Structural and functional motor cortex asymmetry in unilateral lower limb amputation with phantom limb pain

Pain modulation in amputees: Exploring conditioned pain modulation and its influencing factors on amputated and non-amputated sides: A cross-sectional study

Background

Amputation leads to significant physical, psychological, and emotional challenges, with chronic pain being among the most debilitating outcomes. Conditioned Pain Modulation (CPM) is a key mechanism for understanding pain modulation reflecting the central nervous system's capacity to regulate pain.

Objective

This study aimed to evaluate CPM in amputees, comparing CPM between the amputated and non-amputated sides, and to identify factors influencing CPM in this population.

Method

Eighty-six amputees participated in the study. Sociodemographic and pain-related variables, including age, occupation, smoking status, pre-amputation pain duration, phantom limb pain, and pressure pain threshold, were assessed. Multiple linear regression models were performed to explore factors associated with CPM on both sides, with additional t-tests to compare CPM values between sides.

Results

The multivariate model for the amputated side explained 26.3% of CPM variability, with significant associations found for pre-amputation pain duration and retirement status, as well as PPT mean of the amputated side, smoking, and phantom limb pain and age. In contrast, the non-amputated side model explained 26.5% (Adjusted R-squared) of the variability, with the following significant variables: duration of pre-amputation pain (negative correlation), smoking history, phantom limb pain (negative correlation), and frequency of telescoping sensation (negative correlation). There were no significant differences in CPM between amputated and non-amputated sides (p > 0.05).

Conclusion

The findings suggest that CPM on the amputated side is more influenced by pain experience and sociodemographic variables, while the non-amputated side shows less variability and is more resilient to these influences.

Neurophysiological Markers of Adaptation and Compensation Following Lower Limb Amputation: An Analysis of EEG Oscillations and Clinical Predictors from the DEFINE Cohort Study

Background: Neuroplasticity, involving cortical and subcortical reorganization, plays a critical role in the adaptation and compensation process post-amputation. However, underlying neurophysiological changes remain unclear, particularly in brain oscillations. Methods: This is a cross-sectional analysis that includes baseline data from 48 individuals with lower limb amputation from our DEFINE Cohort Study project. EEG data were collected using a 64-channel system during a 5-min resting-state period. Preprocessed data were analyzed for delta and alpha oscillations across frontal, central, and parietal regions. Logistic regression models examined associations between EEG oscillations and clinical variables, including cognition (MoCA), functional independence (FIM), and phantom limb sensations (PLS). Results: The multivariate logistic regression analysis revealed distinct patterns of association between EEG oscillations and clinical variables. Delta oscillations were inversely associated with cognitive scores (OR: 0.69; p = 0.048), while higher delta power was related to the absence of PLS (OR: 58.55; p < 0.01). Frontal alpha power was positively linked to cognitive function (OR: 1.55; p = 0.02) but negatively associated with functional independence (OR: 0.75; p = 0.04). Conclusions: These findings suggest that lower frequencies, such as delta oscillations, play a role as potential compensatory brain rhythms. In contrast, alpha oscillations may reflect a more adapted pattern of brain reorganization after amputation.

Alterations in spontaneous brain activity of maintenance hemodialysis patients with restless legs syndrome: a cross-sectional case-control study

OBJECTIVE

Through resting state functional magnetic resonance imaging (rs-fMRI) we evaluate the spontaneous brain activity changes of maintenance hemodialysis (MHD) patients with restless legs syndrome (RSL) and analyzed the imaging features and related mechanisms of RLS in patients with MHD.

METHOD

We select 27 MHD patients with RLS and 27 patients without RSL matched by age, gender, cognitive function. Both groups underwent neuropsychological tests and MRI scans. MRI data analysis was performed to obtain and compare the amplitude of low-frequency fluctuation (ALFF), fractional amplitude of low-frequency fluctuations (fALFF), and regional homogeneity (ReHo) values, which were mALFF, mfALFF, and mReHo. Clinical data were collected and compared. Differentiated indicators and RLS scores conduct Pearson correlation analysis.

RESULT

Compared with the MHD-nRLS group, the MHD-RLS group showed significantly lower mALFF values in the left precentral, right precentral gyrus, and right postcentral gyrus, lower mfALFF values in the left precentral gyrus, right precentral gyrus, left calcarine fissure, left lingual gyrus, left postcentral gyrus, and right postcentral gyrus, and lower mReHo values in the left precentral gyrus, right precentral gyrus, left calcarine fissure, left lingual gyrus, left postcentral gyrus, and right postcentral gyrus, and right postcentral gyrus (P < 0.05). The MHD-RLS group exhibited lower hemoglobin levels (P = 0.001), higher total iron-binding capacity levels (P = 0.011), and higher folic acid levels (P = 0.022). The above indicators were correlated with RLS scores using Pearson correlation analysis, and it was found that the mfALFF value of the right precentral gyrus and the right postcentral gyrus, and the mReHo values of the right precentral gyrus and right postcentral gyrus were negatively correlated with the RLS score (r = -0.567, P = 0.002;r = -0.705, P < 0.001;r = -0.414, P = 0.032; r = -0.410, P = 0.034), and the hemoglobin concentration was negatively correlated with the RLS scores (r = -0.394, P = 0.042).

CONCLUSION

Patients with MHD-RLS exhibit abnormal spontaneous brain activity in the right precentral gyrus and right postcentral gyrus within the sensorimotor network, along with lower hemoglobin levels, which may be associated with the pathogenesis and severity of MHD-RLS.

