauma is required for the diagnosis of PTSD, whether the association between PTSD and chronic pain is dependent on Criterion A is underexplored. In this observational cohort study, we examined the association between pain and PTSD-like symptoms in the context of Criterion A trauma in 5,791 men from the Vietnam Era Twin Registry. Correlations and mixed-effects regression models were used to evaluate the relationship between PTSD Checklist-Civilian Version symptoms and multiple indicators of pain from the Short Form McGill Pain Questionnaire across trauma history and chronic pain conditions. 53.21% of the participants experienced trauma consistent with DSM-IV Criterion A for PTSD. The associations between pain indicators and PTSD-like symptoms was stronger for individuals with a history of trauma but remained robust for individuals without trauma history. Small but significant interactions between past trauma and pain indicators and PTSD-like symptoms were observed. Findings were similar in a subsample of participants with history of chronic pain conditions. The relationship between PTSD-like symptoms and indicators of pain were largely independent of trauma consistent with Criterion A, highlighting the need to better understand and address stressful life events in chronic pain patients and pain concerns in individuals reporting trauma. PERSPECTIVE: This article demonstrates that the relationship between PTSD-like symptoms and indicators of pain is largely independent of trauma consistent with Criterion A. This finding highlights the need to better understand and address stressful life events in chronic pain patients and pain concerns in individuals reporting trauma.

Posttraumatic Stress Disorder and Chronic Pain Conditions in Men: A Twin Study

OBJECTIVE

Posttraumatic stress disorder (PTSD) is highly comorbid with chronic pain conditions that often co-occur such as migraine headaches, temporomandibular disorder, irritable bowel syndrome, fibromyalgia, chronic fatigue syndrome, chronic prostatitis/chronic pelvic pain syndrome, and tension headaches. Using a genetically informative sample, the current study evaluated the genetic and environmental factors contributing to the co-occurrence of PTSD and chronic pain conditions.

METHODS

Data from 4680 male twins in the Vietnam Era Twin Registry were examined. Biometric modeling was used to estimate genetic and environmental variance components and genetic and environmental correlations between PTSD and multiple chronic pain conditions.

RESULTS

Heritabilities were estimated at 43% (95% confidence interval [CI] = 15%-63%) for PTSD and 34% (95% CI = 27%-41%) for the combined history of any one or more pain condition. Specific pain condition heritabilities ranged from 15% (95% CI = 0%-48%) for tension headaches to 41% (95% CI = 27%-54%) for migraine headaches. Environmental influences accounted for the remaining variance in pain conditions. The genetic correlation between PTSD and combined history of any one or more pain condition was rg= 0.61 (95% CI = 0.46-0.89) and ranged for individual pain conditions from rg= 0.44 (95% CI = 0.24-0.77) for migraine headache to rg= 0.75 (95% CI = 0.52-1.00) for tension headaches.

CONCLUSIONS

PTSD and chronic pain conditions are highly comorbid, and this relationship can be explained by both genetic and environmental overlap. The precise mechanisms underlying these relationships are likely diverse and multifactorial.

Convergent Validity of the Central Sensitization Inventory in Chronic Whiplash-Associated Disorders; Associations with Quantitative Sensory Testing, Pain Intensity, Fatigue, and Psychosocial Factors

OBJECTIVE

Central sensitization is present in different pain conditions, including chronic whiplash-associated disorders. In the absence of a gold standard method of assessment to determine the presence of central sensitization, quantitative sensory testing is currently understood as an optimal proxy. Laboratory sensory testing is, however, not feasible in clinical practice, and the Central Sensitization Inventory was developed as an alternative. The aim of the current study was to evaluate the convergent validity of the Central Sensitization Inventory in chronic whiplash-associated patients by determining the association between the Central Sensitization Inventory and quantitative sensory testing, pain intensity, fatigue, and psychosocial factors.

METHODS

A total of 125 chronic whiplash-associated patients completed multiple questionnaires and were subjected to pressure pain thresholds and temporal summation.

RESULTS

. The Central Sensitization Inventory showed a strong association with constructs of general psychopathology, anxiety, distress, depression, and somatization in chronic whiplash-associated disorders. Moderate correlations were found with fatigue and intrusive and avoidant phenomena after a variety of traumatic events. No significant association was found between the Central Sensitization Inventory and pressure pain thresholds and temporal summation, nor between the Central Sensitization Inventory and other pain measurements.

