Grand Challenges in Musculoskeletal Pain Research: Chronicity, Comorbidity, Immune Regulation, Sex Differences, Diagnosis, and Treatment Opportunities

Elevated circulating soluble interleukin-2 receptor (sCD25) level is associated with prefrontal excitatory-inhibitory imbalance in individuals with chronic pain: A proton MRS study

Aberrant neuronal excitability in the anterior cingulate cortex (ACC) is implicated in cognitive and affective pain processing. Such excitability may be amplified by activated circulating immune cells, including T lymphocytes, that interact with the central nervous system. Here, we conducted a study of individuals with chronic pain using magnetic resonance spectroscopy (MRS) to investigate the clinical evidence for the interaction between peripheral immune activation and prefrontal excitatory-inhibitory imbalance. In thirty individuals with chronic musculoskeletal pain, we assessed markers of peripheral immune activation, including soluble interleukin-2 receptor alpha chain (sCD25) levels, as well as brain metabolites, including Glx (glutamate + glutamine) to GABA+ (γ-aminobutyric acid + macromolecules/homocarnosine) ratio in the ACC. We found that the circulating level of sCD25 was associated with prefrontal Glx/GABA+. Greater prefrontal Glx/GABA+ was associated with higher pain catastrophizing, evaluative pain ratings, and anxiodepressive symptoms. Further, the interaction effect of sCD25 and prefrontal Glx/GABA+ on pain catastrophizing was significant, indicating the joint association of these two markers with pain catastrophizing. Our results provide the first evidence suggesting that peripheral T cellular activation, as reflected by elevated circulating sCD25 levels, may be linked to prefrontal excitatory-inhibitory imbalance in individuals with chronic pain. The interaction between these two systems may play a role as a potential mechanism underlying pain catastrophizing. Further prospective and treatment studies are needed to elucidate the specific role of the immune and brain interaction in pain catastrophizing.

Pain-sensorimotor interactions: New perspectives and a new model

How pain and sensorimotor behavior interact has been the subject of research and debate for many decades. This article reviews theories bearing on pain-sensorimotor interactions and considers their strengths and limitations in the light of findings from experimental and clinical studies of pain-sensorimotor interactions in the spinal and craniofacial sensorimotor systems. A strength of recent theories is that they have incorporated concepts and features missing from earlier theories to account for the role of the sensory-discriminative, motivational-affective, and cognitive-evaluative dimensions of pain in pain-sensorimotor interactions. Findings acquired since the formulation of these recent theories indicate that additional features need to be considered to provide a more comprehensive conceptualization of pain-sensorimotor interactions. These features include biopsychosocial influences that range from biological factors such as genetics and epigenetics to psychological factors and social factors encompassing environmental and cultural influences. Also needing consideration is a mechanistic framework that includes other biological factors reflecting nociceptive processes and glioplastic and neuroplastic changes in sensorimotor and related brain and spinal cord circuits in acute or chronic pain conditions. The literature reviewed and the limitations of previous theories bearing on pain-sensorimotor interactions have led us to provide new perspectives on these interactions, and this has prompted our development of a new concept, the Theory of Pain-Sensorimotor Interactions (TOPSMI) that we suggest gives a more comprehensive framework to consider the interactions and their complexity. This theory states that pain is associated with plastic changes in the central nervous system (CNS) that lead to an activation pattern of motor units that contributes to the individual's adaptive sensorimotor behavior. This activation pattern takes account of the biological, psychological, and social influences on the musculoskeletal tissues involved in sensorimotor behavior and on the plastic changes and the experience of pain in that individual. The pattern is normally optimized in terms of biomechanical advantage and metabolic cost related to the features of the individual's musculoskeletal tissues and aims to minimize pain and any associated sensorimotor changes, and thereby maintain homeostasis. However, adverse biopsychosocial factors and their interactions may result in plastic CNS changes leading to less optimal, even maladaptive, sensorimotor changes producing motor unit activation patterns associated with the development of further pain. This more comprehensive theory points towards customized treatment strategies, in line with the management approaches to pain proposed in the biopsychosocial model of pain.

