Pathological mechanism of musculoskeletal manifestations associated with CRPS type II: an animal study

Intramuscular botulinum toxin-A in complex regional pain syndrome resistant to standard treatment: a case report

OBJECTIVE

To present a patient with complex regional pain syndrome type 1 (CRPS-I) and improvement of contracture of hand muscles and grip strength after successful treatment with botulinum neurotoxin‑A (BoNT-A).

CASE

A 53-year-old woman with CRPS‑I experienced severe allodynia, swelling and autonomic changes in the left hand after a distal radius fracture. Over the succeeding months, she developed contracture of the left hand muscles which was treated with injection of BoNT‑A into the hand muscles (10 points).

RESULTS

In the patient treatment with BoNT‑A an improvement was seen in the hand range of motion (ROM) and grip strength.

CONCLUSION

Successful results can be obtained with BoNT‑A injection in treatment-resistant CRPS‑I cases which may develop joint contracture.

The Role of Neuroinflammation in Complex Regional Pain Syndrome: A Comprehensive Review

Complex Regional Pain Syndrome (CRPS) is an excess and/or prolonged pain and inflammation condition that follows an injury to a limb. The pathogenesis of CRPS is multifaceted that remains incompletely understood. Neuroinflammation is an inflammatory response in the peripheral and central nervous systems. Dysregulated neuroinflammation plays a crucial role in the initiation and maintenance of pain and nociceptive neuronal sensitization, which may contribute to the transition from acute to chronic pain and the perpetuation of chronic pain in CRPS. The key features of neuroinflammation encompass infiltration and activation of inflammatory cells and the production of inflammatory mediators in both the central and peripheral nervous systems. This article reviews the role of neuroinflammation in the onset and progression of CRPS from six perspectives: neurogenic inflammation, neuropeptides, glial cells, immune cells, cytokines, and keratinocytes. The objective is to provide insights that can inform future research and development of therapeutic targets for CRPS.

Perineural treatment with anti-TNF-α antibody ameliorates persistent allodynia and edema in novel mouse models with complex regional pain syndrome

Complex regional pain syndrome (CRPS) is an intractable chronic pain syndrome with various signs and symptoms including allodynia/hyperalgesia, edema, swelling, and skin abnormalities. However, a definitive therapeutic treatment for CRPS has not been established. In CRPS patients, inflammatory cytokines such as TNF-α and IL-1β have been shown to increase in affected areas, suggesting that these molecules may be potential therapeutic targets for CRPS. Here, we first created a novel CRPS mouse model (CRPS-II-like) via sciatic nerve injury and cast immobilization, which was characterized by mechanical allodynia, local edema, and skin abnormalities, to evaluate the pathophysiology and pharmacotherapy of CRPS. When an anti-TNF-α antibody was consecutively administered near the injured sciatic nerve of CRPS model mice, persistent allodynia and CRPS-related signs in the ipsilateral hindpaw were markedly attenuated to control levels. Perineural administration of anti-TNF-α antibody also suppressed the upregulation of inflammatory cytokines as well as the activation of macrophages and Schwann cells in the injured sciatic nerve. These findings indicate that persistent allodynia and CRPS-related signs in CRPS models are primarily associated with TNF-α-mediated immune responses in injured peripheral nerves, suggesting that perineural treatment with anti-TNF-α antibody might be therapeutically useful.

Animal models of complex regional pain syndrome: A scoping review

BACKGROUND

complex regional pain syndrome (CRPS) leads to a debilitating chronic pain condition. The lack of cause, etiology, and treatment for CRPS has been widely explored in animal models.

OBJECTIVE

Provide a comprehensive framework of the animal models used for investigating CRPS.

ELIGIBILITY CRITERIA

Preclinical studies to induce the characteristics of CRPS, with a control group, in any language or publication date.

SOURCES OF EVIDENCE

The search was performed in the Medline (PubMed) and ScienceDirect databases.