CONCLUSIONS

Overall, we found that the Central Sensitization Inventory is better in identifying the psychosocial factors related to central sensitization in chronic whiplash-associated disorders than the central nervous system adaptations. Thus, the convergent validity of the Central Sensitization Inventory appears to be only partially present in chronic whiplash-associated disorders.

Factors Associated With Posttraumatic Stress Disorder Among Veterans of Recent Wars Receiving Veterans Affairs Chiropractic Care

OBJECTIVES

Post-traumatic stress disorder (PTSD) is thought to complicate pain management outcomes, which is consistent with the impact of other psychosocial factors in the biopsychosocial model of pain. This study aimed to identify patient sociodemographic and clinical characteristics associated with PTSD prevalence among veterans of Operations Enduring Freedom/Iraqi Freedom/New Dawn (OEF/OIF/OND) who received Veterans Affairs (VA) chiropractic care.

METHODS

A cross-sectional analysis of electronic health record data from a national cohort study of OEF/OIF/OND veterans with at least 1 visit to a VA chiropractic clinic from 2001 to 2014 was performed. The primary outcome measure was a prior PTSD diagnosis. Variables including sex, race, age, body mass index, pain intensity, alcohol and substance use disorders, and smoking status were examined in association with PTSD diagnosis using logistic regression.

RESULTS

We identified 14,025 OEF/OIF/OND veterans with at least 1 VA chiropractic visit, with a mean age of 38 years and 54.2% having a diagnosis of PTSD. Male sex (adjusted odds ratio [OR] = 1.23, 95% CI = 1.11-1.37), younger age (OR = 0.99, CI = 0.98-0.99), moderate-to-severe pain intensity (numerical rating scale ≥ 4) (OR = 1.72, CI = 1.59-1.87), body mass index ≥ 30 (OR = 1.34, CI = 1.24-1.45), current smoking (OR = 1.32, CI = 1.20-1.44), and having an alcohol or substance use disorder (OR = 4.51, CI = 4.01-5.08) were significantly associated with a higher likelihood of PTSD diagnosis.

CONCLUSION

Post-traumatic stress disorder is a common comorbidity among OEF/OIF/OND veterans receiving VA chiropractic care and is significantly associated with several patient characteristics. Recognition of these factors is important for the appropriate diagnosis and management of veterans with PTSD seeking chiropractic treatment for pain conditions.

Repeated exposure of naïve and peripheral nerve-injured mice to a snake as an experimental model of post-traumatic stress disorder and its co-morbidity with neuropathic pain

Confrontation of rodents by natural predators provides a number of advantages as a model for traumatic or stressful experience. Using this approach, one of the aims of this study was to investigate a model for the study of post-traumatic stress disorder (PTSD)-related behaviour in mice. Moreover, because PTSD can facilitate the establishment of chronic pain (CP), and in the same way, patients with CP have an increased tendency to develop PTSD when exposed to a traumatic event, our second aim was to analyse whether this comorbidity can be verified in the new paradigm. C57BL/6 male mice underwent chronic constriction injury of the sciatic nerve (CCI), a model of neuropathic CP, or not (sham groups) and were submitted to different threatening situations. Threatened mice exhibited enhanced defensive behaviours, as well as significantly enhanced risk assessment and escape behaviours during context reexposure. Previous snake exposure reduced open-arm time in the elevated plus-maze test, suggesting an increase in anxiety levels. Sham mice showed fear-induced antinociception immediately after a second exposure to the snake, but 1 week later, they exhibited allodynia, suggesting that multiple exposures to the snake led to increased nociceptive responses. Moreover, after reexposure to the aversive environment, allodynia was maintained. CCI alone produced intense allodynia, which was unaltered by exposure to either the snake stimuli or reexposure to the experimental context. Together, these results specifically parallel the behavioural symptoms of PTSD, suggesting that the snake/exuvia/reexposure procedure may constitute a useful animal model to study PTSD.

Evaluation of Candidate Items for Severe PTSD Screening for Patients With Chronic Pain: Pilot Data Analysis With the IRT Approach

OBJECTIVES

Post-traumatic stress disorder (PTSD) commonly co-occurs with chronic pain. Although PTSD symptoms are associated with negative health outcomes in patients with chronic pain, PTSD is typically under-detected and under-treated in outpatient pain settings. There is a need for rapid, brief screening tools to identify those at greatest risk for severe PTSD symptoms. To achieve that goal, our aim was to use item response theory (IRT) to identify the most informative PTSD symptoms characterizing severe PTSD in patients with chronic pain.

