Peripheral Mechanisms of Ischemic Myalgia

New insight of the efficacy trimetazidine in patients with peripheral arterial disease: a meta-analysis

BACKGROUND

This review aims to examine the impact of trimetazidine on skeletal muscle function in patients suffering from peripheral artery disease (PAD).

METHODS

We searched for studies, both experimental and observational research, concerning the comparison of trimetazidine administration to placebo/standard of care in patients with PAD in PubMed, ScienceDirect, and Cochrane. Meta-analyses of the included studies were performed using Review Manager v5.4. Clinical parameters [ankle-brachial index (ABI) and maximum walking distance (MWD)] were analyzed.

RESULTS

Three observational studies involving 378 participants with PAD satisfied predefined criteria. There was no substantial difference between the examined groups' on ABI (pre- and post-intervention) (MD = - 0.06 [- 0.19 to 0.07], p = 0.38, I2 = 90%). Meanwhile, MWD improvement was significantly higher (MD = 14.15 [6.05-22.25], p = 0.0006, I2 = 37%) in trimetazidine group than in the control group.

CONCLUSIONS

Current evidence from our meta-analysis suggests the beneficial role of trimetazidine's anti-ischemic effect in PAD patients by improving MWD, while it has an insignificant influence on ABI.

Lower Extremity Peripheral Nerve Blocks for Patients at Risk for Acute Compartment Syndrome

A delayed acute compartment syndrome (ACS) diagnosis often results in devastating complications; however, the sensitivity of the classic signs and symptoms is very low. All analgesic modalities have been implicated in delaying the diagnosis, but there is very little evidence linking peripheral nerve blocks (PNBs) with delays in diagnosis. In fact, there is evidence that PNBs may facilitate an early diagnosis; this may be in part due to differences in how ischemic and inflammatory pain is transmitted through unique nociceptive pathways. Collaboration is required to optimize care for patients at risk for ACS.

Sex specific role of RNA-binding protein, AUF1, on prolonged hypersensitivity after repetitive ischemia with reperfusion injury

Repetitive ischemia with reperfusion (I/R) injury is a common cause of myalgia. I/R injuries occur in many conditions that differentially affect males and females including complex regional pain syndrome and fibromyalgia. Our preclinical studies have indicated that primary afferent sensitization and behavioral hypersensitivity due to I/R may be due to sex specific gene expression in the DRGs and distinct upregulation of growth factors and cytokines in the affected muscles. In order to determine how these unique gene expression programs may be established in a sex dependent manner in a model that more closely mimics clinical scenarios, we utilized a newly developed prolonged ischemic myalgia model in mice whereby animals experience repeated I/R injuries to the forelimb and compared behavioral results to unbiased and targeted screening strategies in male and female DRGs. Several distinct proteins were found to be differentially expressed in male and female DRGs, including AU-rich element RNA binding protein (AUF1), which is known to regulate gene expression. Nerve specific siRNA-mediated knockdown of AUF1 inhibited prolonged hypersensitivity in females only, while overexpression of AUF1 in male DRG neurons increased some pain-like responses. Further, AUF1 knockdown was able to specifically inhibit repeated I/R induced gene expression in females but not males. Data suggests that RNA binding proteins like AUF1 may underlie the sex specific effects on DRG gene expression that modulate behavioral hypersensitivity after repeated I/R injury. This study may aid in finding distinct receptor differences related to the evolution of acute to chronic ischemic muscle pain development between sexes.

Contribution of microvascular dysfunction to chronic pain

There is growing evidence that microvascular dysfunction is a pathology accompanying various injuries and conditions that produce chronic pain and may represent a significant contributing factor. Dysfunction that occurs within each component of the microvasculature, including arterioles, capillaries and venules impacts the health of surrounding tissue and produces pathology that can both initiate pain and influence pain sensitivity. This mini review will discuss evidence for a critical role of microvascular dysfunction or injury in pathologies that contribute to chronic pain conditions such as complex regional pain syndrome (CRPS) and fibromyalgia.

Effects of n-3 polyunsaturated fatty acid supplementation on quadriceps weakness immediately after total knee arthroplasty: a pilot, randomized, open-label clinical trial

[Purpose] Severe quadriceps weakness immediately after total knee arthroplasty can be problematic. The n-3 long-chain polyunsaturated fatty acids have antioxidant and anti-inflammatory effects against ischemia-reperfusion injury, whereas n-6 long-chain polyunsaturated fatty acids exert pro-inflammatory effects, thereby promoting ischemia-reperfusion injury. [Participants and Methods] We explored the efficacy of preoperative n-3 long-chain polyunsaturated fatty acid supplementation against early quadriceps weakness among 20 patients scheduled for total knee arthroplasty (intervention group, n=10; control group, n=10). The intervention group received 645 mg of eicosapentaenoic acid) and 215 mg of docosahexaenoic acid daily for 30 days preoperatively. Serum eicosapentaenoic acid, docosahexaenoic acid, and arachidonic acid levels were measured preoperatively. We compared serum derivatives of reactive oxygen metabolites as oxidative stress biomarkers, knee circumference, thigh volume, knee pain during the quadriceps strength test, and quadriceps strength preoperatively and 4 days postoperatively to quantify the change. [Results] Preoperative n-3 long-chain polyunsaturated fatty acid supplementation significantly increased the (eicosapentaenoic acid+docosahexaenoic acid)/arachidonic acid ratio in the intervention group. A significantly lower increase in quadriceps weakness was exhibited in the intervention group than in the control group. However, changes in oxidative stress, knee/thigh swelling, and knee pain during strength testing did not significantly differ between the two groups. [Conclusion] Preoperative n-3 long-chain polyunsaturated fatty acid supplementation exhibited beneficial effects on quadriceps weakness immediately after total knee arthroplasty.