RESULTS

93 studies are included. The main objective of the included studies was to understand the CRPS model. Rats, males and adults, exposed to ischemia/reperfusion of the paw or fracture of the tibia were the most common characteristics. Nociceptive evaluation using von Frey monofilaments was the most widely adopted in the studies.

CONCLUSIONS

For the best translational science between the animal models and individuals with CRPS, future studies should include more heterogeneous animals, and multiple assessment tools, in addition to improving the description and performance of measures that reduce the risk of bias.

Myofascial Pain as an Unseen Comorbidity in Osteoarthritis: A Scoping Review

OBJECTIVE

This review aimed to identify, summarize, and appraise the evidence supporting the coexistence of myofascial pain (MPS) and trigger points (MTrP) in osteoarthritis (OA), and the effectiveness of MTrPs treatments in OA-related pain and physical function outcomes.

METHODS

Three databases were searched from inception to June 2022. We included observational and experimental studies to fulfill our 2 study aims. Two independent reviewers conducted 2-phase screening procedures and risk of bias using checklist tools for cross-sectional, quasi-experimental, and randomized control trials. Patient characteristics, findings of active and latent MTrPs in relevant muscles, treatments, and pain and physical function outcomes were extracted from low-risk bias studies.

RESULTS

The literature search yielded 2898 articles, of which 6 observational and 7 experimental studies had a low bias risk and the data extracted. Active MTrPs in knee OA patients was more evident in the quadriceps and hamstring muscles than in healthy individuals. Dry needling on active MTrPs improved pain and physical function in the short term compared with sham treatment in hip OA patients. In knee OA, dry needling on latent or active MTrPs improved pain and functional outcomes compared with sham needling but did not result in better pain and physical outcomes when combined with a physical exercise program.

DISCUSSION

The presence of active versus latent MTrPs seems to be a more sensitive discriminating feature of OA given that latent is often present in OA and healthy individuals. Dry needling on active MTrPs improved pain and physical function in the short term compared with sham treatment in hip OA patients. However, the small sample size and the few number of studies limit any firm recommendation on the treatment.

REGISTRY

The study protocol was prospectively registered in Open Science Framework (https://doi.org/10.17605/OSF.IO/8DVU3).

Muscle contractile exercise through a belt electrode device prevents myofiber atrophy, muscle contracture, and muscular pain in immobilized rat gastrocnemius muscle

Purpose

Immobilization of skeletal muscles causes muscle atrophy, muscle contracture, and muscle pain, the mechanisms of which are related to macrophage accumulation. However, muscle contractile exercise through a belt electrode device may mitigate macrophage accumulation. We hypothesized that such exercise would be effective in preventing myofiber atrophy, muscle contracture, and muscular pain. This study tested this hypothesis in immobilized rat gastrocnemius muscle.

Materials and methods

A total of 32 rats were divided into the following control and experimental groups: immobilization (immobilized treatment only), low-frequency (LF; immobilized treatment and muscle contractile exercise with a 2 s (do) /6 s (rest) duty cycle), and high-frequency (HF; immobilized treatment and muscle contractile exercise with a 2 s (do)/2 s (rest) duty cycle). Electrical stimulation was performed at 50 Hz and 4.7 mA, and muscle contractile exercise was applied to the lower limb muscles for 15 or 20 min/session (once daily) for 2 weeks (6 times/week). After the behavioral tests, the bilateral gastrocnemius muscles were collected for analysis.

Results

The number of macrophages, the Atrogin-1 and MuRF-1 mRNA expression, and the hydroxyproline content in the HF group were lower than those in the immobilization and LF groups. The cross-sectional area (CSA) of type IIb myofibers in the superficial region, the PGC-1α mRNA expression, and the range of motion of dorsiflexion in the HF group were significantly higher than those in the immobilization and LF groups. The pressure pain thresholds in the LF and HF groups were significantly higher than that in the immobilization group, and the nerve growth factor (NGF) content in the LF and HF groups was significantly lower than that in the immobilization group.

