Sex differences in visceral sensitivity and brain activity in a rat model of comorbid pain: a longitudinal study

ABSTRACT

Temporomandibular disorder (TMD) and irritable bowel syndrome (IBS) are 2 chronic overlapping pain conditions (COPCs) that present with significant comorbidity. Both conditions are more prevalent in women and are exacerbated by stress. While peripheral mechanisms might contribute to pain hypersensitivity for each individual condition, mechanisms underlying the comorbidity are poorly understood, complicating pain management when multiple conditions are involved. In this study, longitudinal behavioral and functional MRI-based brain changes have been identified in an animal model of TMD-like pain (masseter muscle inflammation followed by stress) that induces de novo IBS-like comorbid visceral pain hypersensitivity in rats. In particular, data indicate that increased activity in the insula and regions of the reward and limbic systems are associated with more pronounced and longer-lasting visceral pain behaviors in female rats, while the faster pain resolution in male rats may be due to increased activity in descending pain inhibitory pathways. These findings suggest the critical role of brain mechanisms in chronic pain conditions and that sex may be a risk factor of developing COPCs.

Case report: Remission of chronic low back pain and oral dysesthesia comorbid with attention deficit/hyperactivity disorder by treatment with atomoxetine and pramipexole

Introduction

Oral dysesthesia is a disease characterized by pain and/or abnormal sensations in the oral region, without any organic abnormality. Its symptoms include pain, and it is considered to be a disorder associated with idiopathic oral-facial pain. It is also known that idiopathic oral-facial pain tends to coexist with chronic musculoskeletal pain, including low back pain, even before its onset. Such coexisting idiopathic pain conditions are also called chronic overlapping pain conditions (COPCs). In general, COPCs are often refractory to treatment. Recently, it has been reported that attention deficit hyperactivity disorder (ADHD) is associated with many COPCs, such as pain in the facial and lower back regions and so on. However, there are no reports of (1) ADHD as a comorbidity with oral dysesthesia (OD) or (2) of the therapeutic effects of ADHD medications or dopamine agonists on low back pain and OD or an (3) evaluation of cerebral blood flow over time after treatment with these medications for OD and low back pain.

Case Presentation

In this study, we report the case of an 80-year-old man with OD and chronic low back pain that persisted for more than 25 years. His OD and chronic back pain were refractory to standard treatment, prevented him from continuing work, and tended to be exacerbated by conflicts in his relationship with his son. In recent years, ADHD has often been found to be comorbid with chronic pain, and ADHD medications have been reported to improve chronic pain as well. The patient was confirmed to have undiagnosed ADHD and was treated with the ADHD medication atomoxetine and dopamine agonist pramipexole, which dramatically improved his OD, chronic back pain, and cognitive function. Furthermore, along the course of treatment, there was improvement in cerebral blood flow in his prefrontal cortex, which was thought to reflect improved function in the region. Consequently, he was able to resume work and improve his family relationships.

Conclusion

Therefore, in the cases of ODs and COPCs, screening for ADHD and, if ADHD is diagnosed, ADHD medications or dopamine agonists may be considered.

Chronic overlapping pain conditions and long-term opioid treatment

OBJECTIVES

One in 5 people in the United States lives with chronic pain. Many patients with chronic pain experience a subset of specific co-occurring pain conditions that may share a common pain mechanism and that have been designated as chronic overlapping pain conditions (COPCs). Little is known about chronic opioid prescribing patterns among patients with COPCs in primary care settings, especially among socioeconomically vulnerable patients. This study aims to evaluate opioid prescribing among patients with COPCs in US community health centers and to identify individual COPCs and their combinations that are associated with long-term opioid treatment (LOT).

STUDY DESIGN

Retrospective cohort study.

METHODS

We conducted analyses of more than 1 million patients 18 years and older based on electronic health record data from 449 US community health centers across 17 states between January 1, 2009, and December 31, 2018. Logistic regression models were used to assess the relationship between COPCs and LOT.