TRPA1 as Target in Myocardial Infarction

Transient receptor potential cation channel subfamily A member 1 (TRPA1), an ion channel primarily expressed on sensory neurons, can be activated by substances occurring during myocardial infarction. Aims were to investigate whether activation, inhibition, or absence of TRPA1 affects infarcts and to explore underlying mechanisms. In the context of myocardial infarction, rats received a TRPA1 agonist, an antagonist, or vehicle at different time points, and infarct size was assessed. Wild type and TRPA1 knockout mice were also compared in this regard. In vitro, sensory neurons were co-cultured with cardiomyocytes and subjected to a model of ischemia-reperfusion. Although there was a difference between TRPA1 activation or inhibition in vivo, no experimental group was different to control animals in infarct size, which also applies to animals lacking TRPA1. In vitro, survival probability of cardiomyocytes challenged by ischemia-reperfusion increased from 32.8% in absence to 45.1% in presence of sensory neurons, which depends, at least partly, on TRPA1. This study raises doubts about whether TRPA1 is a promising target to reduce myocardial damage within a 24 h period. The results are incompatible with relevant enlargements of infarcts by TRPA1 activation or inhibition, which argues against adverse effects when TRPA1 is targeted for other indications.

Inflammation balance in skeletal muscle damage and repair

Responding to tissue injury, skeletal muscles undergo the tissue destruction and reconstruction accompanied with inflammation. The immune system recognizes the molecules released from or exposed on the damaged tissue. In the local minor tissue damage, tissue-resident macrophages sequester pro-inflammatory debris to prevent initiation of inflammation. In most cases of the skeletal muscle injury, however, a cascade of inflammation will be initiated through activation of local macrophages and mast cells and recruitment of immune cells from blood circulation to the injured site by recongnization of damage-associated molecular patterns (DAMPs) and activated complement system. During the inflammation, macrophages and neutrophils scavenge the tissue debris to release inflammatory cytokines and the latter stimulates myoblast fusion and vascularization to promote injured muscle repair. On the other hand, an abundance of released inflammatory cytokines and chemokines causes the profound hyper-inflammation and mobilization of immune cells to trigger a vicious cycle and lead to the cytokine storm. The cytokine storm results in the elevation of cytolytic and cytotoxic molecules and reactive oxygen species (ROS) in the damaged muscle to aggravates the tissue injury, including the healthy bystander tissue. Severe inflammation in the skeletal muscle can lead to rhabdomyolysis and cause sepsis-like systemic inflammation response syndrome (SIRS) and remote organ damage. Therefore, understanding more details on the involvement of inflammatory factors and immune cells in the skeletal muscle damage and repair can provide the new precise therapeutic strategies, including attenuation of the muscle damage and promotion of the muscle repair.

Clinical Characteristics in the Acute Phase of COVID-19 That Predict Long COVID: Tachycardia, Myalgias, Severity, and Use of Antibiotics as Main Risk Factors, While Education and Blood Group B Are Protective

BACKGROUND

Risk factors for developing long COVID are not clearly established. The present study was designed to determine if any sign, symptom, or treatment of the acute phase, or personal characteristics of the patient, is associated with the development of long COVID.

METHODS

A cohort study was carried out, randomly selecting symptomatic COVID-19 patients and not vaccinated. The severity of the acute illness was assessed through the number of compatible COVID-19 symptoms, hospitalizations, and the symptom severity score using a 10-point visual analog scale.

RESULTS

After multivariate analysis, a severity score ≥8 (RR 2.0, 95%CI 1.1-3.5, p = 0.022), hospitalization (RR 2.1, 95%CI 1.0-4.4, p = 0.039), myalgia (RR 1.9, 95%CI 1.08-3.6, p = 0.027), tachycardia (RR 10.4, 95%CI 2.2-47.7, p = 0.003), and use of antibiotics (RR 2.0, 95%CI 1.1-3.5, p = 0.022), was positively associated with the risk of having long COVID. Higher levels of education (RR 0.6, 95%CI 0.4-0.9, p = 0.029) and type positive B blood group (B + AB, RR 0.44, 95%CI 0.2-0.9, p = 0.044) were protective factors. The most important population attributable fractions (PAFs) for long COVID were myalgia (37%), severity score ≥8 (31%), and use of antibiotics (27%).

CONCLUSIONS

Further studies in diverse populations over time are needed to expand the knowledge that could lead us to prevent and/or treat long COVID.

Impact of varying degrees of peripheral nerve blockade on experimental pressure and ischemic pain: adductor canal and sciatic nerve blocks in a human model of compartment syndrome pain

INTRODUCTION

Early diagnosis of acute extremity compartment syndrome is crucial to timely surgical management. Pain is commonly used as an early diagnostic sign for acute extremity compartment syndrome, making regional anesthesia after lower extremity surgery controversial. This randomized study tested whether different concentrations of local anesthetics, or combinations of nerve blocks, would differentially impact the perception of acute extremity compartment syndrome-like pressure and ischemic pain.

