Phantom limb pain: a case of maladaptive CNS plasticity?

Acute versus non-acute targeted muscle reinnervation for pain control following major limb amputation: A comparative study

BACKGROUND

Targeted muscle reinnervation (TMR) has been shown to reduce phantom limb pain (PLP) and residual limb pain (RLP) after major limb amputation. However, the effect of the timing of surgery on pain control and quality of life outcomes is controversial. We conducted a retrospective study to compare the outcomes of acute TMR for pain prevention with non-acute TMR for the treatment of established pain.

METHODS

All patients treated with TMR in our institution between January 2018 and December 2021 were evaluated at 6, 12, 18 and 24 months post-operatively. Pain intensity and quality of life outcomes were assessed using the Brief Pain Inventory (Pain Severity and Pain Interference scales) and Pain Catastrophizing Scale. Outcomes were compared between acute and non-acute TMR using the Wilcoxon ranked-sum test or Fisher's exact test as appropriate. Multilevel mixed-effects linear regression was used to account for repeat measures and potential pain confounders.

RESULTS

Thirty-two patients with 38 major limb amputations were included. Acute TMR patients reported significantly lower RLP and PLP scores, pain interference and pain catastrophisation at all time points (p < 0.05). Acute TMR was significantly associated with lower pain severity and pain interference in a linear mixed-effects model accounting for patient age, gender, amputation indication, amputation site, time post-TMR and repeated surveys (p < 0.05). There was no significant difference in the complication rate (p = 0.51).

CONCLUSION

Acute TMR was associated with clinically and statistically significant pain outcomes that were better than that in non-acute TMR. This suggests that TMR should be performed with preventative intent, when possible, as part of a multidisciplinary approach to pain management, rather than deferred until the development of chronic pain.

Resting state neurophysiology of agonist-antagonist myoneural interface in persons with transtibial amputation

The agonist-antagonist myoneural interface (AMI) is an amputation surgery that preserves sensorimotor signaling mechanisms of the central-peripheral nervous systems. Our first neuroimaging study investigating AMI subjects conducted by Srinivasan et al. (2020) focused on task-based neural signatures, and showed evidence of proprioceptive feedback to the central nervous system. The study of resting state neural activity helps non-invasively characterize the neural patterns that prime task response. In this study on resting state functional magnetic resonance imaging in AMI subjects, we compared functional connectivity in patients with transtibial AMI (n = 12) and traditional (n = 7) amputations (TA). To test our hypothesis that we would find significant neurophysiological differences between AMI and TA subjects, we performed a whole-brain exploratory analysis to identify a seed region; namely, we conducted ANOVA, followed by t-test statistics to locate a seed in the salience network. Then, we implemented a seed-based connectivity analysis to gather cluster-level inferences contrasting our subject groups. We show evidence supporting our hypothesis that the AMI surgery induces functional network reorganization resulting in a neural configuration that significantly differs from the neural configuration after TA surgery. AMI subjects show significantly less coupling with regions functionally dedicated to selecting where to focus attention when it comes to salient stimuli. Our findings provide researchers and clinicians with a critical mechanistic understanding of the effect of AMI amputation on brain networks at rest, which has promising implications for improved neurorehabilitation and prosthetic control.

Phantom limb syndrome: from pathogenesis to treatment. A narrative review

Phantom Limb Syndrome (PLS) can be defined as the disabling or painful sensation of the presence of a body part that is no longer present after its amputation. Anatomical changes involved in Phantom Limb Syndrome, occurring at peripheral, spinal and brain levels and include the formation of neuromas and scars, dorsal horn sensitization and plasticity, short-term and long-term modifications at molecular and topographical levels. The molecular reorganization processes of Phantom Limb Syndrome include NMDA receptors hyperactivation in the dorsal horn of the spinal column leading to inflammatory mechanisms both at a peripheral and central level. At the brain level, a central role has been recognized for sodium channels, BDNF and adenosine triphosphate receptors. In the paper we discuss current available pharmacological options with a final overview on non-pharmacological options in the pipeline.

Primary 3-Month Outcomes of a Double-Blind Randomized Prospective Study (The QUEST Study) Assessing Effectiveness and Safety of Novel High-Frequency Electric Nerve Block System for Treatment of Post-Amputation Pain

Purpose

This multicenter, randomized, double-blinded, active sham-controlled pivotal study was designed to assess the efficacy and safety of high-frequency nerve block treatment for chronic post-amputation and phantom limb pain.

Patients and Methods

QUEST enrolled 180 unilateral lower-limb amputees with severe post-amputation pain, 170 of whom were implanted with the Altius device, were randomized 1:1 to active-sham or treatment groups and reached the primary endpoint. Responders were those subjects who received ≥50% pain relief 30 min after treatment in ≥50% of their self-initiated treatment sessions within the 3-month randomized period. Differences between the active treatment and sham control groups as well as numerous secondary outcomes were determined.

Results

At 30-min, (primary outcome), 24.7% of the treatment group were responders compared to 7.1% of the control group (p=0.002). At 120-minutes following treatment, responder rates were 46.8% in the Treatment group and 22.2% in the Control group (p=0.001). Improvement in Brief Pain Inventory interference score of 2.3 ± 0.29 was significantly greater in treatment group than the 1.3 ± 0.26-point change in the Control group (p = 0.01). Opioid usage, although not significantly different, trended towards a greater reduction in the treatment group than in the control group. The incidence of adverse events did not differ significantly between the treatment and control groups.

Conclusion

The primary outcomes of the study were met, and the majority of Treatment patients experienced a substantial improvement in PAP (regardless of meeting the study definition of a responder). The significant in PAP was associated with significantly improved QOL metrics, and a trend towards reduced opioid utilization compared to Control. These data indicate that Altius treatment represents a significant therapeutic advancement for lower-limb amputees suffering from chronic PAP.

Targeted Muscle Reinnervation: Factors Predisposing to Successful Pain Score Reduction

BACKGROUND

Targeted muscle reinnervation (TMR) has demonstrated efficacy in reducing neuroma and chronic pain. In this article, we investigated postoperative outcomes in our patient cohort, with a focus on the role of nonmodifiable factors such as patient age and gender.

METHODS

Patients who had extremity TMR from April 2018 to October 2022 were reviewed. Outcomes of interest included patient age, gender, cause and type of amputation, delayed versus immediate TMR, as well as postoperative improvement in pain as assessed by numerical rating score (NRS).

RESULTS

A total of 40 patients underwent TMR on 47 limbs. Mean age was 46.2 ± 17.0 years. Delayed TMR (27, 57.4%) was most commonly performed, followed by immediate and delayed-immediate at 11 (23.4%) and 9 (19.1%), respectively. Amputation level was most commonly above-knee in 20 (42.6%) patients, followed by below-knee (12, 25.5%), transhumeral (8, 17.0%), transradial (6, 12.8%), and shoulder (1, 2.1%). The median time interval between amputation and TMR was 12 months. The median preoperative NRS assessing residual limb pain (RLP) for patients who underwent delayed TMR was 10. The median postoperative NRS assessing RLP for all patients was 0 (interquartile range25-75: 0-5) and significantly improved compared with preoperative NRS (P < 0.001). At the last follow-up for limbs that had delayed and delayed-immediate TMR (n = 36), 33 (91.7%) limbs had more than 50% resolution of RLP. There was a significant difference in median postoperative NRS by gender (4 in men and 0 in women) (P < 0.05). Postoperative median NRS also favored younger patients (0, <50 years compared with 4.5, >50 years) (P < 0.05). Multiple linear regression analysis showed that, of different variables analyzed, only male gender and older age were predictive of poorer postoperative outcomes.

CONCLUSION

TMR showed high efficacy in our cohort, with improved short-term outcomes in women and younger patients.

A new perspective on positive symptoms: expression of damage or self-defence mechanism of the brain?