METHODS

Fifty-six patients (71% female, 61% White) with mixed etiology chronic pain completed the PTSD Checklist-Civilian Version (PCL-C) as part of their appointment with a pain psychologist at a tertiary outpatient pain clinic. We used an IRT approach to evaluate each item's discriminant (a) and severity (b) parameters.

RESULTS

Findings revealed that "feeling upset at reminders" (a = 3.67, b = 2.44) and "avoid thinking or talking about it" (a = 3.61, b = 2.17) as being highly discriminant for severe PTSD.

CONCLUSIONS

We identified 2 candidate items for a brief PTSD screener as they were associated with severe PTSD symptoms. These 2 items may provide clinical utility in outpatient pain treatment settings to identify those suffering from severe PTSD, enabling physicians to refer them to trauma-specific evaluation or therapy. Future research is needed to further validate and confirm these candidate PTSD items in a larger clinic sample.

LAY SUMMARY

The current study used the IRT approach to identify candidate items for a brief screener for severe PTSD. We examined 17 items of the PCL-C, and identified 2 items that were highly discriminant for severe PTSD. The 2 items were "feeling upset at reminders" and "avoid thinking or talking about it." These 2 items may provide clinical utility, since they may enable physicians to screen and make a referral for further assessment or treatment for PTSD.

Development of a pain neuroscience education program for post-traumatic stress disorder and pain

Introduction: Individuals with co-morbid post-traumatic stress disorder (PTSD) and pain have higher disability, pain, and pain catastrophizing beliefs than patients without PTSD. Pain neuroscience education (PNE) may be an effective tool to help those with PTSD and pain reduce maladaptive beliefs about pain. The purpose of this paper is to report the development and evaluation of a PNE curriculum for participants with PTSD and pain. Methods: After writing an initial draft of PNE for PTSD and pain, a panel of medical experts in PNE, PTSD, and rehabilitation reviewed the booklet. After addressing recommendations from the medical panel (n = 29), individuals with (n = 13) and without (n = 20) PTSD reviewed the booklet. Results: Overall, 89% of participants recommended the PNE booklet and 90% thought it would help patients with PTSD and pain. Although patients with PTSD rated the PNE booklet more critically than other participants, a particular support group (n = 4) rated the PNE booklet significantly different (p < .05) than remaining participants with PTSD (n = 9). Individuals with PTSD and pain were able to comprehend the PNE booklet at a comparable rate to an expert medical panel and participants without PTSD after adjusting for education levels (p = .12). Conclusions: Many patients with PTSD and pain avoid painful activities because they believe they are harmful. This research demonstrates that individuals with PTSD and pain can comprehend PNE that challenges these beliefs. The PNE curriculum developed by this research may provide a logical explanation for the link between PTSD symptoms and pain and should be tested for clinical effectiveness.

Chronic pain intervention using pulsed shortwave therapy: the relationship between pain demographics and central sensitization inventory

Aim: The central sensitization inventory (CSI) is a validated, patient-reported questionnaire that quantifies symptoms of hypersensitivity disorders such as chronic pain, for which central sensitization (CS) may be the etiology. Objective: To investigate the analgesic effectiveness of ActiPatch and analyze the relationship between baseline CSI scores and demographics of chronic pain sufferers. Methods: Upon completing a 7-day ActiPatch trial, baseline CSI scores along with other assessment measures were obtained via e-mail from 174 chronic pain sufferers. Conclusion: CSI scores were positively correlated with gender (higher for women), baseline visual analog scale scores and pain duration. ActiPatch was found to be effective in reducing baseline pain for all subjects by an average of 4.3 visual analog scale points.

Posttraumatic Stress Symptoms Mediate the Effects of Trauma Exposure on Clinical Indicators of Central Sensitization in Patients With Chronic Pain

OBJECTIVE

Evidence supports high rates of co-occurrence of posttraumatic stress disorder (PTSD) and chronic pain disorders involving central sensitization (CS). The nature of this relationship, however, remains relatively unexplored. In this study, we aimed to (1) assess how both trauma exposure and current PTSD symptoms are related to clinical manifestations of CS, and (2) test whether PTSD symptoms explain the relationship between trauma exposure and CS. Because experiential avoidance has been shown to impact the relationship between trauma and health outcomes, we (3) explored experiential avoidance as a possible mediator or moderator of the trauma-CS relationship.