METHODS

Healthy volunteers underwent quantitative sensory testing, including determination of pressure pain thresholds and prolonged pressure/ischemic pain in the leg using a variable cuff inflation system. Subjects were randomized to receive (1) adductor canal block alone (ACB), (2) ACB with low-concentration sciatic nerve block (ACB +LC SNB), or (3) ACB with high-concentration SNB (ACB +HC SNB). For the primary outcome, we assessed block-induced increases in pressure threshold to reach 6/10 pain, and compared the degree of increase between the three groups. The main secondary outcome was a comparison of average pain score during a 5 min hold at the 6/10 pressure pain threshold between the three groups.

RESULTS

All blocks raised pressure pain threshold and decreased ischemic pain, but to variable extents. Specifically, the amount the block increased pressure pain threshold was significantly different among ACB, ACB+LC SNB, and ACB+HC SNB groups (mean±SD: 24±32 mm Hg, 120±103 mm Hg, 159±93 mm Hg; p=0.002), with post hoc testing revealing ACB as less than the other two groups. Similarly, average pain scores during a prolonged/ischemic cuff hold differed among the groups (4.2±1.4, 1.4±1.7, 0.4±0.7; p<0.001), with post hoc testing revealing ACB as significantly higher.

DISCUSSION

This study suggests the possible utility of titrating regional anesthesia, to provide some analgesia while still allowing acute extremity compartment syndrome detection.

TRIAL REGISTRATION NUMBER

NCT04113954.

Immediate curative effects of exercise therapy in patients with myalgia of the masticatory muscles

BACKGROUND

Exercise therapy is occasionally considered as an initial treatment for temporomandibular disorders. However, pain can be exacerbated during exercise therapy.

OBJECTIVE

To investigate the immediate curative effects of exercise therapy in patients with masticatory muscle myalgia.

METHODS

Fifty-nine patients with masticatory muscle myalgia were included. Therapists performed exercise therapy (stretched the painful masseter and/or cervical muscles along the direction of muscle contraction) in 10 rounds of traction, each lasting 10 seconds. The patient's pain-free maximum mouth opening distance and degree of pain (VAS value) before and immediately after exercise therapy were compared using the Wilcoxon signed rank test. Mann-Whitney U test was used for the subgroup comparisons.

RESULTS

Mouth opening increased from 41 (IQR 38-43) to 46 (IQR 43-48) mm, and pain alleviation from 48 (IQR 31-56) to 21 (IQR 10-56) immediately following exercise therapy (p < 0.001 for both). None of the patients experienced pain exacerbation or reduction in mouth opening post exercise. No difference in mouth opening distance changes according to sex, painful side, painful site, and therapist were observed (p > 0.05 for all). Pain reduction was greater in patients with unilateral pain (26, IQR 12-39) than those with bilateral (13, IQR 5-25) (p = 0.019). There were no differences in the change in the degree of pain according to sex, painful site, and therapist (p > 0.05 for all).

CONCLUSION

Exercise therapy immediately enlarged the mouth opening distance and reduced myalgia; therefore, it could be helpful in managing masticatory muscle myalgia.

Differential control of blood flow in masseter and biceps brachii muscles during stress

OBJECTIVE

The present study aimed to compare sympathetic hemodynamic effects in masticatory and limb muscles in response to different stressors.

DESIGN

Twelve healthy participants were subjected to a randomized series of stressors, including cold pressor test (CPT), mental arithmetic test, apnea, isometric handgrip (IHG) and post-handgrip muscle ischemia (PHGMI), while in the supine position. Spatially-resolved near-infrared spectroscopy was used to measure relative changes in blood volume and oxygenation (TOI) of the resting masseter and biceps muscles. Cardiac output, heart rate, and arterial blood pressure (ABP) were also monitored.

RESULTS

Except apnea, all tests increased ABP. Different response patterns were observed in the 2 muscles: TOI significantly increased during contralateral IHG (1.24 ± 1.17%) but markedly decreased during CPT (-4.84 ± 4.09%) and PHGMI (-6.65 ± 5.31%) in the biceps muscle, while exhibiting consistent increases in the masseter (1.88 ± 1.85%; 1.60 ± 1.75%; 1.06 ± 3.29%, respectively) (p < 0.05).

CONCLUSIONS

The results allow us to infer differential control of blood flow in head and limb muscles. In general, the masseter appears more prone to dilatation than the biceps, exhibiting opposite changes in response to painful stimuli (CPT and PHGMI). Several mechanisms may mediate this effect, including reduced sympathetic outflow to the extracranial vasculature of the head, generally exposed to lower hydrostatic loads than the rest of the body.

Intermittent Fasting: Potential Utility in the Treatment of Chronic Pain across the Clinical Spectrum

Dietary behavior can have a consequential and wide-ranging influence on human health. Intermittent fasting, which involves intermittent restriction in energy intake, has been shown to have beneficial cellular, physiological, and system-wide effects in animal and human studies. Despite the potential utility in preventing, slowing, and reversing disease processes, the clinical application of intermittent fasting remains limited. The health benefits associated with the simple implementation of a 12 to 16 h fast suggest a promising role in the treatment of chronic pain. A literature review was completed to characterize the physiologic benefits of intermittent fasting and to relate the evidence to the mechanisms underlying chronic pain. Research on different fasting regimens is outlined and an overview of research demonstrating the benefits of intermittent fasting across diverse health conditions is provided. Data on the physiologic effects of intermittent fasting are summarized. The physiology of different pain states is reviewed and the possible implications for intermittent fasting in the treatment of chronic pain through non-invasive management, prehabilitation, and rehabilitation following injury and invasive procedures are presented. Evidence indicates the potential utility of intermittent fasting in the comprehensive management of chronic pain and warrants further investigation.