Disruptive compensatory mechanisms in fibromyalgia syndrome and their association with pharmacological agents

Fibromyalgia syndrome (FMS) is a chronic disorder characterized commonly by widespread musculoskeletal pain and fatigue, predominantly affecting women, with its complexity often leading to underdiagnosis and complicating treatment effectiveness. Transcranial magnetic stimulation (TMS) metrics are potential markers to optimize FMS treatments; however, evidence is limited. Our study aimed to explore the relationship between cortical excitability and inhibition, assessed through TMS markers, and clinical characteristics in patients with FMS. This presented cross-sectional study employed baseline data from a clinical trial with 108 FMS patients, mostly female (88.8%), and mean age of 47.3 years old (SD = 12.06). Our analysis showed that decreased short-intracortical inhibition (SICI) was associated with gabapentinoids use, nicotine history, and increased fatigue levels, suggesting its connection with compensatory mechanisms for non-painful FMS features. Increased motor intracortical facilitation (ICF) was linked with greater pain severity and shorter FMS duration, implying its relationship with a reorganization of sensorimotor pathways due to chronic pain. Additionally, higher resting motor threshold (rMT) was associated with less effective pain modulation (lower conditioned pain modulation [CPM]), indicating a disruption of pain compensatory mechanism. Given the role of SICI in indexing homeostatic brain mechanisms and its association with fatigue, a hallmark characteristic of FMS-induced behavioral changes, these results suggest that FMS likely has a deleterious effect on brain inhibitory function, thus providing a potential novel insight for FMS mechanisms. In addition, it seems that this compensatory mechanism's disruption is enhanced by pharmacological agents such as gabapentioids and nicotine.

Neural correlates of phantom motor execution: A functional neuroimaging systematic review and meta-analysis

Phantom motor execution (PME) shows promise as a new treatment for phantom limb pain (PLP) by inducing motor-related analgesia and retraining the pain network activation. However, the current understanding of the neural correlates underlying PME is limited. Databases were systematically searched for multimodal neuroimaging studies to explore the neural correlates of PME. A narrative synthesis (17 studies, n = 328) and coordinate-based meta-analysis were performed to identify activation commonalities. Contrasting PME-vs-REST revealed differential activation of the supplementary motor area (SMA), post-central gyrus, and dorsolateral superior frontal gyrus; while PME-vs-ME revealed differential activation of the right anterior insula, anterior cingulate, left amygdala, and right striatum. Further narrative synthesis revealed a positive correlation between PME-induced brain activity and PLP intensity, and a specific connectivity pattern during PME on the SMA-M1 network compared to ME and motor imagery. Our results suggest that the PME represents a distinct type of motor network activation, partially overlapping with ME and motor imagery activations but with special activation of interoceptive regulation and mood-related regions. Thus, confirming its potential as a therapeutic approach for PLP.

Neuropsychiatric drugs and a neurophysiological marker as predictors of health-related quality of life in patients with phantom limb pain

OBJECTIVE

To explore the relationship between sociodemographic, clinical, and neurophysiological variables and health-related quality of life (HR-QOL) of patients with phantom limb pain (PLP).

METHODS

This is a cross-sectional analysis of a previous clinical trial. Univariate and multivariate linear and logistic regression analyses were used to model the predictors of HR-QOL. We utilized a sequential modeling approach with increasing adjustment levels, controlling for age and sex, and other relevant clinical variables (time since amputation, level of amputation, and pain). HR-QOL was assessed by the SF-36 Health Survey and its 8 subdomains.

RESULTS

We analyzed baseline data from 92 patients with lower-limb amputations. They were mostly male (63%), 45.2 ± 15.6 years, with a mean time since amputation of 82.7 ± 122.4 months, and an overall SF-36 score of 55.9 ± 21.5. We found an association between intracortical facilitation (ICF) in the affected hemisphere, gabapentin usage, and HR-QOL. ICF is a predictor of better HRQOL, whereas gabapentin usage was associated with a poorer HR-QOL, with the main model explaining 13.4% of the variance in the outcome. For the SF-36 subdomains, ICF was also a positive predictor for social functioning, bodily pain, and vitality, while medication usage was associated with lower scores in mental health, general health perception, bodily pain, and vitality.

CONCLUSION

We found firsthand 2 new independent predictors of HR-QOL in individuals with PLP, namely, the neurophysiological metric ICF and gabapentin usage. These results highlight the role of the motor cortex excitability in the HR-QOL and stress the need for treatments that favor the neuroplastic adaptation after amputation, for which ICF may be used as a possible marker.

The Endogenous Pain Modulatory System as a Healing Mechanism: A Proposal on How to Measure and Modulate It

BACKGROUND

Chronic pain is highly burdening and multifactorial in etiology. The endogenous-pain-healing system restores body tissue to a non-painful state after an injury leading to pain, and its disruption could represent a relevant mechanism, especially for nursing interventions.

AIM

To review the literature and summarize the results that support this hypothesis.

METHODS

We hypothesized that the mechanism behind this system mainly depends on the endogenous pain modulatory system (EPMS), which is responsible for inhibiting pain after tissue healing is complete and facilitating it when tissue damage is still present. Different biomarkers can quantify EPMS functioning. We reviewed the literature and included relevant information regarding this hypothesis.

RESULTS

First, conditioned pain modulation (CPM) measures pain inhibition and is a possible predictor for pain chronification. Second, motor cortex excitability measures the cortical control of the EPMS, which can be assessed through transcranial magnetic stimulation (using intracortical inhibition) or electroencephalography. Modifiable factors disrupt its functioning, such as sleep deprivation, medication overuse, and mental health status, but could be protective, such as exercise, certain medications, mind-body techniques, and non-invasive neuromodulation therapies. The acquisition of neurophysiological knowledge of how the chronicity of pain occurs and the EPMS involvement in this process may allow for better management of these patients.

CONCLUSIONS

We raised the hypothesis that the impairment of the EPMS (altered cortical excitability and descendent pain modulation pathways) seems to be related to the disruption of the pain healing process and its chronicity. Further longitudinal studies evaluating the relationship between these biomarkers and chronic pain development are necessary.