METHODS

A sample of 202 adult patients (79% female) with chronic pain completed validated self-report measures of trauma exposure, current PTSD symptoms, experiential avoidance, and 3 manifestations of CS: widespread pain, greater pain severity, and polysomatic symptom reporting. We used path analysis and multivariate regression to assess our study aims.

RESULTS

Both trauma exposure and PTSD symptoms were significantly associated with all 3 clinical indicators of CS. PTSD symptoms partially explained the relationship between trauma exposure and widespread pain, pain intensity, and polysomatic symptoms. Experiential avoidance did not mediate or moderate the trauma-CS relationship.

CONCLUSIONS

Our findings suggest that trauma exposure is linked to elevated clinical markers of CS but a critical factor in this relationship is the mediating effect of current PTSD symptoms.

Race/Ethnicity Does Not Moderate the Relationship Between Adverse Life Experiences and Temporal Summation of the Nociceptive Flexion Reflex and Pain: Results From the Oklahoma Study of Native American Pain Risk

Adverse life experiences (ALEs) are associated with hyperalgesia and chronic pain, but the underlying mechanisms are poorly understood. One potential mechanism is hyperexcitability of spinal neurons (ie, central sensitization). Given that Native Americans (NAs) are more likely to have ALEs and to have a higher prevalence of chronic pain, the relationship between ALEs and spinal hyperexcitability might contribute to their pain risk. The present study assessed temporal summation of the nociceptive flexion reflex (TS-NFR; a correlate of spinal hyperexcitability) and pain (TS-Pain) in 246 healthy, pain-free non-Hispanic whites and NAs. The Life Events Checklist was used to assess the number of ALEs. Multilevel growth models were used to predict TS-NFR and TS-Pain, after controlling for age, perceived stress, psychological problems, negative and positive affect, and painful stimulus intensity. ALEs and negative affect were significantly associated with greater pain, but not enhanced TS-Pain. By contrast, ALEs were associated with enhanced TS-NFR. Race did not moderate these relationships. This finding implies that ALEs promote hyperalgesia as a result of increased spinal neuron excitability. Although relationships between ALEs and the nociceptive flexion reflex/pain were not stronger in NAs, given prior evidence that NAs experience more ALEs, this factor might contribute to the higher prevalence of chronic pain in NAs. PERSPECTIVE: This study found a dose-dependent relationship between ALEs and spinal neuron excitability. Although the relationship was not stronger in NAs than non-Hispanic whites, given prior evidence that NAs experience more ALEs, this could contribute to the higher prevalence of chronic pain in NAs.

Reward and aversion processing in patients with post-traumatic stress disorder: functional neuroimaging with visual and thermal stimuli

In patients with post-traumatic stress disorder (PTSD), a decrease in the brain reward function was reported in behavioral- and in neuroimaging studies. While pathophysiological mechanisms underlying this response are unclear, there are several lines of evidence suggesting over-recruitment of the brain reward regions by aversive stimuli rendering them unavailable to respond to reward-related content. The purpose of this study was to juxtapose brain responses to functional neuroimaging probes that reliably produce rewarding and aversive experiences in PTSD subjects and in healthy controls. The stimuli used were pleasant, aversive and neutral images selected from the International Affective Picture System (IAPS) along with pain-inducing heat applied to the dorsum of the left hand; all were administered during 3 T functional magnetic resonance imaging. Analyses of IAPS responses for the pleasant images revealed significantly decreased subjective ratings and brain activations in PTSD subjects that included striatum and medial prefrontal-, parietal- and temporal cortices. For the aversive images, decreased activations were observed in the amygdala and in the thalamus. PTSD and healthy subjects provided similar subjective ratings of thermal sensory thresholds and each of the temperatures. When 46 °C (hot) and 42 °C (neutral) temperatures were contrasted, voxelwise between-group comparison revealed greater activations in the striatum, amygdala, hippocampus and medial prefrontal cortex in the PTSD subjects. These latter findings were for the most part mirrored by the 44 vs. 42 °C contrast. Our data suggest different brain alterations patterns in PTSD, namely relatively diminished corticolimbic response to pleasant and aversive psychosocial stimuli in the face of exaggerated response to heat-related pain. The present findings support the hypothesis that brain sensitization to pain in PTSD may interfere with the processing of psychosocial stimuli whether they are of rewarding or aversive valence.