A functional subdivision within the somatosensory system and its implications for pain research

Somatosensory afferents are traditionally classified by soma size, myelination, and their response specificity to external and internal stimuli. Here, we propose the functional subdivision of the nociceptive somatosensory system into two branches. The exteroceptive branch detects external threats and drives reflexive-defensive reactions to prevent or limit injury. The interoceptive branch senses the disruption of body integrity, produces tonic pain with strong aversive emotional components, and drives self-caring responses toward to the injured region to reduce suffering. The central thesis behind this functional subdivision comes from a reflection on the dilemma faced by the pain research field, namely, the use of reflexive-defensive behaviors as surrogate assays for interoceptive tonic pain. The interpretation of these assays is now being challenged by the discovery of distinct but interwoven circuits that drive exteroceptive versus interoceptive types of behaviors, with the conflation of these two components contributing partially to the poor translation of therapies from preclinical studies.

Disruption of Hyaluronic Acid in Skeletal Muscle Induces Decreased Voluntary Activity via Chemosensitive Muscle Afferent Sensitization in Male Mice

PEGPH20, a human recombinant hyaluronidase, has been proposed as a coadjutant to pancreatic cancer chemotherapy. In early trials, patients reported increased widespread muscle pain as the main adverse reaction to PEGPH20. To understand how PEGPH20 caused musculoskeletal pain, we systemically administered PEGPH20 to male mice and measured voluntary wheel activity and pain-related behaviors. These were paired with ex vivo electrophysiology of primary sensory neurons, whole DRG real-time PCR, and immunohistochemistry of hindpaw muscle. PEGPH20 induced significantly lower wheel running, compared with vehicle-treated animals, and decreased mechanical withdrawal thresholds 5 d after PEGPH20 injections. Chemo-sensory muscle afferents showed increased responses to noxious chemical stimulation of their receptive fields (RFs) in the PEGPH20-treated group. This was correlated with upregulation of the NGF receptor TrkA, the transient receptor potential vanilloid type 1 (TRPV1) channel and ATP-sensitive channel P2X3 in the DRG. Immunohistochemistry of hindpaw muscles revealed damage to the muscle architecture and extensive infiltration of the tissue by cells of the myelomonocytic lineage 3 d after PEGPH20 injection. Peripheral macrophage ablation in macrophage Fas-induced apoptosis (MaFIA) mice, however, did not prevent the decreased voluntary activity and instead caused even lower levels of running. These results suggest that disruption of hyaluronic acid (HA) within the muscle extracellular matrix (ECM) sensitizes chemo-nociceptive muscle afferents possibly leading to altered pain-like behaviors. Ablation experiments suggest macrophages are necessary for adequate recovery of voluntary activity after HA disruption. These data support a role for HA and macrophages in tissue integrity and muscle pain development in patients taking PEGPH20.

Unraveling Muscle Impairment Associated With COVID-19 and the Role of 3D Culture in Its Investigation

COVID-19, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has been considered a public health emergency, extensively investigated by researchers. Accordingly, the respiratory tract has been the main research focus, with some other studies outlining the effects on the neurological, cardiovascular, and renal systems. However, concerning SARS-CoV-2 outcomes on skeletal muscle, scientific evidence is still not sufficiently strong to trace, treat and prevent possible muscle impairment due to the COVID-19. Simultaneously, there has been a considerable amount of studies reporting skeletal muscle damage in the context of COVID-19. Among the detrimental musculoskeletal conditions associated with the viral infection, the most commonly described are sarcopenia, cachexia, myalgia, myositis, rhabdomyolysis, atrophy, peripheral neuropathy, and Guillain-Barré Syndrome. Of note, the risk of developing sarcopenia during or after COVID-19 is relatively high, which poses special importance to the condition amid the SARS-CoV-2 infection. The yet uncovered mechanisms by which musculoskeletal injury takes place in COVID-19 and the lack of published methods tailored to study the correlation between COVID-19 and skeletal muscle hinder the ability of healthcare professionals to provide SARS-CoV-2 infected patients with an adequate treatment plan. The present review aims to minimize this burden by both thoroughly exploring the interaction between COVID-19 and the musculoskeletal system and examining the cutting-edge 3D cell culture techniques capable of revolutionizing the study of muscle dynamics.

Musculoskeletal Problems in Patients with COVID-19: A Review Study

Context: SARS-COV-2 is a coronavirus belonging to the beta-coronavirus group that primarily targets the human respiratory system and causes symptoms similar to those of pneumonia. It should be noted that clinical symptoms of patients with COVID-19 vary in different people. These patients do not only experience respiratory problems. In fact, COVID-19 infection may show a variety of symptoms, including fever, shortness of breath, dry cough, nasal congestion, sore throat, nausea, vomiting, myalgia, arthralgia, fatigue (muscular and mental), joint swelling, headache, diarrhea, as well as some musculoskeletal symptoms. Therefore, the aim of this article was to investigate the major musculoskeletal problems in patients with COVID-19 through a narrative review study. Evidence Acquisition: This study collected the related published studies in the PubMed, ScienceDirect, and Google Scholar sources between 2019 - 2020. The main keywords were COVID-19, coronavirus, and musculoskeletal problems such as muscle fatigue, myalgia, arthralgia, and joint swelling. Results: The major musculoskeletal symptoms included muscle fatigue (25.6%), myalgia and arthralgia (15.5%), joint swelling (as reactive arthritis), and such conditions as joint limitations, tendon shortening, and muscle weakness due to prolonged bed rest. Conclusions: Our findings revealed that attention to musculoskeletal rehabilitation of patients with COVID-19 is as essential as their respiratory rehabilitation. Besides, it would be effective in reducing the physical complications of hospitalization, returning to independence and functional activities, as well as improving the quality of the patients’ life.