Usually, positive neurological symptoms are considered as the consequence of a mere, afinalistic and abnormal increase in function of specific brain areas. However, according to the Theory of Active Inference, which argues that action and perception constitute a loop that updates expectations according to a Bayesian model, the brain is rather an explorer that formulates hypotheses and tests them to assess the correspondence between internal models and reality. Moreover, the cerebral cortex is characterised by a continuous "conflict" between different brain areas, which constantly attempt to expand in order to acquire more of the limited available computational resources, by means of their dopamine-induced neuroplasticity. Thus, it has recently been suggested that dreams, during rapid eye movement sleep (REMS), protect visual brain areas (deprived of their stimuli during rest) from being conquered by other normally stimulated ones. It is therefore conceivable that positive symptoms also have a functional importance for the brain. We evaluate supporting literature data of a 'defensive' role of positive symptoms and the relevance of dopamine-induced neuroplasticity in the context of neurodegenerative and psychiatric diseases. Furthermore, the possible functional significance of idiopathic REMS-related behavioural disorder as well as phantom limb syndrome is examined. We suggest that positive neurological symptoms are not merely a passive expression of a damage, but active efforts, related to dopamine-induced plasticity, to maintain a correct relationship between the external world and its brain representation, thus preventing healthy cortical areas from ousting injured ones.

Can the neural representation of physical pain predict empathy for pain in others?

The question of whether physical pain and vicarious pain have some shared neural substrates is unresolved. Recent research has argued that physical and vicarious pain are represented by dissociable multivariate brain patterns by creating biomarkers for physical pain (Neurologic Pain Signature, NPS) and vicarious pain (Vicarious Pain Signature, VPS), respectively. In the current research, the NPS and two versions of the VPS were applied to three fMRI datasets (one new, two published) relating to vicarious pain which focused on between-subject differences in vicarious pain (Datasets 1 and 3) and within-subject manipulations of perspective taking (Dataset 2). Results show that (i) NPS can distinguish brain responses to images of pain vs no-pain and to a greater extent in vicarious pain responders who report experiencing pain when observing pain and (ii) neither version of the VPS mapped on to individual differences in vicarious pain and the two versions differed in their success in predicting vicarious pain overall. This study suggests that the NPS (created to detect physical pain) is, under some circumstances, sensitive to vicarious pain and there is significant variability in VPS measures (created to detect vicarious pain) to act as generalizable biomarkers of vicarious pain.

A systematic review of the prevalence of postamputation and chronic neuropathic pain associated with combat injury in military personnel

ABSTRACT

Combat trauma can lead to widespread tissue damage and limb loss. This may result in chronic neuropathic and post amputation pain, including phantom limb pain (PLP) and residual limb pain (RLP). The military population is distinct with respect to demographic, injury, and social characteristics compared with other amputation and trauma cohorts. We undertook a systematic review of studies of military personnel, with a history of combat injury, that reported a prevalence of any type of postamputation pain or chronic neuropathic pain, identified from Embase and MEDLINE databases.Using the inverse variance method with a random-effects model, we undertook a meta-analysis to determine an overall prevalence and performed exploratory analyses to identify the effect of the type of pain, conflict, and time since injury on prevalence. Pain definitions and types of pain measurement tools used in studies were recorded. Thirty-one studies (14,738 participants) were included. The pooled prevalence of PLP, RLP, and chronic neuropathic pain were 57% (95% CI: 46-68), 61% (95% CI: 50-71), and 26% (95% CI: 10-54), respectively. Between-study heterogeneity was high (I 2 : 94%-98%). Characterisation of duration, frequency, and impact of pain was limited. Factors reported by included studies as being associated with PLP included the presence of RLP and psychological comorbidity. The prevalence of postamputation pain and chronic neuropathic pain after combat trauma is high. We highlight inconsistency of case definitions and terminology for pain and the need for consensus in future research of traumatic injury.

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.

Botulinum toxin therapy for management of phantom and residual limb pain following amputation: A systematic review

Chronic pain following amputation is debilitating. Due to its mechanisms in modulating muscle contraction and pain, botulinum toxin has been investigated as a treatment option for phantom limb pain (PLP) and residual limb pain (RLP). The objective of this study was to determine the efficacy of botulinum toxin injection in the management of PLP and RLP following major limb amputation using a systematic review of the literature. The databases Medline, CINAHL, EMBASE, Scopus, Web of Science, and Cochrane were searched from inception through October 30, 2023. The search identified 50 articles; 37 underwent full-text review, and 11 were included in the final review. Eighty-nine individuals with pain were investigated by the included studies; 53 had RLP and 63 had PLP. There was significant variation in botulinum toxin type, injection method, and dosage. Twenty-one (53.9%) and 27 (64.3%) participants had improvement in PLP and RLP following botulinum toxin injection, respectively. Therefore, there is potential for use of botulinum toxin for the treatment of PLP and RLP. However, due to the minimal number of studies, small sample sizes, and heterogenous methodologies, our ability to conclude with certainty the efficacy of botulinum toxin injection on the treatment of PLP and RLP following amputation is limited.

Is Phantom Limb Awareness Necessary for the Treatment of Phantom Limb Pain?

Phantom limb pain is attributed to abnormal sensorimotor cortical representations. Various feedback treatments have been applied to induce the reorganization of the sensorimotor cortical representations to reduce pain. We developed a training protocol using a brain-computer interface (BCI) to induce plastic changes in the sensorimotor cortical representation of phantom hand movements and demonstrated that BCI training effectively reduces phantom limb pain. By comparing the induced cortical representation and pain, the mechanisms worsening the pain have been attributed to the residual phantom hand representation. Based on our data obtained using neurofeedback training without explicit phantom hand movements and hand-like visual feedback, we suggest a direct relationship between cortical representation and pain. In this review, we summarize the results of our BCI training protocol and discuss the relationship between cortical representation and phantom limb pain. We propose a treatment for phantom limb pain based on real-time neuroimaging to induce appropriate cortical reorganization by monitoring cortical activities.

Mesenchymal Stem Cell Engagement Modulates Neuroma Microenviroment in Rats and Humans and Prevents Postamputation Pain

Postamputation pain is currently managed unsatisfactorily with neuron-targeted pharmacological and interventional therapies. Non-neuronal pain mechanisms have emerged as crucial factors in the development and persistence of postamputation pain. Consequently, these mechanisms offer exciting prospects as innovative therapeutic targets. We examined the hypothesis that engaging mesenchymal stem cells (MSCs) would foster local neuroimmune interactions, leading to a potential reduction in postamputation pain. We utilized an ex vivo neuroma model from a phantom limb pain patient to uncover that the oligodeoxynucleotide IMT504 engaged human primary MSCs to promote an anti-inflammatory microenvironment. Reverse translation experiments recapitulated these effects. Thus, in an in vivo rat model, IMT504 exhibited strong efficacy in preventing autotomy (self-mutilation) behaviors. This effect was linked to a substantial accumulation of MSCs in the neuroma and associated dorsal root ganglia and the establishment of an anti-inflammatory phenotype in these compartments. Centrally, this intervention reduced glial reactivity in the dorsal horn spinal cord, demonstrating diminished nociceptive activity. Accordingly, the exogenous systemic administration of MSCs phenocopied the behavioral effects of IMT504. Our findings underscore the mechanistic relevance of MSCs and the translational therapeutic potential of IMT504 to engage non-neuronal cells for the prevention of postamputation pain. PERSPECTIVE: The present study suggests that IMT504-dependent recruitment of endogenous MSCs within severely injured nerves may prevent post-amputation pain by modifying the inflammatory scenario at relevant sites in the pain pathway. Reinforcing data in rat and human tissues supports the potential therapeutic value of IMT504 in patients suffering postamputation pain.

Prevalence, temporal course and risk factors for phantom eye symptoms in uveal melanoma

BACKGROUND

Phantom eye symptoms (PES), particularly phantom visual sensations (PVS) and phantom eye pain (PEP), are common in enucleated patients and can lead to psychological distress. Current cross-sectional studies cannot examine the temporal course of symptoms, nor can they identify dynamic risk factors or consequences of PES.

METHODS

Cohort study of 105 enucleated uveal melanoma patients returning self-report questionnaires, within 4 weeks of diagnosis and 6-, 12- and 24-months post-treatment. Questionnaires measuring PVS and PEP symptoms in the week prior to completion, pain severity, Hospital Anxiety and Depression Scale scores and the Functional Assessment of Cancer Therapy scale (FACT-G) measuring quality of life.

RESULTS

PVS and PEP emerged after 6 months, were relatively stable over the study and did not remit. PVS showed 6-, 12- and 24-month prevalence rates of 44.6%, 48.2% and 30.2%, and PEP 16.1%, 18.4% and 17.5% respectively. PVS were generally elementary, with only 10-15% of the total cohort experiencing complex sensations. PEP was generally neither prolonged nor intense, except in a small proportion. PVS and PEP were showed moderate associations but did not predict each other prospectively. Anxiety within 4 weeks of diagnosis was a risk factor for the initiation of PEP. Neither PVS nor PEP prospectively predicted anxiety, depression or quality of life.