Chronic Pain Types Differ in Their Reported Prevalence of Post -Traumatic Stress Disorder (PTSD) and There Is Consistent Evidence That Chronic Pain Is Associated with PTSD: An Evidence-Based Structured Systematic Review

Objectives

The hypotheses of this systematic review were the following: 1) Prevalence of post-traumatic stress disorder (PTSD) will differ between various types of chronic pain (CP), and 2) there will be consistent evidence that CP is associated with PTSD.

Methods

Of 477 studies, 40 fulfilled the inclusion/exclusion criteria of this review and were grouped according to the type of CP. The reported prevalence of PTSD for each grouping was determined by aggregating all the patients in all the studies in that group. Additionally all patients in all groupings were combined. Percentage of studies that had found an association between CP and PTSD was determined. The consistency of the evidence represented by the percentage of studies finding an association was rated according to the Agency for Health Care Policy and Research guidelines.

Results

Grouping PTSD prevalence differed ranging from a low of 0.69% for chronic low back pain to a high of 50.1% in veterans. Prevalence in the general population with CP was 9.8%. Of 19 studies, 16 had found an association between CP and PTSD (84.2%) generating an A consistency rating (consistent multiple studies). Three of the groupings had an A or B (generally consistent) rating. The veterans grouping received a C (finding inconsistent) rating.

Conclusion

The results of this systematic review confirmed the hypotheses of this review.

Validation of the Japanese version of the Central Sensitization Inventory in patients with musculoskeletal disorders

Background

Many musculoskeletal pain conditions are characterized by hypersensitivity, which is induced by central sensitization (CS). A questionnaire, the Central Sensitization Inventory (CSI), was recently developed to help clinicians identify patients whose presenting symptoms may be related to central sensitivity syndrome (CSS). The aims of the present study were to examine criterion validity and construct validity of the Japanese version of the CSI (CSI-J), and to investigate prevalence rates of CS severity levels in patients with musculoskeletal disorders.

Methods

Translation of the CSI into Japanese was conducted using a forward-backward method. Two hundred and ninety patients with musculoskeletal pain disorders completed the resultant CSI-J. A subset of the patients (n = 158) completed the CSI-J again one week later. The relationships between CSI and clinical symptoms, EuroQol 5-dimension (EQ-5D) and Brief Pain Inventory (BPI), were examined for criterion validity. EQ-5D assesses Health-related QOL and BPI measures pain intensity and pain interference. The psychometric properties were evaluated with analyses of construct validity, factor structure and internal consistency, and subsequently investigate the prevalence rates of CS severity levels.

Results

The CSI-J demonstrated high internal consistency (Cronbach’s α = 0.89) and test-retest reliability was excellent value (ICC = 0.85). The CSI-J was significantly correlated with EQ-5D (r = −0.44), pain intensity (r = 0.42), and pain interference (r = 0.48) (p < 0.01 for all). Ten percent of the participants were above the cutoff “40”. The exploratory factor analysis resulted in 5-factor model.

Conclusions

This study reported that the CSI-J was a useful and psychometrically sound tool to assess CSS in Japanese patients with musculoskeletal disorders. The finding of the prevalence rates of CS severity levels in patients with musculoskeletal disorders may help clinicians to decide strategy of treatment.

Posttraumatic stress disorder influences the nociceptive and intrathecal cytokine response to a painful stimulus in combat veterans

OBJECTIVE

Although posttraumatic stress disorder (PTSD) and chronic pain frequently occur in tandem, the pathophysiological mechanisms mediating this comorbidity are poorly understood. Because excessive inflammation occurs in both conditions, we examined the cerebrospinal fluid (CSF) concentrations of inflammatory response mediators interleukin 1-beta (IL-1β), interleukin 6 (IL-6), interleukin 8 (IL-8), tumor necrosis factor-alpha (TNFα) and interleukin 10 (IL-10) after prolonged suprathreshold pain stimulus in 21 male combat veterans; 10 with PTSD and 11 combat controls (CC).