TRP channels in COVID-19 disease: Potential targets for prevention and treatment

Coronavirus disease 2019 [COVID-19] is a global health threat caused by severe acute respiratory syndrome coronavirus 2 [SARS-CoV2] that requires two proteins for entry: angiotensin-converting enzyme 2 [ACE2] and -membrane protease serine 2 [TMPRSS2]. Many patients complain from pneumonia, cough, fever, and gastrointestinal (GI) problems. Notably, different TRP channels are expressed in various tissues infected by SARS-CoV-2. TRP channels are cation channels that show a common architecture with high permeability to calcium [Ca²⁺] in most sub-families. Literature review shed light on the possible role of TRP channels in COVID-19 disease. TRP channels may take part in inflammation, pain, fever, anosmia, ageusia, respiratory, cardiovascular, GI and neurological complications related to COVID-19. Also, TRP channels could be the targets for many active compounds that showed effectiveness against SARS-CoV-2. Desensitization or blocking TRP channels by antibodies, aptamers, small molecules or venoms can be an option for COVID-19 prevention and future treatment. This review provides insights into the involvement of TRP channels in different symptoms and mechanisms of SARS-CoV-2 , potential treatments targeting these channels and highlights missing gaps in literature.

Identification of a population of peripheral sensory neurons that regulates blood pressure

The vasculature is innervated by a network of peripheral afferents that sense and regulate blood flow. Here, we describe a system of non-peptidergic sensory neurons with cell bodies in the spinal ganglia that regulate vascular tone in the distal arteries. We identify a population of mechanosensitive neurons, marked by tropomyosin receptor kinase C (TrkC) and tyrosine hydroxylase in the dorsal root ganglia, which projects to blood vessels. Local stimulation of TrkC neurons decreases vessel diameter and blood flow, whereas systemic activation increases systolic blood pressure and heart rate variability via the sympathetic nervous system. Ablation of the neurons provokes variability in local blood flow, leading to a reduction in systolic blood pressure, increased heart rate variability, and ultimately lethality within 48 h. Thus, a population of TrkC⁺ sensory neurons forms part of a sensory-feedback mechanism that maintains cardiovascular homeostasis through the autonomic nervous system.

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TrkC⁺/Th⁺ DRG neurons project to blood vessels

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Local stimulation of TrkC⁺ DRG neurons decreases vessel diameter and blood flow

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Systemic activation of TrkC⁺ DRG neurons increases blood pressure and heart rate

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Ablation of TrkC⁺ neurons dysregulates cardiovascular homeostasis and is lethal

Pain Symptoms in Patients with Coronavirus Disease (COVID-19): A Literature Review

Purpose

On 11 March, 2020, the coronavirus disease (COVID-19) outbreak was declared as a global pandemic by the World Health Organization. It brought substantial physical and psychological burden on individuals and financial loss across countries. Patients with COVID-19 may exhibit various symptoms, such as fever, cough, dyspnea, muscle pain, sore throat, headache, chest pain, and abdominal pain, at 2–14 days after exposure to the novel coronavirus (severe acute respiratory syndrome [SARS]-CoV-2). Pain symptoms present important challenge to clinicians’ diagnosis when treating COVID-19 patients with mild symptoms. Considering the increasing number of confirmed COVID-19 cases, the pain symptoms should be systematically summarized.

Results

The virus can invade different tissues of the body and cause different pain manifestations. SARS-CoV-2 primarily invades the respiratory system, and patients develop sore throat, fever, cough, and other pneumonia-associated symptoms. Moreover, it infects the nervous system (eg, headache, dizziness, and confusion), digestive system (eg, abdominal pain, diarrhea), and cardiovascular system (eg, chest pain, palmus, and cardiac injury). The incidence rate is 1.7–33.9% for headache, 0.7–47.1% for sore throat, 1.5–61.0% for myalgia/arthralgia, 1.6–17.7% for chest pain, and 1.9–14.5% for abdominal pain. In comparison with chest and abdominal pain, COVID-19 patients are more likely to develop headache, sore throat, and myalgia/arthralgia.

Conclusion

Different pain reflects the damage of different body systems. Therefore, the summary of pain symptoms for COVID-19 patients can help doctors improve the accuracy and efficiency of diagnosis when treating COVID-19 patients with atypical or mild symptoms and adopt more targeted treatment methods.

Assessment of musculoskeletal pain, fatigue and grip strength in hospitalized patients with COVID-19

BACKGROUND

Although there are some retrospective studies to present musculoskeletal findings of the COVID-19, still the muscle strength and fatigue has not been studied in detail.

AIM

To reveal the symptoms of musculoskeletal system in COVID-19 patients, to evaluate myalgia, arthralgia and physical/mental fatigue, to assess handgrip muscle strength, and to examine the relations of these parameters with the severity and laboratory values of the disease.