The Impact of Obesity as a Peripheral Disruptor of Brain Inhibitory Mechanisms in Fibromyalgia: A Cross-Sectional Study

Background/Objective: Obesity, characterized by chronic inflammation, may serve as a surrogate marker for more dysfunctional peripheral inflammation, potentially exacerbating FM symptomatology. Given this premise, this study aimed to investigate the effects of obesity as an effect modifier on neural and clinical variables, specifically those indexing pain-compensatory mechanisms in FM symptoms. Methods: A cross-sectional study was conducted with 108 participants who underwent a standardized TMS protocol assessment to measure resting motor threshold (MT), intracortical facilitation (ICF), and intracortical inhibition (ICI). Clinical data were collected using Beck's Depression Index (BDI), PROMIS, the Brief Pain Inventory (BPI), and conditioned pain modulation (CPM). Linear regression models were used to explore the relationship between these variables while examining Body Mass Index (BMI) as a potential effect modifier. If it was found to be a modifier, we stratified the sample into two groups with a BMI cutoff of 30 and performed another regression model within the subgroups. Results: BMI was identified as an effect modifier in the relationships between ICI and BDI, PROMIS fatigue, and CPM and in MT versus CPM. After stratification, non-obese fibromyalgia subjects demonstrated significant correlations between clinical symptoms and CPM and ICI activity. However, these correlations were absent in the obese group, suggesting obesity disrupts pain mechanisms and their compensatory effects. Higher MT values were associated with weaker endogenous pain control, particularly evident in the obese group. Conclusions: Obesity appears to be a significant effect modifier and delineates two patient groups across multiple clinical and neural assessments of fibromyalgia. Additionally, it suggests a role for obesity in exacerbating fibromyalgia symptoms and disrupting physiological pain-inhibitory mechanisms.

Real-time motion-enabling positron emission tomography of the brain of upright ambulatory humans

BACKGROUND

Mobile upright PET devices have the potential to enable previously impossible neuroimaging studies. Currently available options are imagers with deep brain coverage that severely limit head/body movements or imagers with upright/motion enabling properties that are limited to only covering the brain surface.

METHODS

In this study, we test the feasibility of an upright, motion-compatible brain imager, our Ambulatory Motion-enabling Positron Emission Tomography (AMPET) helmet prototype, for use as a neuroscience tool by replicating a variant of a published PET/fMRI study of the neurocorrelates of human walking. We validate our AMPET prototype by conducting a walking movement paradigm to determine motion tolerance and assess for appropriate task related activity in motor-related brain regions. Human participants (n = 11 patients) performed a walking-in-place task with simultaneous AMPET imaging, receiving a bolus delivery of F18-Fluorodeoxyglucose.

RESULTS

Here we validate three pre-determined measure criteria, including brain alignment motion artifact of less than <2 mm and functional neuroimaging outcomes consistent with existing walking movement literature.

CONCLUSIONS

The study extends the potential and utility for use of mobile, upright, and motion-tolerant neuroimaging devices in real-world, ecologically-valid paradigms. Our approach accounts for the real-world logistics of an actual human participant study and can be used to inform experimental physicists, engineers and imaging instrumentation developers undertaking similar future studies. The technical advances described herein help set new priorities for facilitating future neuroimaging devices and research of the human brain in health and disease.

Pain in the Context of Sensory Deafferentation

Pain that accompanies deafferentation is one of the most mysterious and misunderstood medical conditions. Prevalence rates for the assorted conditions vary considerably but the most reliable estimates are greater than 50% for strokes involving the somatosensory system, brachial plexus avulsions, spinal cord injury, and limb amputation, with controversy surrounding the mechanistic contributions of deafferentation to ensuing neuropathic pain syndromes. Deafferentation pain has also been described for loss of other body parts (e.g., eyes and breasts) and may contribute to between 10% and upwards of 30% of neuropathic symptoms in peripheral neuropathies. There is no pathognomonic test or sign to identify deafferentation pain, and part of the controversy surrounding it stems from the prodigious challenges in differentiating cause and effect. For example, it is unknown whether cortical reorganization causes pain or is a byproduct of pathoanatomical changes accompanying injury, including pain. Similarly, ascertaining whether deafferentation contributes to neuropathic pain, or whether concomitant injury to nerve fibers transmitting pain and touch sensation leads to a deafferentation-like phenotype can be clinically difficult, although a detailed neurologic examination, functional imaging, and psychophysical tests may provide clues. Due in part to the concurrent morbidities, the physical, psychologic, and by extension socioeconomic costs of disorders associated with deafferentation are higher than for other chronic pain conditions. Treatment is symptom-based, with evidence supporting first-line antineuropathic medications such as gabapentinoids and antidepressants. Studies examining noninvasive neuromodulation and virtual reality have yielded mixed results.

Distinct patterns of metabolic motor cortex activity for phantom and residual limb pain in people with amputations: A functional near-infrared spectroscopy study

BACKGROUND

Phantom pain limb (PLP) has gained more attention due to the large number of people with amputations around the world and growing knowledge of the pain process, although its mechanisms are not completely understood.

OBJECTIVES

The aim of this study was to understand, in patients with amputations, the association between PLP and residual limb pain (RLP), and the brain metabolic response in cortical motor circuits, using functional near-infrared spectroscopy (fNIRS).

METHODS

Sixty participants were recruited from the rehabilitation program in São Paulo, Brazil. Included patients were aged over 18 years, with traumatic unilateral lower-limb amputation, with PLP for at least 3 months after full recovery from amputation surgery. PLP and RLP levels were measured using visual analogue scales. fNIRS was performed during motor execution and motor mirror tasks for 20 s. In order to highlight possible variables related to variation in pain measures, univariate linear regression analyses were performed for both experimental conditions, resulting in four fNIRS variables (two hemispheres x two experimental conditions). Later, in order to test the topographic specificity of the models, eight multivariate regression analyses were performed (two pain scales x two experimental conditions x two hemispheres), including the primary motor cortex (PMC) related channel as an independent variable as well as five other channels related to the premotor area, supplementary area, and somatosensory cortex. All models were controlled for age, sex, ethnicity, and education.