CONCLUSIONS

PES were prevalent and non-remitting, beginning within 6 months of enucleation. PVS and PEP may not represent symptoms of a coherent syndrome. We discuss findings with reference to theories of phantom sensations, and directions for clinical practise and research.

Effect of Adding Virtual Reality Training to Traditional Exercise Program on Pain, Mental Status and Psychological Status in Unilateral Traumatic Lower Limb Amputees: A Randomized Controlled Trial

Background: Lower limb amputation is an emotionally devastating condition that causes a complete change in the quality of life, may lead to phantom limb pain in most of the cases, and puts the individual in a high risk of developing psychological disorders. The objective of this study is to evaluate the consequence of adding virtual reality (VR) to a traditional exercise program on pain, mental status, and psychological status in traumatic unilateral lower limb amputees (LLAs). Methods: Thirty-two traumatic LLAs were randomly assigned into two equal groups in this randomized control trial. Participants did accomplish a postfitting exercise program at least 6 months before enrolment; the control group (CG) underwent a traditional rehabilitation program, and experimental group (EG) had the same program, in addition to VR training. Data were collected before and after 6 weeks of intervention using visual analog scale (VAS) for pain, Beck's depression inventory (BDI) for depression, and 12-item short form survey for mental health summary (MHS) and physical health summary (PHS). Results: Thirty-two amputees (29 males and 3 females) were included with mean age in CGs and EG (27.6 ± 4) and (27.6 ± 7.6) years, respectively. Postintervention, the VAS score was significantly reduced only in EG (P = 0.003). Both groups showed significant improvement in BDI, MHS, and PHS (P < 0.05). However, the EG showed a superior significance in BDI and MHS scores (P < 0.05). There was no significance between groups in PHS score. Conclusion: Adding VR to conventional training is beneficial in decreasing pain and in improving depression and MHS of traumatic unilateral LLAs.

Approaches to neuropathic amputation-related pain: narrative review of surgical, interventional, and medical treatments

BACKGROUND/IMPORTANCE

Neuropathic amputation-related pain can consist of phantom limb pain (PLP), residual limb pain (RLP), or a combination of both pathologies. Estimated of lifetime prevalence of pain and after amputation ranges between 8% and 72%.

OBJECTIVE

This narrative review aims to summarize the surgical and non-surgical treatment options for amputation-related neuropathic pain to aid in developing optimized multidisciplinary and multimodal treatment plans that leverage multidisciplinary care.

EVIDENCE REVIEW

A search of the English literature using the following keywords was performed: PLP, amputation pain, RLP. Abstract and full-text articles were evaluated for surgical treatments, medical management, regional anesthesia, peripheral block, neuromodulation, spinal cord stimulation, dorsal root ganglia, and peripheral nerve stimulation.

FINDINGS

The evidence supporting most if not all interventions for PLP are inconclusive and lack high certainty. Targeted muscle reinnervation and regional peripheral nerve interface are the leading surgical treatment options for reducing neuroma formation and reducing PLP. Non-surgical options include pharmaceutical therapy, regional interventional techniques and behavioral therapies that can benefit certain patients. There is a growing evidence that neuromodulation at the spinal cord or the dorsal root ganglia and/or peripheral nerves can be an adjuvant therapy for PLP.

CONCLUSIONS

Multimodal approaches combining pharmacotherapy, surgery and invasive neuromodulation procedures would appear to be the most promising strategy for preventive and treating PLP and RLP. Future efforts should focus on cross-disciplinary education to increase awareness of treatment options exploring best practices for preventing pain at the time of amputation and enhancing treatment of chronic postamputation pain.

Regenerative Peripheral Nerve Interface Surgery for the Management of Chronic Posttraumatic Neuropathic Pain

Chronic pain resulting from peripheral nerve injury remains a common issue in the United States and affects 7 to 10% of the population. Regenerative Peripheral Nerve Interface (RPNI) surgery is an innovative surgical procedure designed to treat posttraumatic neuropathic pain, particularly when a symptomatic neuroma is present on clinical exam. RPNI surgery involves implantation of a transected peripheral nerve into an autologous free muscle graft to provide denervated targets to regenerating axons. RPNI surgery has been found in animal and human studies to be highly effective in addressing postamputation pain. While most studies have reported its uses in the amputation patient population for the treatment of neuroma and phantom limb pain, RPNI surgery has recently been used to address refractory headache, postmastectomy pain, and painful donor sites from the harvest of neurotized flaps. This review summarizes the current understanding of RPNI surgery for the treatment of chronic neuropathic pain.

Primary Targeted Muscle Reinnervation in Above-Knee Amputations in Patients with Unsalvageable Limbs from Limb-Threatening Ischemia or Infection

BACKGROUND

 Amputees frequently suffer from chronic pain in both their residual limbs (RLP) and phantom limbs (PLP) following their amputation. Targeted muscle reinnervation (TMR) is a nerve transfer technique that has been demonstrated to improve pain secondarily and at time of amputation. The goal of this study is to report on the efficacy of primary TMR at time of above-knee level amputations in the setting of limb-threatening ischemia or infection.

METHODS

 This is a retrospective review of a single-surgeon experience with TMR in patients undergoing through- or above-knee level amputations from January 2018 to June 2021. Patient charts were reviewed for the comorbidities in the Charlson Comorbidity Index. Postoperative notes were assayed for presence and absence of RLP and PLP, overall pain severity, chronic narcotic use, ambulatory status, and complications. A control group of patients undergoing lower limb amputation who did not receive TMR from January 2014 to December 2017 was used for comparison.

RESULTS

 Forty-one patients with through- or above-knee level amputations and primary TMR were included in this study. The tibial and common peroneal nerves were transferred in all cases to motor branches to the gastrocnemius, semimembranosus, semitendinosus, and biceps femoris. Fifty-eight patients with through- or above-knee level amputations without TMR were included for comparison. The TMR group had significantly less overall pain (41.5 vs. 67.2%, p = 0.01), RLP (26.8 vs. 44.8%, p = 0.04), and PLP (19.5 vs. 43.1%, p = 0.02). There were no significant differences in complication rates.

CONCLUSION

 TMR can safely and effectively be performed at time of a through- and above-knee level amputation and improves pain outcomes.

Use of virtual reality for the management of phantom limb pain: a systematic review

PURPOSE

To summarize the research on the effectiveness of virtual reality (VR) therapy for the management of phantom limb pain (PLP).

METHODS

Three databases (SCOPUS, Ovid Embase, and Ovid MEDLINE) were searched for studies investigating the use of VR therapy for the treatment of PLP. Original research articles fulfilling the following criteria were included: (i) patients 18 years and older; (ii) all etiologies of amputation; (iii) any level of amputation; (iv) use of immersive VR as a treatment modality for PLP; (v) self-reported objective measures of PLP before and after at least one VR session; (vi) written in English.

RESULTS

A total of 15 studies were included for analysis. Fourteen studies reported decreases in objective pain scores following a single VR session or a VR intervention consisting of multiple sessions. Moreover, combining VR with tactile stimulation had a larger beneficial effect on PLP compared with VR alone.

CONCLUSIONS

Based on the current literature, VR therapy has the potential to be an effective treatment modality for the management of PLP. However, the low quality of studies, heterogeneity in subject population and intervention type, and lack of data on long-term relief make it difficult to draw definitive conclusions.IMPLICATION FOR REHABILITATIONVirtual reality (VR) therapy has emerged as a new potential treatment option for phantom limb pain (PLP) that circumvents some limitations of mirror therapy.VR therapy was shown to decrease PLP following a single VR session as well as after an intervention consisting of multiple sessions.The addition of vibrotactile stimuli to VR therapy may lead to larger decreases in PLP scores compared with VR therapy alone.