DESIGN

This study was designed as a cross-sectional, single-center case series.

SETTING

This study took place from May 15, 2020, to June 30, 2020 at the Istanbul University-Cerrahpasa, Cerrahpasa Pandemia Services.

POPULATION

Hospitalized 150 adults with laboratory and radiological confirmation of severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) according to WHO interim guidance were included in the study.

METHODS

The disease severity 2007 IDSA/ATS guidelines for community acquired pneumonia was used. Myalgia severity was assessed by numerical rating scale (NRS). Visual analog scale and Chalder Fatigue Scale (CFS) were used for fatigue severity determination. Handgrip strength (HGS) was measured by Jamar hand dynamometer.

RESULTS

One hundred three patients (68.7%) were non-severe, and 47 patients (31.3%) were severe. The most common musculoskeletal symptom was fatigue (133 [85.3%]), followed by myalgia (102 [68.0%]), arthralgia (65 [43.3%]) and back pain (33 [22.0%]). Arthralgia, which was mostly notable at wrist (25 [16.7%]), ankle (24 [16.0%]) and knee (23 [15.3%]) joints, was significantly higher among the severe group. Severe myalgia was prevalent among myalgia sufferers regardless of COVID-19 severity. The physical fatigue severity score was significantly higher in severe cases, whereas this difference was not significant in mental fatigue score. Female patients with severe infection had "lower" grip strength, whereas grip strength among males did not differ significantly between non-severe and severe COVID-19 cases. Nevertheless, the mean values in both genders and in age decades were below the specified normative values. CRP, ferritin, and LDH levels were significantly higher in women with "lower" grip strength compared to the "normal" group.

CONCLUSIONS

Aside from other multisystemic symptoms, musculoskeletal symptoms are quite common in patients with COVID-19. Patients have severe ischemic myalgia regardless of disease activity. Although there is a muscle weakness in all patients, the loss of muscle function is more of a problem among women in connection with disease severity. Muscular involvement in Coronavirus disease is a triangle of myalgia, physical fatigue, and muscle weakness.

CLINICAL REHABILITATION IMPACT

Muscle involvement in COVID-19 patients does not mean only myalgia but also a combination of physical fatigue and muscle weakness, and this should be considered in planning the rehabilitation strategies of COVID-19 patients.

Nerve growth factor in muscle afferent neurons of peripheral artery disease and autonomic function

In peripheral artery disease patients, the blood supply directed to the lower limbs is reduced. This results in severe limb ischemia and thereby enhances pain sensitivity in lower limbs. The painful perception is induced and exaggerate during walking, and is relieved by rest. This symptom is termed by intermittent claudication. The limb ischemia also amplifies autonomic responses during exercise. In the process of pain and autonomic responses originating exercising muscle, a number of receptors in afferent nerves sense ischemic changes and send signals to the central nervous system leading to autonomic responses. This review integrates recent study results in terms of perspectives including how nerve growth factor affects muscle sensory nerve receptors in peripheral artery disease and thereby alters responses of sympathetic nerve activity and blood pressure to active muscle. For the sensory nerve receptors, we emphasize the role played by transient receptor potential vanilloid type 1, purinergic P2X purinoceptor 3 and acid sensing ion channel subtype 3 in amplified sympathetic nerve activity responses in peripheral artery disease.

Effects of preoperative low-intensity training with slow movement on early quadriceps weakness after total knee arthroplasty in patients with knee osteoarthritis: a retrospective propensity score-matched study

Background

Severe and early quadriceps weakness (QW) after total knee arthroplasty (TKA), which is caused by acute inflammation resulting from surgical trauma and tourniquet-induced ischemia-reperfusion (IR) injury, can be especially problematic. We focused on tourniquet-induced IR injury, because it has been shown to be preventable through ischemic and exercise preconditioning. Low-intensity resistance exercise with slow movement and tonic force generation (LST) share some similarities with ischemic and exercise preconditioning. The present study primarily aimed to clarify the efficacy of preoperative LST program as prehabilitation for early QW among patients with TKA using propensity score matching analysis.

Methods

This single-center retrospective observational study used data from patients with knee osteoarthritis (n = 277) who were scheduled to undergo unilateral TKA between August 2015 and January 2017. Those with missing outcome data due to their inability to perform tests were excluded. The LST group included participants who performed LST and aerobic exercise (LST session) more than seven times for three months prior to surgery. The control group included participants who performed less than eight LST sessions, a general and light exercise or had no exercise for three months prior to surgery. Knee circumference, thigh volume, knee pain during quadriceps strength test (QST) and timed up and go test (TUG), quadriceps strength, and TUG were measured before and 4 days after surgery. Knee swelling, thigh swelling, Δknee pain, QW, and ΔTUG were determined by comparing pre- and postoperative measurements.

Results

Propensity score matching generated 41 matched pairs who had nearly balanced characteristics. The LST group had a significantly lower knee and thigh swelling, QW, and ΔTUG compared to the control group (all, p < 0.05). No significant differences in Δknee pain during the QST and TUG were observed between both groups (both, p > 0.05).

Conclusions

The present study demonstrated the beneficial effects of preoperative LST program on knee swelling, thigh swelling, QW, and walking disability immediately after TKA.