RESULTS

We found that: i) there is an asymmetric metabolic activation during motor execution and mirror task between hemispheres (with a predominance that is ipsilateral to the amputated limb), ii) increased metabolic response in the PMC ipsilateral to the amputation is associated with increased PLP (during both experimental tasks), while increased metabolic response in the contralateral PMC is associated with increased RLP (during the mirror motor task only); ii) increased metabolic activity of the ipsilateral premotor region is associated with increased PLP during the motor mirror task; iii) RLP was only associated with higher metabolic activity in the contralateral PMC and lower metabolic activity in the ipsilateral inferior frontal region during motor mirror task, but PLP was associated with higher metabolic activity during both tasks.

CONCLUSION

These results suggest there is both task and region specificity for the association between the brain metabolic response and the two different types of post-amputation pain. The metabolic predominance that is ipsilateral to the amputated limb during both tasks was associated with higher levels of PLP, suggesting a cortical motor network activity imbalance due to potential interhemispheric compensatory mechanisms. The present work contributes to the understanding of the underlying topographical patterns in the motor-related circuits associated with pain after amputations.

Factors associated with pain pressure threshold in both local and remote sites in knee osteoarthritis

BACKGROUND

Knee osteoarthritis (KOA) is a prevalent condition, and its most frequent symptom is pain that often leads to disability. Pain sensitization is a core feature of KOA, and it can be measured through quantitative sensory testing protocols such as pain pressure threshold (PPT). However, there is a lack of understanding about the factors that may influence changes in PPTs in the KOA population.

OBJECTIVE

To explore the clinical and functional factors associated with PPTs in a sample of people with chronic KOA pain and to compare models of local (knees) and remote (thenar regions) sites.

DESIGN

Cross-sectional analysis of a prospective cohort.

SETTING

Primary care in public institution.

PARTICIPANTS

113 adults with KOA.

INTERVENTION

N/A.

MAIN OUTCOME MEASURES

Multivariable regression analyses evaluating demographic, clinical, and functional variables that could be associated with local and remote PPTs (main outcomes) were performed.

RESULTS

Both thenar region (adjusted-R2 : 0.29) and knee (adjusted-R2 : 0.45) models had the same significant negative association with being a female, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain levels (thenar: β: -0.15, p = .002; knee: β: -0.2, p < .001), and the 10-Meter Walking Test (thenar: β: -0.05, p = .038; knee: β: -0.08, p = .004). A small significant positive association with depressive symptoms was identified in both models, which acted as a confounder for WOMAC pain and was likely affected by unmeasured confounders.

CONCLUSIONS

PPTs in KOA pain are associated with functional outcomes such as the 10-Meter Walking Test and activity-related pain intensity; thus more disability is associated with smaller pain thresholds. Similarity between models may suggest central sensitization.

Intracortical and interhemispheric excitability changes in arm amputees: A TMS study

OBJECTIVE

To evaluate cortical circuits and excitability of the motor cortex in the hemisphere contralateral to the affected (AH) and to the unaffected arm (UH), in upper limb amputees.

METHODS

Motor evoked potentials (MEP) were recorded in 17 subjects who had upper limb amputation: 11 trans-radial (TR) and 6 trans-humeral (TH). Motor thresholds (MT), short interval intracortical inhibition (SICI), and interhemispheric inhibition (IHI) in the available arm muscles of the stump were evaluated.

RESULTS

There was no significant difference in MT between hemispheres. SICI was preserved in TR but not in TH group. Additionally, in the TR group, the MEP amplitudes in AH were higher than in UH. A significant IHI was observed in the whole sample but not in each hemisphere or patient group.

CONCLUSIONS

In our population of TR amputees, we found increased corticospinal excitability in the AH with preserved intracortical inhibition. This finding was not observed in the TH population.

SIGNIFICANCE

Understanding the changes in intracortical excitability in amputees may enhance knowledge of the functional reorganization of the brain in the post-amputation phase, bringing useful information for prosthetic rehabilitation.

The Analgesic Effect of Transcranial Direct Current Stimulation in Fibromyalgia: A Systematic Review, Meta-Analysis, and Meta-Regression of Potential Influencers of Clinical Effect

BACKGROUND

There is tentative evidence to support the analgesic effect of transcranial direct current stimulation (tDCS) in fibromyalgia (FM), with large variability in the effect size (ES) encountered in different clinical trials. Understanding the source of the variability and exploring how it relates to the clinical results could characterize effective neuromodulation protocols and ultimately guide care in FM pain. The primary objective of this study was to determine the effect of tDCS in FM pain as compared with sham tDCS. The secondary objective was to explore the relationship of methodology, population, and intervention factors and the analgesic effect of tDCS in FM.

MATERIALS AND METHODS

For the primary objective, a systematic review was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Randomized clinical trials (RCTs) investigating tDCS as an intervention for FM pain were searched in MEDLINE, Embase, and the Web Of Science. Studies were excluded if they used cross-over designs or if they did not use tDCS as an intervention for pain or did not measure clinical pain. Analysis for the main outcome was performed using a random-effects model. Risk of bias and evidence certainty were assessed for all studies using Cochrane Risk of Bias and Grading of Recommendations Assessment, Development, and Evaluation tools. For the secondary objective, a meta-regression was conducted to explore methodology, population, and intervention factors potentially related to the ES.

RESULTS

Sixteen RCTs were included. Six studies presented a high risk of bias. Significant reduction in pain scores were found for FM (standardized mean difference = 1.22, 95% CI = 0.80-1.65, p < 0.001). Subgroup analysis considering tDCS as a neural target revealed no differences between common neural sites. Meta-regression revealed that the duration of the tDCS protocol in weeks was the only factor associated with the ES, in which protocols that lasted four weeks or longer reported larger ES than shorter protocols.