Conclusion

Muscle contractile exercise through the belt electrode device may be effective in preventing immobilization-induced myofiber atrophy, muscle contracture, and muscular pain in the immobilized rat gastrocnemius muscle.

Re-Examining Myofascial Pain Syndrome: Toward Biomarker Development and Mechanism-Based Diagnostic Criteria

PURPOSE OF REVIEW

We discuss the need for a mechanism-based diagnostic framework with a focus on the development of objective measures (e.g., biomarkers) that can potentially be added to the diagnostic criteria of the syndrome. Potential biomarkers are discussed in relation to current knowledge on the pathophysiology of myofascial pain syndrome (MPS), including alterations in redox status, inflammation, and the myofascial trigger point (MTrP) biochemical milieu, as well as imaging and neurophysiological outcomes. Finally, we discuss the long-term goal of conducting a Delphi survey, to assess the influence of putative MPS biomarkers on clinician opinion, in order to ultimately develop new criteria for the diagnosis of MPS.

RECENT FINDINGS

Myofascial pain syndrome (MPS) is a prevalent healthcare condition associated with muscle weakness, impaired mood, and reduced quality of life. MPS is characterized by the presence of myofascial trigger points (MTrPs): stiff and discrete nodules located within taut bands of skeletal muscle that are painful upon palpation. However, physical examination of MTrPs often yields inconsistent results, and there is no gold standard by which to diagnose MPS. The current MPS diagnostic paradigm has an inherent subjectivity and the absence of correlation with the underlying pathophysiology. Recent advancements in ultrasound imaging, systemic biomarkers, MTrP-specific biomarkers, and the assessment of dysfunction in the somatosensorial system may all contribute to improved diagnostic effectiveness of MPS.

Does the Interaction between Local and Systemic Inflammation Provide a Link from Psychology and Lifestyle to Tissue Health in Musculoskeletal Conditions?

Musculoskeletal conditions are known to involve biological, psychological, social and, often, lifestyle elements. However, these domains are generally considered in isolation from each other. This siloed approach is unlikely to be adequate to understand the complexity of these conditions and likely explains a major component of the disappointing effects of treatment. This paper presents a hypothesis that aims to provide a foundation to understand the interaction and integration between these domains. We propose a hypothesis that provides a plausible link between psychology and lifestyle factors with tissue level effects (such as connective tissue dysregulation/accumulation) in musculoskeletal conditions that is founded on understanding the molecular basis for interaction between systemic and local inflammation. The hypothesis provides plausible and testable links between mind and body, for which empirical evidence can be found for many aspects. We present this hypothesis from the perspective of connective tissue biology and pathology (fibrosis), the role of inflammation locally (tissue level), and how this inflammation is shaped by systemic inflammation through bidirectional pathways, and various psychological and lifestyle factors via their influence on systemic inflammation. This hypothesis provides a foundation for new consideration of the development and refinement of personalized multidimensional treatments for individuals with musculoskeletal conditions.

Responses of cutaneous C-fiber afferents and spinal microglia after hindlimb cast immobilization in rats

Previous studies have shown that persistent limb immobilization using a cast increases nociceptive behavior to somatic stimuli in rats. However, the peripheral neural mechanisms of nociception remain unclear. Using single-fiber electrophysiological recordings in vitro, we examined the general characteristics of cutaneous C-fiber afferents in the saphenous nerve and their responsiveness to mechanical and heat stimuli in a rat model of immobilization-induced pain by subjecting the rats to hindlimb cast immobilization for 4 weeks. The mechanical response of C-fibers appeared to increase in the model; however, statistical analysis revealed that neither the response threshold nor the response magnitude was altered. The general characteristics and heat responses of the C-fibers were not altered. The number of microglia and cell diameters significantly increased in the superficial dorsal horn of the lumbar spinal cord. Thus, activated microglia-mediated spinal mechanisms are associated with the induction of nociceptive hypersensitivity in rats after persistent cast immobilization.