Brain white matter pathways of resilience to chronic back pain: a multisite validation

Chronic back pain (CBP) is a global health concern with significant societal and economic burden. While various predictors of back pain chronicity have been proposed, including demographic and psychosocial factors, neuroimaging studies have shown that brain characteristics can serve as robust predictors of CBP. However, large-scale, multisite validation of these predictors is currently lacking. In two independent longitudinal studies, we examined white matter diffusion imaging data and pain characteristics in patients with subacute back pain (SBP) over six- and 12-month periods. Diffusion data from individuals with CBP and healthy controls (HC) were analyzed for comparison. Whole-brain tract-based spatial statistics analyses revealed that a cluster in the right superior longitudinal fasciculus (SLF) tract had larger fractional anisotropy (FA) values in patients who recovered (SBPr) compared to those with persistent pain (SBPp), and predicted changes in pain severity. The SLF FA values accurately classified patients at baseline and follow-up in a third publicly available dataset (Area under the Receiver Operating Curve ~ 0.70). Notably, patients who recovered had FA values larger than those of HC suggesting a potential role of SLF integrity in resilience to CBP. Structural connectivity-based models also classified SBPp and SBPr patients from the three data sets (validation accuracy 67%). Our results validate the right SLF as a robust predictor of CBP development, with potential for clinical translation. Cognitive and behavioral processes dependent on the right SLF, such as proprioception and visuospatial attention, should be analyzed in subacute stages as they could prove important for back pain chronicity.

Cortical Reorganization after Limb Loss: Bridging the Gap between Basic Science and Clinical Recovery

Despite the increasing incidence and prevalence of amputation across the globe, individuals with acquired limb loss continue to struggle with functional recovery and chronic pain. A more complete understanding of the motor and sensory remodeling of the peripheral and central nervous system that occurs postamputation may help advance clinical interventions to improve the quality of life for individuals with acquired limb loss. The purpose of this article is to first provide background clinical context on individuals with acquired limb loss and then to provide a comprehensive review of the known motor and sensory neural adaptations from both animal models and human clinical trials. Finally, the article bridges the gap between basic science researchers and clinicians that treat individuals with limb loss by explaining how current clinical treatments may restore function and modulate phantom limb pain using the underlying neural adaptations described above. This review should encourage the further development of novel treatments with known neurological targets to improve the recovery of individuals postamputation.Significance Statement In the United States, 1.6 million people live with limb loss; this number is expected to more than double by 2050. Improved surgical procedures enhance recovery, and new prosthetics and neural interfaces can replace missing limbs with those that communicate bidirectionally with the brain. These advances have been fairly successful, but still most patients experience persistent problems like phantom limb pain, and others discontinue prostheses instead of learning to use them daily. These problematic patient outcomes may be due in part to the lack of consensus among basic and clinical researchers regarding the plasticity mechanisms that occur in the brain after amputation injuries. Here we review results from clinical and animal model studies to bridge this clinical-basic science gap.

Targeted Muscle Reinnervation at the Time of Amputation Decreases Recurrent Symptomatic Neuroma Formation

BACKGROUND

Targeted muscle reinnervation (TMR) is an effective technique for the prevention and management of phantom limb pain (PLP) and residual limb pain (RLP) among amputees. The purpose of this study was to evaluate symptomatic neuroma recurrence and neuropathic pain outcomes between cohorts undergoing TMR at the time of amputation (ie, acute) versus TMR following symptomatic neuroma formation (ie, delayed).

METHODS

A cross-sectional, retrospective chart review was conducted using patients undergoing TMR between 2015 and 2020. Symptomatic neuroma recurrence and surgical complications were collected. A subanalysis was conducted for patients who completed Patient-Reported Outcome Measurement Information System (PROMIS) pain intensity, interference, and behavior scales and an 11-point numeric rating scale (NRS) form.

RESULTS

A total of 105 limbs from 103 patients were identified, with 73 acute TMR limbs and 32 delayed TMR limbs. Nineteen percent of the delayed TMR group had symptomatic neuromas recur in the distribution of original TMR compared with 1% of the acute TMR group ( P < 0.05). Pain surveys were completed at final follow-up by 85% of patients in the acute TMR group and 69% of patients in the delayed TMR group. Of this subanalysis, acute TMR patients reported significantly lower PLP PROMIS pain interference ( P < 0.05), RLP PROMIS pain intensity ( P < 0.05), and RLP PROMIS pain interference ( P < 0.05) scores in comparison to the delayed group.

CONCLUSIONS

Patients who underwent acute TMR reported improved pain scores and a decreased rate of neuroma formation compared with TMR performed in a delayed fashion. These results highlight the promising role of TMR in the prevention of neuropathic pain and neuroma formation at the time of amputation.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Pain and Reorganization after Amputation: Is Interoceptive Prediction a Key?

There is an ongoing discussion on the relevance of brain reorganization following amputation for phantom limb pain. Recent attempts to provide explanations for seemingly controversial findings-specifically, maladaptive plasticity versus persistent functional representation as a complementary process-acknowledged that reorganization in the primary somatosensory cortex is not sufficient to explain phantom limb pain satisfactorily. Here we provide theoretical considerations that might help integrate the data reviewed and suppose a possible additional driver of the development of phantom limb pain-namely, an error in interoceptive predictions to somatosensory sensations and movements of the missing limb. Finally, we derive empirically testable consequences based on our considerations to guide future research.

Hybrid Bionic Nerve Interface for Application in Bionic Limbs

Intuitive and perceptual neuroprosthetic systems require a high degree of neural control and a variety of sensory feedback, but reliable neural interfaces for long-term use that maintain their functionality are limited. Here, a novel hybrid bionic interface is presented, fabricated by integrating a biological interface (regenerative peripheral nerve interface (RPNI)) and a peripheral neural interface to enhance the neural interface performance between a nerve and bionic limbs. This interface utilizes a shape memory polymer buckle that can be easily implanted on a severed nerve and make contact with both the nerve and the muscle graft after RPNI formation. It is demonstrated that this interface can simultaneously record different signal information via the RPNI and the nerve, as well as stimulate them separately, inducing different responses. Furthermore, it is shown that this interface can record naturally evoked signals from a walking rabbit and use them to control a robotic leg. The long-term functionality and biocompatibility of this interface in rabbits are evaluated for up to 29 weeks, confirming its promising potential for enhancing prosthetic control.

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.

Risk Factors Analysis of Phantom Limb Pain in Amputees with Malignant Tumors

Purpose

Postamputation neuropathic pain is a common disease in patients with malignant tumor amputation, seriously affecting amputees' quality of life and mental health. The objective of this study was to identify independent risk factors for phantom limb pain in patients with tumor amputation and to construct a risk prediction model.

Methods

Patients who underwent amputation due to malignant tumors from 2013 to 2023 were retrospectively analyzed and divided into phantom limb pain group and non-phantom limb pain group. To determine which preoperative factors would affect the occurrence of phantom limb pain, we searched for candidate factors by univariate analysis and used multivariate logistic regression analysis to identify independent factors and construct a predictive model. The receiver operating characteristic curve (ROC) was drawn to further evaluate the accuracy of the prediction model in evaluating the phantom limb pain after amputation of bone and soft tissue tumors.

Results

Multivariate analysis showed that age (OR, 1.054; 95% CI, 1.027 to 1.080), preoperative pain (OR, 5.773; 95% CI, 2.362 to 14.104), number of surgeries (OR, 3.425; 95% CI, 1.505 to 7.795), amputation site (OR, 5.848; 95% CI, 1.837 to 18.620), amputation level (OR, 8.031; 95% CI, 2.491 to 25.888) were independent risk factors for phantom limb pain for bone and soft tissue tumors. The the area under the curve (AUC) of this model was 0.834.

Conclusion

Risk factors for postoperative phantom limb pain were the site of amputation, proximal amputation, preoperative pain, multiple amputations, and older age. These factors will help surgeons to individualize and stratify phantom limb pain and help patients with risk counseling. In particular, an informed clinical decision targeting those modifiable factors can be considered when needed.

An Overview of the Body Schema and Body Image: Theoretical Models, Methodological Settings and Pitfalls for Rehabilitation of Persons with Neurological Disorders

Given the widespread debate on the definition of the terms "Body Schema" and "Body Image", this article presents a broad overview of the studies that have investigated the nature of these types of body representations, especially focusing on the innovative information about these two representations that could be useful for the rehabilitation of patients with different neurological disorders with motor deficits (especially those affecting the upper limbs). In particular, we analyzed (i) the different definitions and explicative models proposed, (ii) the empirical settings used to test them and (iii) the clinical and rehabilitative implications derived from the application of interventions on specific case reports. The growing number of neurological diseases with motor impairment in the general population has required the development of new rehabilitation techniques and a new phenomenological paradigm placing body schema as fundamental and intrinsic parts for action in space. In this narrative review, the focus was placed on evidence from the application of innovative rehabilitation techniques and case reports involving the upper limbs, as body parts particularly involved in finalistic voluntary actions in everyday life, discussing body representations and their functional role.