The influence of pain-related comorbidities on pain intensity and pain-related psychological distress in patients presenting with musculoskeletal pain

BACKGROUND

Musculoskeletal pain (MSP) is the largest contributor to chronic pain and frequently occurs alongside other medical comorbidities.

OBJECTIVE

Explore the relationships between the presence of pain-related comorbidities, pain intensity, and pain-related psychological distress in patients with MSP.

METHODS

A longitudinal assessment of individuals 18-90 years old in the Midwestern United States beginning a new episode of physical therapy for MSP. Electronic medical records were assessed the full year prior for care-seeking of diagnoses for pain-related comorbidities (anxiety, metabolic disorder, chronic pain, depression, nicotine dependence, post-traumatic stress disorder, sleep apnea, and sleep insomnia). Pain intensity and pain-related psychological distress (Optimal Screening for Prediction of Referral and Outcome - Yellow Flags tool) were captured during the physical therapy evaluation. Generalized linear models were used to assess the association between pain intensity, psychological distress, and pain-related co-morbidities. Models were adjusted for variables shown in the literature to influence pain.

RESULTS

532 participants were included in the cohort (56.4% female; median age of 59 years, Interquartile Range [IQR]:47, 69). Comorbid depression (beta coefficient (β) = 0.7; 95%CI: 0.2, 1.2), spine versus lower extremity pain ((β = 0.6; 95%CI: 0.1, 1.1), and prior surgery (β = 0.8, 95%CI: 0.3, 1.4) were associated with higher pain intensity scores. No pain-related comorbidities were associated with pain-related psychological distress (yellow flag count or number of domains). Female sex was associated with less pain-related psychological distress (β = -0.2, 95%CI: -0.3, -0.02).

CONCLUSIONS

Depression was associated with greater pain intensity. No comorbidities were able to account for the extent of pain-related psychological distress.

A mixed-methods feasibility study of a comorbidity-adapted exercise program for low back pain in older adults (COMEBACK): a protocol

BACKGROUND

The prevalence of low back pain increases with age and has a profound impact on physical and psychosocial health. With increasing age comes increasing comorbidity, and this also has pronounced health consequences. Whilst exercise is beneficial for a range of health conditions, trials of exercise for low back pain management often exclude older adults. It is currently unknown whether an exercise program for older adults with low back pain, tailored for the presence of comorbidities, is acceptable for participants and primary healthcare providers (PHCPs). Therefore, this mixed-methods study will assess the feasibility of an 8-week comorbidity-adapted exercise program for older people with low back pain and comorbid conditions.

METHODS

The 3-phased feasibility study will be performed in a primary healthcare setting. PHCPs will be trained to deliver a comorbidity-adapted exercise program for older people with low back pain and comorbidities. Healthcare-seeking adults > 65 will be screened for eligibility over telephone, with a recruitment target of 24 participants. Eligible participants will attend an initial appointment (diagnostic phase). During this initial appointment, a research assistant will collect patient demographics, self-reported outcome measurement data, and perform a physical and functional examination to determine contraindications and restrictions to an exercise program. During the development phase, PHCPs will adapt the exercise program to the individual and provide patient education. During the intervention phase, there will be two supervised exercise sessions per week, over 8 weeks (total of 16 exercise sessions). Each exercise session will be approximately 60 min in duration. A qualitative evaluation after the last exercise program session will explore the feasibility of the exercise program for participants and PHCPs. Progression criteria will determine the suitability for a fully powered randomised controlled trial.

DISCUSSION

This mixed-methods feasibility study will assess an exercise program for older adults with low back pain and comorbidities. Once assessed for feasibility, the exercise program may be tested for effectiveness in a larger, fully powered randomised controlled trial. This information will add to the sparse evidence base on appropriate options for managing back pain in older adults.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry registration number: ACTRN12621000379819p (06/04/2021; https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?ACTRN=12621000379819p ).

TRIAL SPONSOR

Macquarie University, Department of Chiropractic, Faculty of Medicine, Health and Human Sciences, Macquarie University, NSW 2109, Australia.