Ischemic Pain

This article discusses the pathophysiology, presentation, cause, and treatment of ischemic pain in the surgical patient. Causes of ischemic pain vary but all fundamentally cause local acidosis in the peripheral tissues, which causes signals to be passed through ascending pain pathways to the thalamus and eventual cerebral cortex where it is interpreted as ischemic pain. Ischemic pain is classically associated with an insidious onset but can present in the acute or chronic setting. Treatments are aimed at improving perfusion to the affected tissue. Surgical options include repairing damaged vessels, bypassing diseased vessels, performing thrombectomy, or embolectomy. Numerous conservative therapies exist.

Myofascial Trigger Points Therapy Modifies Thermal Map of Gluteal Region

Background

Thermal imaging may be effectively used in musculoskeletal system diagnostics and therapy evaluation; thus, it may be successfully applied in myofascial trigger points assessment.

Objective

Investigation of thermal pattern changes after myofascial trigger points progressive compression therapy in healthy males and females.

Methods

The study included 30 healthy people (15 females and 15 males) with age range 19–34 years (mean age: 23.1 ± 4.21). Thermograms of myofascial trigger points were taken pre- and posttherapy and consecutively in the 15^th and 30^th minutes. Pain reproducible by palpation intensity was assessed with numeric rating scale.

Results

Progressive compression therapy leads to myofascial trigger points temperature (p=0.02) and surface (p=0.02) and surface (p=0.02) and surface (p=0.02) and surface (

Conclusions

The study indicates that myofascial trigger points reaction to applied therapy spreads in time and space and depends on participants' sex.

A dual role for peripheral GDNF signaling in nociception and cardiovascular reflexes in the mouse

Group III/IV muscle afferents transduce nociceptive signals and modulate exercise pressor reflexes (EPRs). However, the mechanisms governing afferent responsiveness to dually modulate these processes are not well characterized. We and others have shown that ischemic injury can induce both nociception-related behaviors and exacerbated EPRs in the same mice. This correlated with primary muscle afferent sensitization and increased expression of glial cell line-derived neurotrophic factor (GDNF) in injured muscle and increased expression of GDNF family receptor α1 (GFRα1) in dorsal root ganglia (DRG). Here, we report that increased GDNF/GFRα1 signaling to sensory neurons from ischemia/reperfusion-affected muscle directly modulated nociceptive-like behaviors and increased exercise-mediated reflexes and group III/IV muscle afferent sensitization. This appeared to have taken effect through increased cyclic adenosine monophosphate (cAMP) response element binding (CREB)/CREB binding protein-mediated expression of the purinergic receptor P2X5 in the DRGs. Muscle GDNF signaling to neurons may, therefore, play an important dual role in nociception and sympathetic reflexes and could provide a therapeutic target for treating complications from ischemic injuries.

Chronic non-inflammatory muscle pain: central and peripheral mediators

Conditions with chronic widespread non-inflammatory muscle pain, such as fibromyalgia, have complex etiologies with numerous proposed mechanisms for their pathophysiology of underlying chronic pain. Advancements in neuroimaging have allowed for the study of brain function and connectivity in humans with these conditions, while development of animal models have allowed for the study of both peripheral and central factors that lead to chronic pain. This article reviews the current literature surrounding the pathophysiology of chronic widespread non-inflammatory muscle pain focusing on both peripheral and central nervous system, as well as immune system, contributions to the development and maintenance of pain. A better understanding of the mechanisms underlying these conditions can allow for improvements in patient education, treatment and outcomes.

Nerve growth factor-induced muscle hyperalgesia facilitates ischaemic contraction-evoked pain

BACKGROUND

Intramuscular injection of Nerve Growth Factor (NGF) may influence the responsiveness of active chemo-sensitive channels affecting muscle pain sensitivity. This double-blinded crossover study in healthy humans assessed contraction-evoked pain responses and pain sensitivity during acute ischaemia in the tibialis anterior (TA) muscle before and 24 hr after five distributed NGF injections (1 µg, 4 cm interval) compared with control injections (isotonic-saline).

METHODS

Twenty-one subjects participated in two experimental phases, each including five sessions over 7 days, with a gap of 4 weeks in-between. Muscle pain intensity evoked with daily functional tasks (Likert scale score) was collected using a paper diary. Pain intensity evoked by ischaemic and non-ischaemic contractions numerical rating scale (NRS) was collected at Day0 and Day1. Pressure pain thresholds (PPTs) on the TA were recorded before (Day0), 3 hr, 1, 3, and 7 days post-injection, and after the ischaemic-contractions and post-cuff deflation at Day0 and Day1.

RESULTS

Increased Likert scores of pain were present for 7 days after NGF compared to control injections (p < .05). Higher NRS pain scores of ischaemic-contractions were seen when contracting the muscle injected with NGF compared to baseline (p = .003) and control (p = .012). Pain during non-ischaemic contractions was not significantly affected by NGF injections. Decreased PPTs were found at 3 hr, Day1 and Day3 post-injection (p < .05) in both conditions. Compared with pre-contractions, PPTs were increased following ischaemic contractions at Day0 (p < .05) and Day1 (p < .05) in both conditions.

CONCLUSION

This study showed that ischaemic contraction-evoked pain was facilitated in an NGF-sensitized muscle.

SIGNIFICANCE

Acidification of the muscle environment may affect muscle nociceptors and pain by different mechanisms, including activation of ASIC₃ and TRPV1. In this study, pain evoked following ischaemic contractions was increased in the Nerve Growth Factor (NGF)-sensitized muscle compared with non-ischaemic contractions and in the non-sensitized muscle. These findings illustrate that responses of peripheral afferents under ischaemic conditions are altered by a pre-sensitized muscle. This highlights the role of growth factors, including NGF, in peripheral muscle sensitization with clinical implications for ischaemic myalgia.