METHODS

After completing baseline quantitative sensory testing (QST) and psychological profiling, all patients received an injection of capsaicin into the quadriceps muscle. Spontaneously reported pain was measured for 30min after the capsaicin injection. The evoked pain measure of temporal summation was tested between 70 and 110min post capsaicin injection. Inflammatory (IL-1β, IL-6, IL-8 TNFα) and anti-inflammatory (IL-10) CSF cytokines were measured before (baseline) and after capsaicin injection over a time frame of 110min.

RESULTS

Following intramuscular capsaicin injection, pro-inflammatory cytokines [TNFα, IL-6, IL-8] significantly increased (percent rise from baseline) in both groups, whereas IL-1β significantly increased in the PTSD group only. The anti-inflammatory cytokine IL-10 showed an immediate (within 10min) increase in the CC group; however, the IL-10 increase in the PTSD group was delayed and not consistently elevated until 70min post injection.

CONCLUSION

These findings show significant central nervous system (CNS) differences in the inflammatory response to a deep pain stimulus in combat veterans with and without PTSD. They support the concept that abnormally elevated neuroinflammatory response to pain stimuli may be one CNS mechanism accounting for the high co-occurrence of PTSD and pain.

Heightened Temporal Summation of Pain in Patients with Functional Gastrointestinal Disorders and History of Trauma

BACKGROUND

Individuals with functional gastrointestinal disorders (FGIDs) report experiencing trauma more often than healthy controls, but little is known regarding psychophysical correlates.

PURPOSE

The purpose of this study was to test the hypothesis that adolescents and young adults with FGIDs since childhood and a trauma history (n = 38) would exhibit heightened temporal summation to thermal pain stimuli, an index of central sensitization, and greater clinical symptoms compared to patients with FGIDs and no trauma history (n = 95) and healthy controls (n = 135).

METHODS

Participants completed self-report measures, an experimental pain protocol, and psychiatric diagnostic interview as part of a larger longitudinal study.

RESULTS

FGID + Trauma patients exhibited greater temporal summation than FGID + No Trauma patients and healthy controls. Additionally, FGID + Trauma patients exhibited greater gastrointestinal and non-gastrointestinal symptom severity, number of chronic pain sites, and disability.

CONCLUSIONS

Assessing for trauma history in patients with FGIDs could identify a subset at risk for greater central sensitization and pain-related symptoms.

Pain is prevalent among adolescents and equally related to stress across genders

Background

Young people seem increasingly disabled due to pain and stress. Pain and stress are health risks with adverse long-term health effects. Traditionally, these health risks have been most prevalent and strongest associated in females, also regarding children and adolescents. Main objectives in this study were to investigate current gender differences in musculoskeletal pain and perceived stress in adolescents aged 15 and 16 years with respect to prevalence and group differences for various aspects of stress and pain, and to explore the relationship between stress and pain, specified for gender.

Methods

A cross-sectional study was conducted with 17 participating public schools. The survey was administrated by the schools in accordance with given procedures, emphasizing the volunteer and anonymous participation of the pupils. Primary study measurements were pain and stress. The pain measurements addressed different aspects of musculoskeletal pain including pain sites, pain duration and pain intensity (measured by a Visual analogue scale; VAS). The stress instrument used was the Perceived stress questionnaire (PSQ) comprising different factors of stress, i.e. worries, tension, joy and demands. The secondary study measurement was body mass index (BMI).

Results

The study sample comprised 422 adolescents aged 15 and 16 years; 218 females and 204 males. The pain reporting was high in both genders, 57.3 per cent of the females and 44.6 per cent of the males. In general, the female adolescents reported more pain and stress, although several pain measures corresponded between genders. The pain prevalence was similar across genders with respect to lower extremity pain, back pain and arm pain. Lower extremity pain was the most frequent reported pain in both genders. More females reported head pain (Pearson Chi-Square 7.11, p = .008), severe pain (VAS ≥ 7, Pearson Chi-Square 13.12, p = .004) and moderate to severe stress (PSQ ≥ 0.45, Pearson Chi-Square 29.11, p < .001). Comparison analyses of the continuous pain and stress variables revealed significant mean (95% confidence interval [CI]) differences between genders for all stress variables with the highest mean scores in females. In both genders there were significant (p < .01) correlations between all the continuous pain and stress variables. In 9 out of 15 correlations, the stress-pain associations were strongest in males (Pearson product-moment correlation (r) between 0.34 and 0.38). Only in females, the body mass index (BMI) appeared associated (weakly) to pain and stress, in terms of pain intensity (VAS, r = 0.19) and lack of joy (as a factor of stress, r = 0.16).