Experimentally induced spine osteoarthritis in rats leads to neurogenic inflammation within neurosegmentally linked myotomes

Naturally occurring spine osteoarthritis is clinically associated with the manifestation of chronic inflammatory muscle (myofascial) disease. The purpose of this study was to investigate the causal association between experimentally induced spine osteoarthritis and neurogenic inflammatory responses within neurosegmentally linked myotomes. Wistar Kyoto rats were randomly assigned to spine facet compression surgery (L4-L6) or sham surgery. Animals exposed to facet compression surgery demonstrated radiographic signs of facet-osteoarthritis (L4-L6 spinal levels) and sensory changes (allodynia, thermal hyperalgesia) at 7, 14 and 21 days post-intervention, consistent with the induction of central sensitization; no radiologic or sensory changes were observed after sham surgery. Increased levels of proinflammatory biomarkers including substance P (SP), calcitonin gene related peptide (CGRP), protease-activated receptor-2 (PAR2) and calcium/calmodulin dependent protein kinase II (CaMKII) were observed post-surgery within neurosegmentally-linked rectus femoris (L2-L5) muscle when compared to the non-segmentally linked biceps brachii (C4-C7) muscle; no differences were observed between muscles in the sham surgery group. These findings offer novel insight into the potential role of spine osteoarthritis and neurogenic inflammatory mechanisms in the pathophysiology of chronic inflammatory muscle (myofascial) disease.

Mechanisms underlying immobilization-induced muscle pain in rats

INTRODUCTION

We investigated the mechanisms underlying immobilization-induced muscle pain in rats.

METHODS

In rat skeletal muscle, pressure pain threshold (PPT) of the gastrocnemius muscle was measured, and nerve growth factor (NGF) level, peripheral nerve fiber density, macrophage number, and interleukin-1β (IL-1β) mRNA expression were examined. An NGF receptor inhibitor was injected intramuscularly to assess the relationship between PPT and NGF levels.

RESULTS

Immobilization resulted in a decrease in PPT and increases in NGF level, C-fiber density, M1 macrophage number, and IL-1β mRNA expression. Injection of NGF receptor inhibitor reversed the decrease in PPT.

DISCUSSION

NGF upregulation may be a major contributor to immobilization-induced muscle pain. The increases in C-fiber density, M1 macrophage number, and IL-1β mRNA expression may be related to immobilization-induced muscle pain.

The Rodent Tibia Fracture Model: A Critical Review and Comparison With the Complex Regional Pain Syndrome Literature

Distal limb fracture is the most common cause of complex regional pain syndrome (CRPS), thus the rodent tibia fracture model (TFM) was developed to study CRPS pathogenesis. This comprehensive review summarizes the published TFM research and compares these experimental results with the CRPS literature. The TFM generated spontaneous and evoked pain behaviors, inflammatory symptoms (edema, warmth), and trophic changes (skin thickening, osteoporosis) resembling symptoms in early CRPS. Neuropeptides, inflammatory cytokines, and nerve growth factor (NGF) have been linked to pain behaviors, inflammation, and trophic changes in the TFM model and proliferating keratinocytes were identified as the primary source of cutaneous cytokines and NGF. Tibia fracture also activated spinal glia and upregulated spinal neuropeptide, cytokine, and NGF expression, and in the brain it changed dendritic architecture. B cell-expressed immunoglobulin M antibodies also contributed to pain behavior, indicating a role for adaptive immunity. These results modeled many findings in early CRPS, but significant differences were also noted.

PERSPECTIVE

Multiple neuroimmune signaling mechanisms contribute to the pain, inflammation, and trophic changes observed in the injured limb of the rodent TFM. This model replicates many of the symptoms, signs, and pathophysiology of early CRPS, but most post-fracture changes resolve within 5 months and may not contribute to perpetuating chronic CRPS.