RESULTS

Individuals with COPCs were prescribed LOT 4 times more often than individuals without a COPC (16.9% vs 4.0%). The presence of chronic low back pain, migraine headache, fibromyalgia, or irritable bowel syndrome combined with any of the other COPCs increased the odds of LOT prescribing compared with the presence of a single COPC.

CONCLUSIONS

Although LOT prescribing has declined over time, it remains relatively high among patients with certain COPCs and for those with multiple COPCs. These study findings suggest target populations for future interventions to manage chronic pain among socioeconomically vulnerable patients.

Circulating Polyunsaturated Fatty Acids and Pain Intensity in Five Chronic Pain Conditions

Pain intensity is well-known to be influenced by a wide range of biobehavioral variables. Nutritional factors, however, have not been generally considered for their potential importance. This cross-sectional study examined associations between erythrocyte omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFAs) and pain intensity in 605 adults. Pain intensity was computed on a 0 to 100 numeric rating scale from questions about 5 chronic pain conditions: orofacial pain, headache, low back pain, irritable bowel syndrome, and bodily pain. For each pain condition, multiple linear regression tested the hypothesis that a higher ratio of n-6 arachidonic acid to the sum of n-3 eicosapentaenoic acid and docosahexaenoic acid (AA/(EPA+DHA) was associated with greater pain intensity. In covariate-adjusted analysis, orofacial pain intensity increased 5.7 points (95% CI: 1.4, 9.9) per unit increase in n-6/n-3 PUFA ratio. Likewise, a 1 unit increase in n-6/n-3 PUFA ratio was associated with significant increases in pain intensity (range 5-8 points) of headache pain, low back pain, and bodily pain, but not abdominal pain. Separate multiple linear regression models investigated the independent strength of association of individual PUFAs to the intensity of each pain condition. Overall, n-3 docosahexaenoic acid was most strongly, and inversely, associated with pain intensity. PERSPECTIVE: A higher ratio of n-6/n-3 long-chain polyunsaturated fatty acids was associated greater pain intensity for orofacial pain, headache, low back pain, and bodily pain, but not abdominal pain. The n-6/n-3 PUFA ratio was more consistently associated with pain intensity than any individual constituent of the long-chain PUFA ratio.

How negative and positive constructs and comorbid conditions contribute to disability in chronic orofacial pain

BACKGROUND

Temporomandibular disorders (TMD) symptoms develop into chronic pain for some patients, but the reasons for this are unclear. Psychosocial factors and chronic overlapping pain conditions are believed to contribute to the development of pain-related disability. We examined the role of jaw function, negative and positive psychological factors and chronic overlapping pain conditions (COPCs) on pain-related disability whilst controlling for demographic variables.

METHODS

We collected demographics, medical and psychosocial history and the Graded Chronic Pain Scale, a measure of pain intensity and pain interference from 400 participants with chronic TMD. Structural equation modelling was used to assess a model of COPCs and the latent variables of psychological unease (pain catastrophizing, somatic symptoms and negative affect), positive valence factors (optimism and positive affect), jaw function (chewing, opening and expression limitation) and pain-related disability (pain intensity and pain interference) whilst controlling for demographic variables.

RESULTS

We achieved good fit of a parsimonious model (root-mean-square error of approximation = 0.063 [90% CI] [0.051-0.075]), comparative fit index = 0.942, standard root-mean-square residual = 0.067. Jaw function was the strongest latent variable predictor, followed by psychological unease and COPCs suggesting resources focused on improving joint function, psychosocial support and management of COPCs will improve pain-related disability in TMDs.

CONCLUSIONS

These findings not only increase the body of knowledge related to TMD clinical phenotypes but also, have a translational impact in further supporting the potential value of targeting physical therapy such as jaw exercise along with psychological interventions as multidisciplinary nonpharmacological therapeutic solutions.