Conclusion

Pain and stress were prevalent in the adolescent sample, with generally higher reporting among females. Several pain measures corresponded between genders, but stress differed significantly between genders for all variables. Scrutinizing the relationship between pain and stress revealed significant stress-pain associations regarding all variables across genders, i.e. the pain complaints among the adolescents seemed equally related to stress in males and females in the sample.

Perceived stress and musculoskeletal pain are prevalent and significantly associated in adolescents: an epidemiological cross-sectional study

Background

Long-term musculoskeletal pain and negative stress are health risks with adverse long-term health effects, and these health risks seem to increase among young people. The mechanisms behind this are unclear. There is a need for a better understanding of perceived stress and musculoskeletal pain among adolescents, in order to improve health promotion and treatment approaches in this group.

Methods

Objectives were to evaluate the current prevalence of perceived stress and musculoskeletal pain in 15 and 16 year olds, to explore stress-pain associations and the probability that perceived stress (PSQ) was related to the reporting of pain and variations in pain, and to investigate possible differences in stress between different types of musculoskeletal pain in the adolescents. A cross-sectional study was conducted. Elementary schools participated. The outcomes were stress (Perceived stress questionnaire; PSQ) and musculoskeletal pain (pain/no pain, pain sites, pain duration and pain intensity (Visual analogue scale; VAS).

Results

Fifty-one point two percent (N = 422) reported pain, of which 70.8 % reported long-term pain. Some more girls (57.9 %) reported pain. 22.0 % of the study population reported moderate to severe stress (PSQ ≥ 0.45), of which 79.6 % were bothered by pain (Pearson Chi-square 38.47, p ≤ .001). All stress and pain variables were significantly associated (p < .01). The strongest association appeared between pain intensity (VAS) and stress (PSQ) (r = 0.40). Perceived stress (PSQ) was associated with the reporting of pain among the adolescents (Odds Ratio [OR] 1.68) and could explain some of the variation in pain intensity (VAS; β = 0.15, p < .001) and number of pain sites (β = 0.14, p < .01), according to the regression analyses. There were no mean differences in stress (PSQ) between different types of musculoskeletal pain.

Conclusions

There was high prevalence of musculoskeletal pain, long-term pain and moderate to severe stress (PSQ ≥ 0.45) in this study sample. Perceived stress (PSQ) was related to the reporting of musculoskeletal pain among the adolescents and could explain some of the variation in pain intensity (VAS) and number of pain sites. There were no differences in stress levels (PSQ) between different types of musculoskeletal pain in the adolescents.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-015-2414-x) contains supplementary material, which is available to authorized users.

Paradoxical Pain Perception in Posttraumatic Stress Disorder: The Unique Role of Anxiety and Dissociation

Posttraumatic stress disorder (PTSD) and chronic pain often co-occur and exacerbate each other. Elucidating the mechanism of this co-occurrence therefore has clinical importance. Previously, patients with PTSD with chronic pain were found to demonstrate a unique paradoxical pain profile: hyperresponsiveness together with hyposensitivity to pain. Our aim was to examine whether 2 seemingly paradoxical facets of PTSD (anxiety and dissociation) underlie this paradoxical profile. Patients with PTSD (n = 32) and healthy control individuals (n = 43) underwent psychophysical testing and completed questionnaires. Patients with PTSD had higher pain thresholds and higher pain ratings to suprathreshold stimuli than control individuals. Pain thresholds were positively associated with dissociation levels and negatively associated with anxiety sensitivity levels. Experimental pain ratings were positively associated with anxiety sensitivity and negatively related to dissociation levels. Chronic pain intensity was associated with anxiety, anxiety sensitivity, and pain catastrophizing. It appears that reduced conscious attention toward incoming stimuli, resulting from dissociation, causes delayed response in pain threshold measurement, whereas biases toward threatening stimuli and decreased inhibition, possibly caused by increased anxiety, are responsible for the intensification of experimental and chronic pain. The paradoxical facets of PTSD and their particular influences over pain perception seem to reinforce the coexistence of PTSD and chronic pain, and should be considered when treating traumatized individuals.

PERSPECTIVE

This article provides new information regarding the underlying mechanism of the coexistence of PTSD and chronic pain. This knowledge could help to provide better management of PTSD and chronic pain among individuals in the aftermath of trauma.