Outcomes of Targeted Muscle Reinnervation and Regenerative Peripheral Nerve Interfaces for Chronic Pain Control in the Oncologic Amputee Population

BACKGROUND

Outcomes of targeted muscle reinnervation (TMR) and regenerative peripheral nerve interface (RPNI) in the oncologic population are limited. We sought to examine the safety and effectiveness of TMR and RPNI in controlling postamputation pain in the oncologic population.

STUDY DESIGN

A retrospective cohort study of consecutive patients who underwent oncologic amputation followed by immediate TMR or RPNI was conducted from November 2018 to May 2022. The primary study outcome was postamputation pain, assessed using the Numeric Pain Scale and Patient-Reported Outcomes Measurement Information System (PROMIS) for residual limb pain (RLP) and phantom limb pain (PLP). Secondary outcomes included postoperative complications, tumor recurrence, and opioid use.

RESULTS

Sixty-three patients were evaluated for a mean follow-up period of 11.3 months. The majority of patients (65.1%) had a history of previous limb salvage. At final follow-up, patients had an average Numeric Pain Scale score for RLP of 1.3 ± 2.2 and for PLP, 1.9 ± 2.6. The final average raw PROMIS measures were pain intensity 6.2 ± 2.9 (T-score 43.5), pain interference 14.6 ± 8.3 (T-score 55.0), and pain behavior 39.0 ± 22.1 (T-score 53.4). Patient opioid use decreased from 85.7% preoperatively to 37.7% postoperatively and morphine milligram equivalents decreased from a mean of 52.4 ± 53.0 preoperatively to 20.2 ± 38.4 postoperatively.

CONCLUSIONS

In the oncologic population TMR and RPNI are safe surgical techniques associated with significant reductions in RLP, PLP, and improvements in patient-reported outcomes. This study provides evidence for the routine incorporation of TMR and RPNI in the multidisciplinary care of oncologic amputees.

Free Fillet Flap of Lower Extremity: 38 Amputations with Seven Examples of Targeted Muscle Reinnervation and Regenerative Peripheral Nerve Interfaces

BACKGROUND

Extremely high-level lower extremity amputations are rare procedures that require significant soft-tissue and bony reconstruction. This study describes the use of fillet flaps for oncologic reconstruction and the incorporation of targeted muscle reinnervation (TMR) and regenerative peripheral nerve interfaces (RPNIs) for chronic pain prevention.

METHODS

The authors performed a retrospective review of patients who underwent lower extremity fillet flaps at MD Anderson Cancer Center from January of 2004 through April of 2021. Surgical outcomes were summarized and compared. Numeric rating scale and patient-reported outcomes measures were collected.

RESULTS

Thirty-eight fillet flaps were performed for lower extremity reconstruction. Extirpative surgery included external hemipelvectomy (42%), external hemipelvectomy with sacrectomy (32%), and supratrochanteric above-knee amputation (26%). Median defect size was 600 cm 2 , and 50% included a bony component. Twenty-one patients (55%) experienced postoperative complications, with 16 requiring operative intervention. There was an increased trend toward complications in patients with preoperative radiotherapy, although this was not significant (44% versus 65%; P = 0.203). Seven patients underwent TMR or RPNI. In these patients, the mean numeric rating scale residual limb pain score was 2.8 ± 3.4 ( n = 5; range, 0 to 4/10) and phantom limb pain was 4 ± 3.2 ( n = 6; range, 0 to 7/10). The mean Patient-Reported Outcomes Measures Information Systems T scores were as follows: pain intensity, 50.8 ± 10.6 ( n = 6; range, 30.7 to 60.5); pain interference, 59.2 ± 12.1 ( n = 5; range, 40.7 to 70.1); and pain behavior, 62.3 ± 6.7 ( n = 3; range, 54.6 to 67.2).

CONCLUSIONS

Lower limb fillet flaps are reliable sources of bone, soft tissue, and nerve for reconstruction of oncologic amputation. TMR or RPNI are important new treatment adjuncts that should be considered during every amputation.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Vibrotactile Feedback for a Person with Transradial Amputation and Visual Loss: A Case Report

Background and Objectives: After major upper-limb amputation, people face challenges due to losing tactile information and gripping function in their hands. While vision can confirm the success of an action, relying on it diverts attention from other sensations and tasks. This case report presents a 30-year-old man with traumatic, complete vision loss and transradial left forearm amputation. It emphasizes the importance of restoring tactile abilities when visual compensation is impossible. Materials and Methods: A prototype tactile feedback add-on system was developed, consisting of a sensor glove and upper arm cuff with related vibration actuators. Results: We found a 66% improvement in the Box and Blocks test and an overall functional score increase from 30% to 43% in the Southampton Hand Assessment Procedure with feedback. Qualitative improvements in bimanual activities, ergonomics, and reduced reliance on the unaffected hand were observed. Incorporating the tactile feedback system improved the precision of grasping and the utility of the myoelectric hand prosthesis, freeing the unaffected hand for other tasks. Conclusions: This case demonstrated improvements in prosthetic hand utility achieved by restoring peripheral sensitivity while excluding the possibility of visual compensation. Restoring tactile information from the hand and fingers could benefit individuals with impaired vision and somatosensation, improving acceptance, embodiment, social integration, and pain management.

Integration of proprioception in upper limb prostheses through non-invasive strategies: a review

Proprioception plays a key role in moving our body dexterously and effortlessly. Nevertheless, the majority of investigations evaluating the benefits of providing supplemental feedback to prosthetics users focus on delivering touch restitution. These studies evaluate the influence of touch sensation in an attempt to improve the controllability of current robotic devices. Contrarily, investigations evaluating the capabilities of proprioceptive supplemental feedback have yet to be comprehensively analyzed to the same extent, marking a major gap in knowledge within the current research climate. The non-invasive strategies employed so far to restitute proprioception are reviewed in this work. In the absence of a clearly superior strategy, approaches employing vibrotactile, electrotactile and skin-stretch stimulation achieved better and more consistent results, considering both kinesthetic and grip force information, compared with other strategies or any incidental feedback. Although emulating the richness of the physiological sensory return through artificial feedback is the primary hurdle, measuring its effects to eventually support the integration of cumbersome and energy intensive hardware into commercial prosthetic devices could represent an even greater challenge. Thus, we analyze the strengths and limitations of previous studies and discuss the possible benefits of coupling objective measures, like neurophysiological parameters, as well as measures of prosthesis embodiment and cognitive load with behavioral measures of performance. Such insights aim to provide additional and collateral outcomes to be considered in the experimental design of future investigations of proprioception restitution that could, in the end, allow researchers to gain a more detailed understanding of possibly similar behavioral results and, thus, support one strategy over another.

Stimulation of peroneal nerves reveals maintained somatosensory representation in transtibial amputees

Introduction

Several studies have found changes in the organization of the primary somatosensory cortex (SI) after amputation. This SI reorganization was mainly investigated by stimulating neighboring areas to amputation. Unexpectedly, the somatosensory representation of the deafferented limb has rarely been directly tested.

Methods

We stimulated the truncated peroneal nerve in 24 unilateral transtibial amputees and 15 healthy controls. The stimulation intensity was adjusted to make the elicited percept comparable between both stimulation sides. Neural sources of the somatosensory-evoked magnetic fields (SEFs) to peroneal stimulation were localized in the contralateral foot/leg areas of SI in 19 patients and 14 healthy controls.

Results

We demonstrated the activation of functionally preserved cortical representations of amputated lower limbs. None of the patients reported evoked phantom limb pain (PLP) during stimulation. Stimulation that evoked perceptions in the foot required stronger intensities on the amputated side than on the intact side. In addition to this, stronger stimulation intensities were required for amputees than for healthy controls. Exploratorily, PLP intensity was neither associated with stimulation intensity nor dipole strength nor with differences in Euclidean distances (between SEF sources of the healthy peroneus and mirrored SEF sources of the truncated peroneus).

Discussion

Our results provide hope that the truncated nerve may be used to establish both motor control and somatosensory feedback via the nerve trunk when a permanently functional connection between the nerve trunk and the prosthesis becomes available.