Quantification of edematous changes by diffusion magnetic resonance imaging in gastrocnemius muscles after spinal nerve ligation

Patients with complex regional pain syndrome (CRPS) exhibit diverse symptoms, such as neuropathic pain, allodynia, local edema and skin color changes in the affected lesion. Although nerve injury may cause CRPS, pathophysiological mechanisms underlying the syndrome are unclear, and local edema, a characteristic of CRPS, has not been evaluated quantitatively for technical reasons. Here, using a rat spinal nerve ligation-induced CRPS model, we show that edematous changes in gastrocnemius muscle can be detected quantitatively by diffusion magnetic resonance imaging (MRI). Using the line-scan diffusion spectrum on a 1.5 T clinical MR imager, we demonstrate significant elevation of the apparent diffusion coefficient (ADC) ratios in gastrocnemius muscle on the ligated versus the sham-operated rats by one day after surgery, those ratios gradually decreased over time. Meanwhile, T2 ratios in gastrocnemius muscle on the ligated rats increased gradually and significantly, peaking two weeks after surgery, and those ratios remained high and were consistent with edema. Expression of vascular endothelial growth factor (VEGF), a key regulator of blood vessel formation and function, was significantly lower in gastrocnemius muscle on the ligated versus non-ligated side, suggesting that nerve ligation promotes edematous changes and perturbs VEGF expression in target muscle.

Complex regional pain syndrome-significant progress in understanding

Research into complex regional pain syndrome (CRPS) has made significant progress. First, there was the implementation of the official IASP "Budapest" diagnostic criteria. It would be desirable to also define exclusion and outcome criteria that should be reported in studies. The next step was to recognize the complex pathophysiology. After trauma, some inflammation is physiological; in acute CRPS, this inflammation persists for months. There is an abundance of inflammatory and a lack of anti-inflammatory mediators. This proinflammatory network (cytokines and probably also other mediators) sensitizes the peripheral and spinal nociceptive system, it facilitates the release of neuropeptides from nociceptors inducing the visible signs of inflammation, and it stimulates bone cell or fibroblast proliferation, and endothelial dysfunction leading to vascular changes. Trauma may also expose nervous system structures to the immune system and triggers autoantibodies binding to adreno- and acetylcholine receptors. In an individual time frame, the pain in this inflammatory phase pushes the transition into "centralized" CRPS, which is dominated by neuronal plasticity and reorganization. Sensory-motor integration becomes disturbed, leading to a loss of motor function; the body representation is distorted leading to numbness and autonomic disturbances. In an attempt to avoid pain, patients neglect their limb and learn maladaptive nonuse. The final step will be to assess large cohorts and to analyze these data together with data from public resources using a bioinformatics approach. We could then develop diagnostic toolboxes for individual pathophysiology and select focused treatments or develop new ones.

The complex regional pain syndrome

Complex regional pain syndrome (CRPS) is the current consensus-derived name for a syndrome usually triggered by limb trauma. Required elements include prolonged, disproportionate distal-limb pain and microvascular dysregulation (e.g., edema or color changes) or altered sweating. CRPS-II (formerly "causalgia") describes patients with identified nerve injuries. CRPS-I (formerly "reflex sympathetic dystrophy") describes most patients who lack evidence of specific nerve injuries. Diagnosis is clinical and the pathophysiology involves combinations of small-fiber axonopathy, microvasculopathy, inflammation, and brain plasticity/sensitization. Females have much higher risk and workplace accidents are a well-recognized cause. Inflammation and dysimmunity, perhaps facilitated by injury to the blood-nerve barrier, may contribute. Most patients, particularly the young, recover gradually, but treatment can speed healing. Evidence of efficacy is strongest for rehabilitation therapies (e.g., graded-motor imagery), neuropathic pain medications, and electric stimulation of the spinal cord, injured nerve, or motor cortex. Investigational treatments include ketamine, botulinum toxin, immunoglobulins, and transcranial neuromodulation. Nonrecovering patients should be re-evaluated for neurosurgically treatable causal lesions (nerve entrapment, impingement, infections, or tumors) and treatable potentiating medical conditions, including polyneuropathy and circulatory insufficiency. Earlier impressions that CRPS represents malingering or psychosomatic illness have been replaced by evidence that CRPS is a rare complication of limb injury in biologically susceptible individuals.