CONCLUSIONS

Results suggest an analgesic effect of tDCS in FM. tDCS protocols that last four weeks or more may be associated with larger ESs. Definite conclusions are inadequate given the large heterogeneity and limited quality of evidence of the included studies.

Motor Cortex Inhibition and Facilitation Correlates with Fibromyalgia Compensatory Mechanisms and Pain: A Cross-Sectional Study

The role of transcranial magnetic stimulation (TMS) measures as biomarkers of fibromyalgia syndrome (FMS) phenotypes is still unclear. We aimed to determine the clinical correlates of TMS measures in FMS patients. We conducted a cross-sectional analysis that included 58 patients. We performed standardized TMS assessments, including resting motor threshold (MT), motor-evoked potential (MEP), short intracortical inhibition (SICI), and intracortical facilitation (ICF). Sociodemographic, clinical questionnaires, and quantitative sensory testing were collected from all of the patients. Univariate and multivariate linear regression models were built to explore TMS-associated factors. We found that SICI did not significantly correlate with pain levels but was associated with sleepiness, comorbidities, disease duration, and anxiety. On the other hand, ICF showed a positive correlation with pain levels and a negative correlation with body mass index (BMI). BMI was a negative effect modifier of the ICF and pain association. The clinical correlates of MT and MEP were scarce. Our results suggest that SICI and ICF metrics are potential phenotyping biomarkers in FMS related to disease compensation and levels of pain perception, respectively. The clinical translation of TMS paired-pulse protocols represents an opportunity for a mechanistic understanding of FMS and the future development of precision treatments.

Detangling the Structural Neural Correlates Associated with Resting versus Dynamic Phantom Limb Pain Intensity Using a Voxel-based Morphometry Analysis

The management of phantom limb pain (PLP) is still challenging due to a partial understanding of its neurophysiological mechanisms. Structural neuroimaging features are potential biomarkers. However, only a few studies assessed their correlations with clinical severity and treatment response. This study aims to explore the association between brain gray matter volume (GMV) with phantom limb manifestations severity and PLP improvement after neuromodulatory treatments (transcranial direct current stimulation and mirror therapy). Voxel-based morphometry analyses and functional decoding using a reverse inference term-based meta-analytic approach were used. We included 24 lower limb traumatic amputees with moderate to severe PLP. We found that alterations of cortical GMV were correlated with PLP severity but not with other clinical manifestations. Less PLP severity was associated with larger brain clusters GMV in the non-affected prefrontal, insula (non-affected mid-anterior region), and bilateral thalamus. However, only the insula cluster survived adjustments. Moreover, the reverse inference meta-analytic approach revealed that the found insula cluster is highly functionally connected to the contralateral insula and premotor cortices, and the decoded psychological processes related to this cluster were "rating," "sustained attention," "impulsivity, " and "suffering." Moreover, we found that responders to neuromodulatory treatment have higher GMV in somatosensory areas (total volume of S1 and S2) in the affected hemisphere at baseline, compared to non-responders, even after adjustments.

Altered intra- and inter-network brain functional connectivity in upper-limb amputees revealed through independent component analysis

Although cerebral neuroplasticity following amputation has been observed, little is understood about how network-level functional reorganization occurs in the brain following upper-limb amputation. The objective of this study was to analyze alterations in brain network functional connectivity (FC) in upper-limb amputees (ULAs). This observational study included 40 ULAs and 40 healthy control subjects; all participants underwent resting-state functional magnetic resonance imaging. Changes in intra- and inter-network FC in ULAs were quantified using independent component analysis and brain network FC analysis. We also analyzed the correlation between FC and clinical manifestations, such as pain. We identified 11 independent components using independent component analysis from all subjects. In ULAs, intra-network FC was decreased in the left precuneus (precuneus gyrus) within the dorsal attention network and left precentral (precentral gyrus) within the auditory network; but increased in the left Parietal_Inf (inferior parietal, but supramarginal and angular gyri) within the ventral sensorimotor network, right Cerebelum_Crus2 (crus II of cerebellum) and left Temporal_Mid (middle temporal gyrus) within the ventral attention network, and left Rolandic_Oper (rolandic operculum) within the auditory network. ULAs also showed decreased inter-network FCs between the dorsal sensorimotor network and ventral sensorimotor network, the dorsal sensorimotor network and right frontoparietal network, and the dorsal sensorimotor network and dorsal attention network. Correlation analyses revealed negative correlations between inter-network FC changes and residual limb pain and phantom limb pain scores, but positive correlations between inter-network FC changes and daily activity hours of stump limb. These results show that post-amputation plasticity in ULAs is not restricted to local remapping; rather, it also occurs at a network level across several cortical regions. This observation provides additional insights into the plasticity of brain networks after upper-limb amputation, and could contribute to identification of the mechanisms underlying post-amputation pain.

[Randomized Controlled Trial of the Effects of Repetitive Transcranial Magnetic Stimulation and Mirror Therapy on Phantom Limb Pain in Amputees]

Objective

To investigate the effect of repetitive transcranial magnetic stimulation (rTMS) on phantom limb pain (PLP) in amputees, and to compare the therapeutic effect with that of mirror therapy (MT).

Methods

The study was designed as a randomized controlled trial. The evaluators were blinded, while the subjects and the therapists were unblinded. Subjects were randomly assigned to either the rTMS group or the MT group with a computer-generated random number table. From June 2018 to December 2020, from out of 45 amputee patients screened for the study, 30 who met the inclusion criteria were recruited for the study. All patients were recruited from the Rehabilitation Medicine Center, West China Hospital, Sichuan University. In the end, 4 patients withdrew from the study and 26 patients (12 in the rTMS group and 14 in the MT group) completed the prescribed treatment and evaluation. The rTMS group was given rTMS (1 Hz, 15 min, 5 d/week) for 2 weeks in addition to conventional rehabilitation therapy, while the MT group received MT (corresponding movements of limbs, 15 min, 5 d/week) for 2 weeks in addition to conventional rehabilitation therapy. PLP was evaluated by the Visual Analogue Scale (VAS) and Douleur Neuropathique 4 Questions (DN-4). Subjects were assessed before treatment ( t 0), immediately after the completion of the treatment ( t 1) and 3 months after the completion of the treatment ( t 2).