Functional and structural synaptic remodeling mechanisms underlying somatotopic organization and reorganization in the thalamus

The somatosensory system organizes the topographic representation of body maps, termed somatotopy, at all levels of an ascending hierarchy. Postnatal maturation of somatotopy establishes optimal somatosensation, whereas deafferentation in adults reorganizes somatotopy, which underlies pathological somatosensation, such as phantom pain and complex regional pain syndrome. Here, we focus on the mouse whisker somatosensory thalamus to study how sensory experience shapes the fine topography of afferent connectivity during the critical period and what mechanisms remodel it and drive a large-scale somatotopic reorganization after peripheral nerve injury. We will review our findings that, following peripheral nerve injury in adults, lemniscal afferent synapses onto thalamic neurons are remodeled back to immature configuration, as if the critical period reopens. The remodeling process is initiated with local activation of microglia in the brainstem somatosensory nucleus downstream to injured nerves and heterosynaptically controlled by input from GABAergic and cortical neurons to thalamic neurons. These fruits of thalamic studies complement well-studied cortical mechanisms of somatotopic organization and reorganization and unveil potential intervention points in treating pathological somatosensation.

A case of phantom pain and stump pain that was effectively controlled by ultrasound-guided ulnar and median peripheral nerve blocks

Phantom limb pain and stump pain are often intractable, and their incidences are relatively high. We report a case of a patient with phantom limb and stump pain of the finger, who was successfully treated by peripheral nerve blocks. The patient was a male truck driver in his fifties, who had his left annular finger amputated in an accident 2 years previously. Owing to poor pain control at the stump of his finger, he was referred to our department. The initial examination revealed pain about numerical rating scale (NRS) 6/10 in the left annular finger transection as well as allodynia. Although some pain relief had been observed with postoperative medication, he still had persistent resting pain of about NRS 4/10. Therefore, blocks of the ulnar nerve and median nerve were performed. After the blocks were performed, the pain improved to NRS 1 to 2/10, and pain upon movement also almost disappeared. Peripheral nerve blocks can be a useful treatment modality for phantom limb pain and stump pain in the fingers, as in this case.

Regenerative Peripheral Nerve Interface Surgery: Anatomic and Technical Guide

Regenerative peripheral nerve interface (RPNI) surgery has been demonstrated to be an effective tool as an interface for neuroprosthetics. Additionally, it has been shown to be a reproducible and reliable strategy for the active treatment and for prevention of neuromas. The purpose of this article is to provide a comprehensive review of RPNI surgery to demonstrate its simplicity and empower reconstructive surgeons to add this to their armamentarium. This article discusses the basic science of neuroma formation and prevention, as well as the theory of RPNI. An anatomic review and discussion of surgical technique for each level of amputation and considerations for other etiologies of traumatic neuromas are included. Lastly, the authors discuss the future of RPNI surgery and compare this with other active techniques for the treatment of neuromas.

Referred Sensation Areas in Bilateral Upper Limb Amputee

Phantom limb pain (PLP) following amputation considerably reduces the quality of life, given a difficult to treat pain of highly variate profile. The loss of sensory input induces a complex pattern of neuroplastic changes of the sensory neural pathways and their central projections. Referred sensation areas (RSAs) may occur on the stump as a consequence of amputation, providing a direct path towards the altered central sensory projections. Modulated electrical stimulation of RSAs was investigated in a long-term experiment in the case of a 62 years-old participant with bilateral upper limb amputation due to traumatic injury. RSAs were investigated using mechanical (vibration and pressure) and electrical stimuli over five sessions within a five weeks period. Further test of sensations induced by steady state and modulated electrical stimuli was performed during additional 4 sessions. Location and features of RSAs were highly dependent on the type of stimulus and time of delivery between sessions.Clinical Relevance- The case study presents a variety of types and locations of the sensation induced by electrical and mechanical stimuli that may eventually be used as artificially generated sensory input as individualized alternative form of therapy for PLP alleviation. Furthermore, possible multichannel stimulus delivery on RSAs on both arms and the cross-over effect of the bilateral amputation in perception of the induced sensation in the opposite phantom hand may be considered in dedicated design of an experimental setup that may possibly help investigation of mechanisms for PLP.

Managing acute phantom limb pain with transcutaneous electrical nerve stimulation: a case report

INTRODUCTION

Phantom limb pain is characterized by painful sensations in the amputated limb. The clinical presentation of acute phantom limb pain may differ from that of patients with chronic phantom limb pain. The variation observed implies that acute phantom limb pain may be driven by peripheral mechanisms, indicating that therapies focused on the peripheral nervous system might be successful in reducing pain.

CASE PRESENTATION

A 36-year-old African male with acute phantom limb pain in the left lower limb, was treated with transcutaneous electrical nerve stimulation.

CONCLUSION

The assessment results of the presented case and the evidence on acute phantom limb pain mechanisms contribute to the current body of literature, indicating that acute phantom limb pain presents differently to chronic phantom limb pain. These findings emphasize the importance of testing treatments that target the peripheral mechanisms responsible for phantom limb pain in relevant individuals with acquired amputations.

Motor cortical functional connectivity changes due to short-term immobilization of upper limb: an fNIRS case report

Introduction

A short-term immobilization of one hand affects musculoskeletal functions, and the associated brain network adapts to the alterations happening to the body due to injuries. It was hypothesized that the injury-associated temporary disuse of the upper limb would alter the functional interactions of the motor cortical processes and will produce long-term changes throughout the immobilization and post-immobilization period.

Methods

The case participant (male, 12 years old, right arm immobilized for clavicle fracture) was scanned using optical imaging technology of fNIRS over immobilization and post-immobilization. Pre-task data was collected for 3 min for RSFC analysis, processed, and analyzed using the Brain AnalyzIR toolbox. Connectivity was measured using Pearson correlation coefficients (R) from NIRS Toolbox's connectivity module.

Results

The non-affected hand task presented an increased ipsilateral response during the immobilization period, which then decreased over the follow-up visits. The right-hand task showed a bilateral activation pattern following immobilization, but the contralateral activation pattern was restored during the 1-year follow-up visit. Significant differences in the average connection strength over the study period were observed. The average Connection strength decreased from the third week of immobilization and continued to be lower than the baseline value. Global network efficiency decreased in weeks two and three, while the network settled into a higher efficient state during the follow-up periods after post-immobilization.

Discussion

Short-term immobilization of the upper limb is shown to have cortical changes in terms of activations of brain regions as well as connectivity. The short-term dis-use of the upper limb has shifted the unilateral activation pattern to the bilateral coactivation of the motor cortex from both hemispheres. Resting-state data reveals a disruption in the motor cortical network during the immobilization phase, and the network is reorganized into an efficient network over 1 year after the injury. Understanding such cortical reorganization could be informative for studying the recovery from neurological disorders affecting motor control in the future.

The Peripheral Nerve Surgeon's Role in the Management of Neuropathic Pain

Neuropathic pain (NP) underlies significant morbidity and disability worldwide. Although pharmacologic and functional therapies attempt to address this issue, they remain incompletely effective for many patients. Peripheral nerve surgeons have a range of techniques for intervening on NP. The aim of this review is to enable practitioners to identify patients with NP who might benefit from surgical intervention. The workup for NP includes patient history and specific physical examination maneuvers, as well as imaging and diagnostic nerve blocks. Once diagnosed, there is a range of options surgeons can utilize based on specific causes of NP. These techniques include nerve decompression, nerve reconstruction, nerve ablative techniques, and implantable nerve-modulating devices. In addition, there is an emerging role for preoperative involvement of peripheral nerve surgeons for cases known to carry a high risk of inducing postoperative NP. Lastly, we describe the ongoing work that will enable surgeons to expand their armamentarium to better serve patients with NP.

[Mother brain: Bayesian theory of maternal interoception during pregnancy and postpartum]

The perinatal period, including pregnancy and postpartum, causes major morphological, endocrinal, and thermal transitions in women. As the fetus grows, abdominal muscle fibers stretch, internal organs such as the bladder or colon move, and the uterine anatomy changes. Many of these changes involve interoception, the perception of internal body signals such as muscle and visceral sensations. Despite the importance of these interoceptive signals, few studies have explored perinatal interoception. We propose an innovative theory of maternal interoception based on recent findings in neuroscience. We show that interoceptive signals processing during pregnancy is crucial for understanding perinatal phenomenology and psychopathology, such as maternal perception of fetal movements, maternal-infant bonding, denial of pregnancy, phantom fetal movements after childbirth, pseudocyesis or even puerperal delusion. Knowing the importance of these interoceptive mechanisms, clinicians in obstetrics, gynecology and mental health should be particularly vigilant to maternal interoception during the perinatal period.