Rationale and design of a multicenter randomized clinical trial of vestibulodynia: understanding pathophysiology and determining appropriate treatments (vestibulodynia: UPDATe)

BACKGROUND

Limited data are available to establish evidence-based management protocols for vestibulodynia (VBD), a chronic vulvar pain condition that affects approximately 14 million women in the U.S. For the purposes of the study, our group subdivided VBD subtypes that may benefit from different types of treatment: 1) VBD peripheral (VBD-p), characterized by pain localized to the vulvar vestibule and 2) VBD central (VBD-c), characterized by VBD alongside one or more other chronic overlapping pain conditions (e.g. irritable bowel syndrome, temporomandibular disorder, and fibromyalgia syndrome) that affect remote body regions. Here, we describe the rationale and design of an NIH-funded multicenter clinical trial comparing the effectiveness of topical and/or systemic medication for alleviating pain and normalizing pain- relevant biomarkers among women with VBD-p and VBD-c.

METHODS

Participants will be randomly assigned to one of four parallel arms: peripheral treatment with 5% lidocaine + 0.5 mg/ml 0.02% oestradiol compound cream + oral placebo pill, 2) central treatment with the tricyclic antidepressant nortriptyline + placebo cream, 3) combined peripheral cream and central pill treatments, or 4) placebo cream and placebo pill. The treatment phase will last 16 weeks, with outcome measures and biomarkers assessed at 4 time points (0, 8, 16, and 24 weeks). First, we will compare the efficacy of treatments in alleviating pain using standardized tampon insertion with a numeric rating scale and self-reported pain on the short form McGill Pain Questionnaire. Next, we will compare the efficacy of treatments in improving perceived physical, mental, and sexual health using standardized questionnaires. Finally, we will measure cytokines and microRNAs in local vaginal and circulating blood samples using multiplex assays and RNA sequencing, and determine the ability of these biomarkers to predict treatment response.

CONCLUSION

This is the first multicenter randomized controlled trial to evaluate the efficacy of peripherally and centrally acting medications currently used in clinical practice for treating unique VBD subtypes based on distinct clinical and biological signatures.

ADMINISTRATIVE INFORMATION

Vestibulodynia UPDATe is a multi-centre, two-by-two factorial designed randomized, double-blind, placebo-controlled trial registered at clinical trials.gov (NCT03844412). This work is supported by the R01 HD096331 awarded to Drs. Nackley, Rapkin, Geller and Carey by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).Key messagesPeripheral lidocaine and oestradiol and centrally-targeted nortriptyline medications are used for the treatment of pain in women with VBD, but there is a lack of data from well-powered RCTs.This two-by-two factorial RCT will test the efficacy of these medications in VBD subtypes characterized by distinct clinical characteristics and biomarker profiles.We hope that results will provide clinicians with scientific evidence of therapeutic efficacy in distinct VBD subtypes in an effort to direct and optimize treatment approaches.

Migraine in the context of chronic primary pain, chronic overlapping pain disorders, and functional somatic disorders: A narrative review

OBJECTIVE

To contextualize migraine as the most common primary headache disorder in relation to other chronic primary pain and non-pain functional somatic and mental conditions.

BACKGROUND

Migraine is increasingly understood as a sensory processing disorder within a broader spectrum of symptom disorders. This has implications for diagnosis and treatment.

METHOD

Narrative review based on a search of the literature of the last 15 years on the overlap of migraine with other symptom disorders.

RESULTS

Migraine as the prototypical primary headache disorder not only comprises many non-headache symptoms in itself, it also shows high comorbidity with other chronic pain and non-pain conditions (e.g., fibromyalgia syndrome, irritable bowel syndrome, functional non-epileptic seizures, depression, anxiety, and posttraumatic stress disorder). Such "symptom disorders" share several etiological factors (e.g., female preponderance, psychological vulnerability) and psychophysiological mechanisms (e.g., altered sensory processing, pain expectancy). These facts are acknowledged by several recent integrative conceptualizations such as chronic primary pain, chronic overlapping pain conditions, or functional somatic disorders. Accordingly, migraine management increasingly addresses the total symptom burden and individual contributors to symptom experience, and thus incorporates centrally acting pharmacological and non-pharmacological, that is, psychological and behavioral, treatment approaches.