Results

The mean age of the 26 patients was 39.73±12.64. There were 15 males and 11 females. According to the reported description of the characteristics of the PLP by the patients, the characteristics with the highest incidence were tingling, stabbing, numbing, electric shocks and burning in descending order. There was no significant difference in the incidence of PLP characteristics between the two groups ( P>0.05). The two groups had comparable baseline data, showing no significant difference in VAS and DN-4 between the two groups at t 0 ( P>0.05). At t 1 and t 2, the VAS and DN-4 scores were decreased from those of t 0, showing statistically significant difference in both groups ( P<0.01 for both scores). In the rTMS group, there was no significant difference between VAS and DN-4 scores at t 1 and those at t 2 ( P>0.05). In the MT group, the VAS and DN-4 scores at t 2 were significantly lower than those of t 1 ( P<0.05). There was no statistically significant difference between the rTMS group and MT group in the changes in pain measurements, i.e., VAS and DN-4 scores, before and after the intervention ( P>0.05). The 26 patients who completed the experiment showed no dizziness, headache, or other abnormalities during the study.

Conclusion

The results of this study indicate that repetitive transcranial magnetic stimulation could improve PLP in amputees, and the improvement effect was comparable to that of mirror therapy.

Motor cortex inhibition as a fibromyalgia biomarker: a meta-analysis of transcranial magnetic stimulation studies

Fibromyalgia (FM) is a common and refractory chronic pain condition with multiple clinical phenotypes. The current diagnosis is based on a syndrome identification which can be subjective and lead to under or over-diagnosis. Therefore, there is a need for objective biomarkers for diagnosis, phenotyping, and prognosis (treatment response and follow-up) in fibromyalgia. Potential biomarkers are measures of cortical excitability indexed by transcranial magnetic stimulation (TMS). However, no systematic analysis of current evidence has been performed to assess the role of TMS metrics as a fibromyalgia biomarker. Therefore, this study aims to evaluate evidence on corticospinal and intracortical motor excitability in fibromyalgia subjects and to assess the prognostic role of TMS metrics as response biomarkers in FM. We conducted systematic searches on PubMed/Medline, Embase, and Cochrane Central databases for observational studies and randomized controlled trials on fibromyalgia subjects that used TMS as an assessment. Three reviewers independently selected and extracted the data. Then, a random-effects model meta-analysis was performed to compare fibromyalgia and healthy controls in observational studies. Also, to compare active versus sham treatments, in randomized controlled trials. Correlations between changes in TMS metrics and clinical improvement were explored. The quality and evidence certainty were assessed following standardized approaches. We included 15 studies (696 participants, 474 FM subjects). The main findings were: (1) fibromyalgia subjects present less intracortical inhibition (mean difference (MD) = -0.40, 95% confidence interval (CI) -0.69 to -0.11) and higher resting motor thresholds (MD = 6.90 μV, 95% CI 4.16 to 9.63 μV) when compared to controls; (2) interventions such as exercise, pregabalin, and non-invasive brain stimulation increased intracortical inhibition (MD = 0.19, 95% CI 0.10 to 0.29) and cortical silent period (MD = 14.92 ms, 95% CI 4.86 to 24.98 ms), when compared to placebo or sham stimulation; (3) changes on intracortical excitability are correlated with clinical improvements - higher inhibition moderately correlates with less pain, depression, and pain catastrophizing; lower facilitation moderately correlates with less fatigue. Measures of intracortical inhibition and facilitation indexed by TMS are potential diagnostic and treatment response biomarkers for fibromyalgia subjects. The disruption in the intracortical inhibitory system in fibromyalgia also provides additional evidence that fibromyalgia has some neurophysiological characteristics of neuropathic pain. Treatments inducing an engagement of sensorimotor systems (e.g., exercise, motor imagery, and non-invasive brain stimulation) could restore the cortical inhibitory tonus in FM and induce clinical improvement.

Cortical stimulation for chronic pain: from anecdote to evidence

Epidural stimulation of the motor cortex (eMCS) was devised in the 1990's, and has now largely supplanted thalamic stimulation for neuropathic pain relief. Its mechanisms of action involve activation of multiple cortico-subcortical areas initiated in the thalamus, with involvement of endogenous opioids and descending inhibition toward the spinal cord. Evidence for clinical efficacy is now supported by at least seven RCTs; benefits may persist up to 10 years, and can be reasonably predicted by preoperative use of non-invasive repetitive magnetic stimulation (rTMS). rTMS first developed as a means of predicting the efficacy of epidural procedures, then as an analgesic method on its own right. Reasonable evidence from at least six well-conducted RCTs favors a significant analgesic effect of high-frequency rTMS of the motor cortex in neuropathic pain (NP), and less consistently in widespread/fibromyalgic pain. Stimulation of the dorsolateral frontal cortex (DLPFC) has not proven efficacious for pain, so far. The posterior operculo-insular cortex is a new and attractive target but evidence remains inconsistent. Transcranial direct current stimulation (tDCS) is applied upon similar targets as rTMS and eMCS; it does not elicit action potentials but modulates the neuronal resting membrane state. tDCS presents practical advantages including low cost, few safety issues, and possibility of home-based protocols; however, the limited quality of most published reports entails a low level of evidence. Patients responsive to tDCS may differ from those improved by rTMS, and in both cases repeated sessions over a long time may be required to achieve clinically significant relief. Both invasive and non-invasive procedures exert their effects through multiple distributed brain networks influencing the sensory, affective and cognitive aspects of chronic pain. Their effects are mainly exerted upon abnormally sensitized pathways, rather than on acute physiological pain. Extending the duration of long-term benefits remains a challenge, for which different strategies are discussed in this review.