The medial prefrontal cortex and the cardiac baroreflex activity: physiological and pathological implications

The cardiac baroreflex is an autonomic neural mechanism involved in the modulation of the cardiovascular system. It influences the heart rate and peripheral vascular resistance to preserve arterial blood pressure within a narrow variation range. This mechanism is mainly controlled by medullary nuclei located in the brain stem. However, supramedullary areas, such as the ventral portion of medial prefrontal cortex (vMPFC), are also involved. Particularly, the glutamatergic NMDA/NO pathway in the vMPFC can facilitate baroreflex bradycardic and tachycardic responses. In addition, cannabinoid receptors in this same area can reduce or increase those cardiac responses, possibly through alteration in glutamate release. This vMPFC network has been associated to cardiovascular responses during stressful situations. Recent results showed an involvement of glutamatergic, nitrergic, and endocannabinoid systems in the blood pressure and heart rate increases in animals after aversive conditioning. Consequently, baroreflex could be modified by the vMPFC neurotransmission during stressful situations, allowing necessary cardiovascular adjustments. Remarkably, some mental, neurological and neurodegenerative disorders can involve damage in the vMPFC, such as posttraumatic stress disorder, major depressive disorder, Alzheimer's disease, and neuropathic pain. These pathologies are also associated with alterations in glutamate/NO release and endocannabinoid functions along with baroreflex impairment. Thus, the vMPFC seems to play a crucial role on the baroreflex control, either during pathological or physiological stress-related responses. The study of baroreflex mechanism under such pathological view may be helpful to establish causality mechanisms for the autonomic and cardiovascular imbalance found in those conditions. It can explain in the future the reasons of the high cardiovascular risk some neurological and neurodegenerative disease patients undergo. Additionally, the present work offers insights on the possible contributions of vMPFC dysfunction on baroreflex alterations, which, in turn, may raise questions in what extent other brain areas may play a role in autonomic deregulation under such pathological situations.

Prevalence of Phantom Phenomena in Congenital and Early-Life Amputees

Phantom limb pain (PLP) is a common consequence of the amputation of a limb. Persons with congenital limb absence (congenital amputees) or an acquired limb amputation at an early age seem to rarely experience PLP. However, the number of available studies and their sample sizes are low. In the present cross-sectional study, we assessed the presence of several phantom phenomena in a sample of 99 adult unilateral congenital amputees (con) of whom 34 had a limb correction later in life (limbc) and 153 adult participants with a unilateral amputation before the age of 6 years (subgroups: amputation between birth and 2 years (0-2y; n = 48), 3-4 years (3-4y; n = 46), and 5 to 6 years (5-6y; n = 59)). We found a higher prevalence and intensity of PLP in the 5-6y group compared to the other groups. Residual limb pain (RLP) intensity was higher in the 3 to 4 y and 5 to 6 y groups compared to the con group. Non-painful phantom limb sensation (PLS) intensity and telescoping intensity were higher in the 5 to 6 y group compared to the con and 0 to 2 y groups. Our results indicate that PLP prevalence as well as intensity is low when the limb loss happened before the age of 5 years. PERSPECTIVE: The prevalence of phantom limb pain, residual limb pain, and non-painful phantom limb sensation in congenital amputees and participants with an amputation early in life is low. This might be due to the missing or reduced nociceptive input from the residual limb to the brain and higher development-associated adaptability of the somatosensory system.

Assessment of efficiency of mirror therapy in preventing phantom limb pain in patients undergoing below-knee amputation surgery-a randomized clinical trial

PURPOSE AND OBJECTIVES

Phantom limb pain (PLP) is a major cause of physical limitation and disability accounting for about 85% of amputated patients. Mirror therapy is used as a therapeutic modality for patients with phantom limb pain. Primary objective was to study the incidence of PLP at 6 months following below-knee amputation between the mirror therapy group and control group.

METHODS

Patients posted for below-knee amputation surgery were randomized into two groups. Patients allocated to group M received mirror therapy in post-operative period. Two sessions of therapy were given per day for 7 days and each session lasted for 20 min. Patients who developed pain from the missing portion of the amputated limb were considered to have PLP. All patients were followed up for six months and the time of occurrence of PLP and intensity of the pain were recorded among other demographic factors.

RESULTS

A total of 120 patients completed the study after recruitment. The demographic parameters were comparable between the two groups. Overall incidence of phantom limb pain was significantly higher in the control group (Group C) when compared to the mirror therapy (Group M) group [Group M = 7 (11.7%) vs Group C = 17 (28.3%); p = 0.022]. Intensity of PLP measured on the Numerical Rating Scale (NRS) was significantly lower at 3 months in Group M compared to Group C among patients who developed PLP [NRS - median (Inter quartile range): Group M 5 (4,5) vs Group C 6 (5,6); p 0.001].

CONCLUSION

Mirror therapy reduced the incidence of phantom limb pain when administered pre-emptively in patients undergoing amputation surgeries. The severity of the pain was also found to be lower at 3 months in patients who received pre-emptive mirror therapy.

TRIAL REGISTRATION

This prospective study was registered in the clinical trial registry of India.

TRIAL REGISTRATION NUMBER

CTRI/2020/07/026488.

Effect of a continuous perineural levobupivacaine infusion on pain after major lower limb amputation: a randomised double-blind placebo-controlled trial

OBJECTIVES

Randomised controlled trial of the effect of a perineural infusion of levobupivacaine on moderate/severe phantom limb pain 6 months after major lower limb amputation.

SETTING

Single-centre, UK university hospital.

PARTICIPANTS

Ninety patients undergoing above-knee and below-knee amputation for chronic limb threatening ischaemia under general anaesthesia. Exclusion criteria were patients having surgery under neuraxial anaesthesia; inability to operate a patient-controlled analgesia device or complete a Visual Analogue Scale; amputation for trauma or malignancy; or contraindication to levobupivacaine.

INTERVENTIONS

Either levobupivacaine 0.125% or saline 0.9% (10 mL bolus, infusion of 8 mL/hour for 96 hours) via a sciatic or posterior tibial nerve sheath catheter placed under direct vision during surgery.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome measure was the presence of phantom limb pain, residual limb pain and phantom limb sensations up to 6 months after amputation. Secondary outcome measures included early postoperative pain and morphine requirements after surgery.

RESULTS

Data from 81 participants were analysed; 6-month follow-up data were available for 62 patients. Pain and morphine requirements varied widely before and after amputation in both groups. The incidences of moderate/severe phantom limb pain, residual limb pain and phantom limb sensations were low from 6 weeks with no significant differences between groups in phantom limb pain at rest (OR 0.56, 95% CI 0.14 to 2.14, p=0.394) or movement (OR 0.58, 95% CI 0.15 to 2.21, p=0.425) at 6 months. Early postoperative pain scores were low in both groups with no between-group differences in residual limb pain or phantom limb sensations (rest or movement) at any time point. High postoperative morphine consumption was associated with worsening phantom limb pain both at rest (-17.51, 95% CI -24.29 to -10.74; p<0.001) and on movement (-18.54, 95% CI -25.58 to -11.49; p<0.001). The incidence of adverse effects related to the study was low in both groups: postoperative nausea, vomiting and sedation scores were similar, and there were no features of local anaesthetic toxicity.

CONCLUSIONS

Long-term phantom limb pain, residual limb pain and phantom limb sensations were not reduced significantly by perineural infusion of levobupivacaine, although the study was underpowered to show significant differences in the primary outcome. The incidence of phantom limb pain was lower than previously reported, possibly attributable to frequent assessment and early intervention to identify and treat postoperative pain when it occurred. There were large variations in postoperative pain scores, high requirements for analgesics before and after surgery and some problems maintaining recruitment and long -term follow-up. Knowledge of these potential problems should inform future research in this group of patients. Further work should investigate the association between perioperative morphine requirements and late phantom limb pain.

TRIAL REGISTRATION NUMBERS

EudraCT 2007-000619-27; ISRCTN68691928.