The Development of a Macromolecular Analgesic for Arthritic Pain

The addictive potential of clinically used opioids as a result of their direct action on the dopaminergic reward system in the brain has limited their application. In an attempt to reduce negative side effects as well as to improve the overall effectiveness of these analgesics, we have designed, synthesized, and evaluated an N-(2-hydroxypropyl)methacrylamide (HPMA)-based macromolecular prodrug of hydromorphone (HMP), a commonly used opioid. To this end, P-HMP was synthesized via RAFT polymerization and a subsequent polymer analogous reaction. Its interaction with inflammatory cells in arthritic joints was evaluated in vitro using a RAW 264.7 cell culture, and subsequent confocal microscopy analysis confirmed that P-HMP could be internalized by the cells via endocytosis. In vivo imaging studies indicated that the prodrug can passively target the arthritic joint after systemic administration in a rodent model of monoarticular adjuvant-induced arthritis (MAA). The inflammatory pain-alleviating properties of the prodrug were assessed in MAA rats using the incapacitance test and were observed to be similar to dose-equivalent HMP. Analgesia through mechanisms at the spinal cord level was further measured using the tail flick test, and it was determined that the prodrug significantly reduced spinal cord analgesia versus free HMP, further validating the peripheral restriction of the macromolecular prodrug. Immunohistochemical analysis of cellular uptake of the P-HMP within the MAA knee joint proved the internalization of the prodrug by phagocytic synoviocytes, colocalized with HMP's target receptor as well as with pain-modulating ion channels. Therefore, it can be concluded that the novel inflammation-targeting polymeric prodrug of HMP (P-HMP) has the potential to be developed as an effective and safe analgesic agent for musculoskeletal pain.

A-Type KV Channels in Dorsal Root Ganglion Neurons: Diversity, Function, and Dysfunction

A-type voltage-gated potassium (Kv) channels are major regulators of neuronal excitability that have been mainly characterized in the central nervous system. By contrast, there is a paucity of knowledge about the molecular physiology of these Kv channels in the peripheral nervous system, including highly specialized and heterogenous dorsal root ganglion (DRG) neurons. Although all A-type Kv channels display pore-forming subunits with similar structural properties and fast inactivation, their voltage-, and time-dependent properties and modulation are significantly different. These differences ultimately determine distinct physiological roles of diverse A-type Kv channels, and how their dysfunction might contribute to neurological disorders. The importance of A-type Kv channels in DRG neurons is highlighted by recent studies that have linked their dysfunction to persistent pain sensitization. Here, we review the molecular neurophysiology of A-type Kv channels with an emphasis on those that have been identified and investigated in DRG nociceptors (Kv1.4, Kv3.4, and Kv4s). Also, we discuss evidence implicating these Kv channels in neuropathic pain resulting from injury, and present a perspective of outstanding challenges that must be tackled in order to discover novel treatments for intractable pain disorders.

Selective Prostacyclin Receptor Agonist Selexipag, in Contrast to Prostacyclin Analogs, Does Not Evoke Paradoxical Vasoconstriction of the Rat Femoral Artery

Selexipag [2-{4-[(5,6-diphenylpyrazin-2-yl)(isopropyl)amino]butoxy}-N-(methylsulfonyl)acetamide] is a selective nonprostanoid prostacyclin (PGI₂) receptor (IP receptor) agonist that is approved for the treatment of pulmonary arterial hypertension (PAH). In contrast to selexipag, PGI₂ analogs used in the clinic are nonselective agonists at prostanoid receptors and can also activate contractile prostaglandin E receptor 3 (EP₃) receptors. Leg pain is a common side effect in patients receiving treatment with PGI₂ analogs and peripheral vasoconstriction can be responsible for side effects related to muscular ischemia. This study tested the hypothesis that PGI₂ analogs could cause paradoxical vasoconstriction of the femoral artery via EP₃ receptor activation but that only vasorelaxation would be observed in response to selexipag and its active metabolite ACT-333679 [{4-[(5,6-diphenylpyrazin-2-yl)(isopropyl)amino]butoxy}acetic acid]. Selexipag and ACT-333679 relaxed rings of the isolated rat femoral artery contracted with either prostaglandin F_2α (PGF_2α ) or the α₁ adrenoceptor (α₁AR) agonist phenylephrine. ACT-333679 also inhibited contraction of the femoral artery to sympathetic nerve stimulation. In contrast, PGI₂ analogs (iloprost, beraprost, and treprostinil) caused additional contraction of arterial rings precontracted with phenylephrine, which was reverted to relaxation by antagonism of EP₃ receptors. Treprostinil augmented contraction of the femoral artery to sympathetic nerve stimulation in an EP₃ receptor-dependent manner. Mechanistically, concomitant EP₃ and α₁AR receptor activation synergistically constricted femoral arteries. It is concluded that selexipag and ACT-333679 are vasorelaxants of the rat femoral artery and, unlike PGI₂ analogs, do not cause paradoxical vasoconstriction via activation of EP₃ receptors. EP₃ receptor-mediated vasoconstriction may contribute to the well documented peripheral muscle pain reported in patients with PAH receiving PGI₂ analogs. Leg pain may be less in patients treated with selexipag.