CONCLUSIONS

Migraine and also other primary headache disorders should be seen as particular phenotypes within a broader spectrum of symptom perception and processing disorders that require integrative diagnostics and treatment. A harmonization of classifications and better interdisciplinary collaboration are desirable.

Genome-wide analysis identifies impaired axonogenesis in chronic overlapping pain conditions

Chronic pain is often present at more than one anatomical location, leading to chronic overlapping pain conditions (COPC). Whether COPC represents a distinct pathophysiology from the occurrence of pain at only one site is unknown. Using genome-wide approaches, we compared genetic determinants of chronic single-site vs. multisite pain in the UK Biobank. We found that different genetic signals underlie chronic single-site and multisite pain with much stronger genetic contributions for the latter. Among 23 loci associated with multisite pain, 9 loci replicated in the HUNT cohort, with the DCC netrin-1 receptor (DCC) as the top gene. Functional genomics identified axonogenesis in brain tissues as the major contributing pathway to chronic multisite pain. Finally, multimodal structural brain imaging analysis showed that DCC is most strongly expressed in subcortical limbic regions and is associated with alterations in the uncinate fasciculus microstructure, suggesting that DCC-dependent axonogenesis may contribute to COPC via cortico-limbic circuits.

Examining the Adjustment Patterns of Adults With Multiple Chronic Pain Conditions and Multiple Pain Sites: More Pain, No Gain

The present study examined how multiple chronic pain conditions and pain sites are associated with sociodemographics, chronic pain adjustment profiles, and emotional distress. A total of 2,407 individuals who reported at least 6 months of having consistent pain severity, pain interference, and/or emotional burden due to pain were recruited through random digit dialing across the United States. Participants' chronic pain adjustment profiles (ie, pain intensity, pain interference, emotional burden, pain catastrophizing, pain coping, pain attitudes, and social resources) were assessed. Anxiety and depressive symptoms were also measured using a subsample of 181 participants who provided 3-month follow-up data. More than 60% of individuals with chronic pain reported having multiple pain conditions. Middle-aged single women with fibromyalgia, disability and of low socioeconomic status reported a greater number of pain conditions and pain sites. Structural equation modeling revealed that a higher number of pain conditions and sites were associated with more dysfunctional chronic pain adjustment profiles. The subsample analyses showed that reporting a greater number of pain conditions predicted a higher level of depression and anxiety 3 months later, controlling for pain-related anxiety and depressive symptoms, pain severity and interference at baseline. Having multiple pain conditions and sites may represent a psychosocial barrier to successful adjustment to chronic pain. PERSPECTIVE: This article argues for the importance of assessing the number of co-occurring chronic pain conditions and bodily areas that are affected by pain in both pain research and clinical settings. Measuring and incorporating such information could potentially enhance our nascent understanding of the adjustment processes of chronic pain.

How can precision medicine be applied to temporomandibular disorders and its comorbidities?

The Eighth Scientific Meeting of The TMJ Association, Ltd. was held in Bethesda, Maryland, September 11-13, 2016. As in the past, the meeting was cosponsored by components of the National Institutes of Health with speakers invited to review the state of temporomandibular disorder science and propose recommendations to further progress. The theme of precision medicine, which aims to tailor disease treatment and prevention to match the characteristics of an individual patient (genetic, epigenetic, environmental, lifestyle) underscored the current consensus that temporomandibular disorders are no longer viewed as local conditions of jaw pain and dysfunction. Rather, they represent a complex family of biopsychosocial disorders that can progress to chronic pain, most often accompanied by one or more other chronic pain conditions. Temporomandibular disorders and these comorbidities, called chronic overlapping pain conditions, predominantly or exclusively affect women in their childbearing years and reflect central nervous system sensitization. Presenters at the meeting included leaders in temporomandibular disorder and pain research, temporomandibular disorder patients and advocates, and experts in other fields or in the use of technologies that could facilitate the development of precision medicine approaches in temporomandibular disorders.