Resting state neurophysiology of agonist-antagonist myoneural interface in persons with transtibial amputation

The agonist-antagonist myoneural interface (AMI) is a novel amputation surgery that preserves sensorimotor signaling mechanisms of the central-peripheral nervous systems. Our first neuroimaging study investigating AMI subjects (Srinivasan et al., Sci. Transl. Med. 2020) focused on task-based neural signatures, and showed evidence of proprioceptive feedback to the central nervous system. The study of resting state neural activity helps non-invasively characterize the neural patterns that prime task response. In this first study on resting state fMRI in AMI subjects, we compared resting state functional connectivity in patients with transtibial AMI (n=12) and traditional (n=7) amputations, as well as biologically intact control subjects (n=10). We hypothesized that the AMI surgery will induce functional network reorganization that significantly differs from the traditional amputation surgery and also more closely resembles the neural configuration of controls. We found AMI subjects to have lower connectivity with salience and motor seed regions compared to traditional amputees. Additionally, with connections affected in traditional amputees, AMI subjects exhibited a connectivity pattern more closely resembling controls. Lastly, sensorimotor connectivity in amputee cohorts was significantly associated with phantom sensation (R2=0.7, p=0.0008). These findings provide researchers and clinicians with a critical mechanistic understanding of the effects of the AMI surgery on the brain at rest, spearheading future research towards improved prosthetic control and embodiment.

Comparative Effects of Interventions on Phantom Limb Pain: A Network Meta-Analysis

BACKGROUND

Phantom limb pain (PLP) is a common type of chronic pain that occurs after limb amputation. Many treatment approaches are available; however, the treatment of PLP is still a challenge. This study aimed to quantify and rank the efficacy of interventions for phantom limb pain.

METHODS

A comprehensive literature search was performed using the databases of PubMed, MEDLINE, Embase, Web of Science, and Cochrane. A network meta-analysis was applied to formulate direct and indirect comparisons among interventions for PLP.

RESULTS

Twenty-two studies comprising 662 patients and 13 different interventions were included in this study. The mirror therapy (MT) (-1.00; 95% confidence interval, -1.94 to -0.07) and MT + phantom exercise (PE) (-6.05; 95% confidence interval, -8.29 to -3.81) group presented significantly lower pain intensity compared with placebo. In SUCRA (surface under the cumulative ranking curve) analysis, the MT+PE and neuromodulation techniques groups had the highest SUCRA value (81.2).

CONCLUSIONS

Our results suggest that MT is the most optimal treatment for PLP, and a combination of therapies would enhance the therapeutic effect.

Percutaneous treatments for residual and/or phantom limb pain in adults with lower-extremity amputations: A narrative review

Residual limb pain (RLP) and phantom limb pain (PLP) profoundly affect the lives of many individuals who have undergone lower- or upper-extremity amputation. Despite the considerable impact of RLP/PLP on quality of life in persons with amputation, there have been few attempts to evaluate the efficacy of percutaneous interventions in the treatment of RLP and/or PLP. This narrative review evaluates the effectiveness of percutaneous treatments for RLP and/or PLP in patients after lower-extremity amputation. Peripheral nerve stimulation, alcohol neurolysis, conventional thermal radiofrequency ablation, perineural corticosteroid injection, botulinum toxin injection, and etanercept injection were associated with varying success rates. Wide confidence intervals and small treatment cohorts impede assessments of overall success. High-quality studies of nonsurgical, percutaneous treatments for RLP and/or PLP are lacking. Well-designed randomized controlled trials and large cohort studies with comparison groups using validated outcomes are needed to determine the effectiveness of nonsurgical interventions for the treatment of RLP and PLP.

Adult neuroplasticity employs developmental mechanisms

Although neural plasticity is now widely studied, there was a time when the idea of adult plasticity was antithetical to the mainstream. The essential stumbling block arose from the seminal experiments of Hubel and Wiesel who presented convincing evidence that there existed a critical period for plasticity during development after which the brain lost its ability to change in accordance to shifts in sensory input. Despite the zeitgeist that mature brain is relatively immutable to change, there were a number of examples of adult neural plasticity emerging in the scientific literature. Interestingly, some of the earliest of these studies involved visual plasticity in the adult cat. Even earlier, there were reports of what appeared to be functional reorganization in adult rat somatosensory thalamus after dorsal column lesions, a finding that was confirmed and extended with additional experimentation. To demonstrate that these findings reflected more than a response to central injury, and to gain greater control of the extent of the sensory loss, peripheral nerve injuries were used that eliminated ascending sensory information while leaving central pathways intact. Merzenich, Kaas, and colleagues used peripheral nerve transections to reveal unambiguous reorganization in primate somatosensory cortex. Moreover, these same researchers showed that this plasticity proceeded in no less than two stages, one immediate, and one more protracted. These findings were confirmed and extended to more expansive cortical deprivations, and further extended to the thalamus and brainstem. There then began a series of experiments to reveal the physiological, morphological and neurochemical mechanisms that permitted this plasticity. Ultimately, Mowery and colleagues conducted a series of experiments that carefully tracked the levels of expression of several subunits of glutamate (AMPA and NMDA) and GABA (GABAA and GABAB) receptor complexes in primate somatosensory cortex at several time points after peripheral nerve injury. These receptor subunit mapping experiments revealed that membrane expression levels came to reflect those seen in early phases of critical period development. This suggested that under conditions of prolonged sensory deprivation the adult cells were returning to critical period like plastic states, i.e., developmental recapitulation. Here we outline the heuristics that drive this phenomenon.

Endometriosis and Opioid Receptors: Are Opioids a Possible/Promising Treatment for Endometriosis?

Endometriosis (EM), defined as the presence of endometrial-like tissue with surrounding smooth muscle cells outside the uterus, is a disregarded gynecological disease reported to affect 6-10% of women of reproductive age, with 30-50% of them suffering from chronic pelvic pain and infertility. Since the exact pathogenic mechanisms of EM are still unclear, no curative therapy is available. As pain is an important factor in EM, optimal analgesia should be sought, which to date has been treated primarily with non-steroidal anti-inflammatory drugs (NSAIDs), metamizole or, in extreme cases, opioids. Here, we review the pain therapy options, the mechanisms of pain development in EM, the endogenous opioid system and pain, as well as the opioid receptors and EM-associated pain. We also explore the drug abuse and addiction to opioids and the possible use of NOP receptors in terms of analgesia and improved tolerability as a target for EM-associated pain treatment. Emerging evidence has shown a promising functional profile of bifunctional NOP/MOP partial agonists as safe and nonaddictive analgesics. However, until now, the role of NOP receptors in EM has not been investigated. This review offers a thought which still needs further investigation but may provide potential options for relieving EM-associated pain.

The experience of sensorimotor integration of a lower limb sensory neuroprosthesis: A qualitative case study

Introduction

Lower limb prosthesis users often struggle to navigate uneven terrain or ambulate in low light conditions where it can be challenging to rely on visual cues for balance and walking. Sensory feedback about foot-floor interactions may allow users to reduce reliance on secondary sensory cues and improve confidence and speed when navigating difficult terrain. Our group has developed a Sensory Neuroprosthesis (SNP) to restore sensation to people with lower limb amputation by pairing electrical stimulation of nerves in the residual limb applied via implanted neurotechnology with pressure sensors in the insole of a standard prosthesis. Stimulation applied to the nerves evoked sensations perceived as originating on the missing leg and foot.

Methods

This qualitative case study reports on the experiences of a 68-year-old with a unilateral trans-tibial amputation who autonomously used the SNP at home for 31 weeks. Interview data collected throughout the study period was analyzed using a grounded theory approach with constant comparative methods to understand his experience with this novel technology and its impacts on his daily life.

Results

A conceptual model was developed that explained the experience of integrating SNP-provided sensory feedback into his body and motor plans. The model described the requirements of integration, which were a combination of a low level of mental focus and low stimulation levels. While higher levels of stimulation and focus could result in distinct sensory percepts and various phantom limb experiences, optimal integration was associated with SNP-evoked sensation that was not readily perceivable. Successful sensorimotor integration of the SNP resulted in improvements to locomotion, a return to a more normal state, an enhancement of perceived prosthesis utility, and a positive outlook on the experience.

Discussion

These outcomes emerged over the course of the nearly 8 month study, suggesting that findings from long-term home studies of SNPs may differ from those of short-term in-laboratory tests. Our findings on the experience of sensorimotor integration of the SNP have implications for the optimal training of SNP users and the future deployment of clinical SNP systems for long-term home use.