Structural and Functional Asymmetry in Precentral and Postcentral Gyrus in Patients With Unilateral Chronic Shoulder Pain

OBJECTIVE

The purpose of this study was to explore the structural and functional asymmetry of precentral and postcentral gyrus in patients with unilateral chronic shoulder pain (CSP) utilizing MRI.

PATIENTS AND METHODS

We collected structural and resting-state functional MRI (rs-fMRI) data in 22 left-sided, 15 patients with right-sided CSP, and 24 healthy controls (HCs). Here, we performed the structural asymmetry and seed-based functional connectivity (FC) analyses. We extracted regional cortical thickness and surface area measurements from T1-weighted MRI images, using asymmetry indexes (AIs) to assess asymmetries. We used Data Processing and Analysis for Brain Imaging software for seed-based FC analysis and selected unilateral-precentral and postcentral as the regions of interest. Then, we performed group comparisons of the neuroimaging metrics, and also explored the relationships between brain asymmetry and clinical variables.

RESULTS

We found significant differences in surface area AIs of the precentral among three groups, the AI values were negatively correlated with the visual analog scale score and positively correlated with Constant-Murley scores (CMS) in the left-sided CSP group. Further, FC of left postcentral with cingulate gyrus and left paracentral lobule showed significant group differences; FC of right postcentral with left caudate, left paracentral, and left postcentral were different among groups; FC of right precentral with the cingulate gyrus, precuneus, and left paracentral revealed significant group differences. Besides, there was a positive correlation between right precentral-cingulate gyrus FC and CMS in the right-sided CSP group.

CONCLUSION

Surface area and FC patterns asymmetry exist in precentral and postcentral gyrus in patients with unilateral CSP. Asymmetry trend is associated with pain severity and shoulder joint function impairment. Brain structural and functional asymmetry may be an important indicator for understanding the potential mechanism of chronic pain.

Glutamatergic System in Depression and Its Role in Neuromodulatory Techniques Optimization

Depressive disorders are among the most common psychiatric conditions and contribute to significant morbidity. Even though the use of antidepressants revolutionized the management of depression and had a tremendous positive impact on the patient's outcome, a significant proportion of patients with major depressive disorder (MDD) show no or partial or response even with adequate treatment. Given the limitations of the prevailing monoamine hypothesis-based pharmacotherapy, glutamate and glutamatergic related pathways may offer an alternative and a complementary option for designing novel intervention strategies. Over the past few decades, there has been a growing interest in understanding the neurobiological underpinnings of glutamatergic dysfunctions in the pathogenesis of depressive disorders and the development of new pharmacological and non-pharmacological treatment options. There is a growing body of evidence for the efficacy of neuromodulation techniques, including transcranial magnetic stimulation, transcutaneous direct current stimulation, transcranial alternating current stimulation, and photo-biomodulation on improving connectivity and neuroplasticity associated with depression. This review attempts to revisit the role of glutamatergic neurotransmission in the etiopathogenesis of depressive disorders and review the current neuroimaging, neurophysiological and clinical evidence of these neuromodulation techniques in the pathophysiology and treatment of depression.

Home-based transcranial direct current stimulation (tDCS) and motor imagery for phantom limb pain using statistical learning to predict treatment response: an open-label study protocol

Background

Phantom limb pain (PLP) management has been a challenge due to its response heterogeneity and lack of treatment access. This study will evaluate the feasibility of a remotely home-based M1 anodal tDCS combined with motor imagery in phantom limb patients and assess the preliminary efficacy, safety, and predictors of response of this therapy.

Methods

This is a pilot, single-arm, open-label trial in which we will recruit 10 subjects with phantom limb pain. The study will include 20 sessions. All participants will receive active anodal M1 tDCS combined with phantom limb motor imagery training. Our primary outcome will be the acceptability and feasibility of this combined intervention. Moreover, we will assess preliminary clinical (pain intensity) and physiological (motor inhibition tasks and heart rate variability) changes after treatment. Finally, we will implement a supervised statistical learning (SL) model to identify predictors of treatment response (to tDCS and phantom limb motor imagery) in PLP patients. We will also use data from our previous clinical trial (total observations=224 [n=112 x timepoints = 2)) for our statistical learning algorithms. The new prospective data from this open-label study will be used as an independent test dataset.

Discussion

This protocol proposes to assess the feasibility of a novel, neuromodulatory combined intervention that will allow the design of larger remote clinical trials, thus increasing access to safe and effective treatments for PLP patients. Moreover, this study will allow us to identify possible predictors of pain response and PLP clinical endotypes.

Increased motor cortex inhibition as a marker of compensation to chronic pain in knee osteoarthritis

This study aims to investigate the associative and multivariate relationship between different sociodemographic and clinical variables with cortical excitability as indexed by transcranial magnetic stimulation (TMS) markers in subjects with chronic pain caused by knee osteoarthritis (OA). This was a cross-sectional study. Sociodemographic and clinical data were extracted from 107 knee OA subjects. To identify associated factors, we performed independent univariate and multivariate regression models per TMS markers: motor threshold (MT), motor evoked potential (MEP), short intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP). In our multivariate models, the two markers of intracortical inhibition, SICI and CSP, had a similar signature. SICI was associated with age (β: 0.01), WOMAC pain (β: 0.023), OA severity (as indexed by Kellgren–Lawrence Classification) (β: − 0.07), and anxiety (β: − 0.015). Similarly, CSP was associated with age (β: − 0.929), OA severity (β: 6.755), and cognition (as indexed by the Montreal Cognitive Assessment) (β: − 2.106). ICF and MT showed distinct signatures from SICI and CSP. ICF was associated with pain measured through the Visual Analogue Scale (β: − 0.094) and WOMAC (β: 0.062), and anxiety (β: − 0.039). Likewise, MT was associated with WOMAC (β: 1.029) and VAS (β: − 2.003) pain scales, anxiety (β: − 0.813), and age (β: − 0.306). These associations showed the fundamental role of intracortical inhibition as a marker of adaptation to chronic pain. Subjects with higher intracortical inhibition (likely subjects with more compensation) are younger, have greater cartilage degeneration (as seen by radiographic severity), and have less pain in WOMAC scale. While it does seem that ICF and MT may indicate a more acute marker of adaptation, such as that higher ICF and MT in the motor cortex is associated with lesser pain and anxiety.

Effects of Combined and Alone Transcranial Motor Cortex Stimulation and Mirror Therapy in Phantom Limb Pain: A Randomized Factorial Trial

Phantom limb pain (PLP) is a frequent complication in amputees, which is often refractory to treatments. We aim to assess in a factorial trial the effects of transcranial direct current stimulation (tDCS) and mirror therapy (MT) in patients with traumatic lower limb amputation; and whether the motor cortex plasticity changes drive these results. In this large randomized, blinded, 2-site, sham-controlled, 2 × 2 factorial trial, 112 participants with traumatic lower limb amputation were randomized into treatment groups. The interventions were active or covered MT for 4 weeks (20 sessions, 15 minutes each) combined with 2 weeks of either active or sham tDCS (10 sessions, 20 minutes each) applied to the contralateral primary motor cortex. The primary outcome was PLP changes on the visual analogue scale at the end of interventions (4 weeks). Motor cortex excitability and cortical mapping were assessed by transcranial magnetic stimulation (TMS). We found no interaction between tDCS and MT groups (F = 1.90, P = .13). In the adjusted models, there was a main effect of active tDCS compared to sham tDCS (beta coefficient = -0.99, P = .04) on phantom pain. The overall effect size was 1.19 (95% confidence interval: 0.90, 1.47). No changes in depression and anxiety were found. TDCS intervention was associated with increased intracortical inhibition (coefficient = 0.96, P = .02) and facilitation (coefficient = 2.03, P = .03) as well as a posterolateral shift of the center of gravity in the affected hemisphere. MT induced no motor cortex plasticity changes assessed by TMS. These findings indicate that transcranial motor cortex stimulation might be an affordable and beneficial PLP treatment modality.

Understanding intracortical excitability in phantom limb pain: A multivariate analysis from a multicenter randomized clinical trial

OBJECTIVES

To explore associations of intracortical excitability with clinical characteristics in a large sample of subjects with phantom limb pain (PLP).

METHODS

Ancillary study using baseline and longitudinal data from a large multicenter randomized trial that investigated the effects of non-invasive brain stimulation combined with sensorimotor training on PLP. Multivariate regression modeling analyses were used to investigate the association of intracortical excitability, measured by percentages of intracortical inhibition (ICI) and facilitation (ICF) with clinical variables.

RESULTS

Ninety-eight subjects were included. Phantom sensation of itching was positively associated with ICI changes and at baseline in the affected hemisphere (contralateral to PLP). However, in the non-affected hemisphere (ipsilateral to PLP), the phantom sensation of warmth and PLP intensity were negatively associated with ICI (both models). For the ICF, PLP intensity (baseline model only) and age (longitudinal model) were negatively associated, while time since amputation and amputation level (both for longitudinal model only) were positively associated in the affected hemisphere. Additionally, use of antidepressants led to lower ICF in the non-affected hemisphere for the baseline model while higher amputation level also led to less changes in the ICF.

CONCLUSION

Results revealed clear associations of clinical variables and cortical excitability in a large chronic pain sample. ICI and ICF changes appear not to be mainly explained by PLP intensity. Instead, other variables associated with duration of neuroplasticity changes (such as age and duration of amputation) and compensatory mechanisms (such as itching and phantom limb sensation) seem to be more important in explaining these variables.

Community ambulation in people with lower limb amputation: An observational cohort study

ABSTRACT

Lower limb amputation (LLA) is still a health issue requiring rehabilitation and long-term care even in industrial societies. Several studies on subjects with LLA have been focused on the efficacy of rehabilitation and factors influencing the use of prosthesis. However, literature data on the recovery of ability to walk outdoors, and thus to participate in social life in this population is limited.To investigate potential correlations between socio-demographic and clinical factors, and the use of the prosthesis for indoor and/or outdoor walking referred to as community ambulation (CA) in subjects with LLA.An observational cohort study on 687 LLA subjects was conducted. Socio-demographic and clinical characteristics of 302 subjects who received similar rehabilitative treatment with respect to the standard protocol were collected by a telephone survey with a structured questionnaire. The CA recovery, in terms of patient's autonomy and participation, assessed by Walking Handicap Scale, was considered as the main outcome.The univariate analysis demonstrated statistical significant positive correlation between CA and gender (χ2 = 3.901, P = .048); amputation level (χ2 = 24.657, P < .001); pre-LLA (χ2 = 6.338, P = .012) and current work activity (χ2 = 25.192, P < .001); prosthesis use (χ2 = 187.037, P < .01); and time from LLA (r = 0.183, P < .001); increasing age was negatively correlated with the outcome (r = -0.329, P < .001), while pain intensity was not significant. Being male (75.4%); trans-tibial (TT) amputation level (9.79%); working before (3.81%) and after LLA (7.68%); and the prosthesis use (24.63%) increased the probability of CA recovery. Multivariate binary logistic regression analysis confirmed that the prosthesis use (P < .001) and TT amputation level (P = .042) are predictors of a positive outcome (Walking Handicap Scale 4-6).These findings highlight the importance of the use of prosthesis in people with LLA for the restoration of a good capacity of participation (CA), especially in subjects with TT amputation level. The identification of predictive factors may help tailor-made rehabilitation approaches addressing an earlier reintegration to social life.