Phantom limb pain: thinking outside the (mirror) box

Clinical features of phantom limb pain in patients with lower limb amputation in a Spanish population

OBJECTIVES

The aim of this research is to present the clinical characteristics of phantom limb pain (PLP) in patients with amputation.

METHODS

A retrospective cross-sectional observational study of patients with lower limb amputation is presented. Patients between 18 and 80 years of age with unilateral or bilateral amputation between the years 2015 and 2019 were included. Demographic data, medical history, data related to the amputation, and related abnormal sensations were collected.

RESULTS

43 patients (34 men) and 53 amputees were studied, with a mean age of 62 years, with a time elapsed since amputation of 28 months. The most frequent cause of amputation was ischemic (70%). Twenty-three (60%) patients had PLP that began 1 month after amputation with a mean intensity of 3.9 on the VAS scale, in 15 patients the PLP was daily, three patients recognised the disappearance of PLP. 91% of the patients presented non-painful sensations in relation to the phantom limb. No differences were found in the development of the PLP between the 1st and 2nd amputation. A significant association was found between the development of PLP and residual limb pain.

CONCLUSIONS

PLP is a prevalent pathology among amputee patients, therefore multidisciplinary care with an active neurologic participation is essential. Studies are needed to deepen the knowledge of the factors that favour the development of PLP in order to focus early and targeted therapies to prevent the appearance of PLP.

Motor and parietal cortex activity responses to mirror visual feedback in patients with subacute stroke: An EEG study

Objective

To elucidate the immediate electrophysiological effects of mirror visual feedback (MVF) combined with or without touch task in subacute stroke.

Methods

Subacute stroke patients and healthy controls were recruited to participate in four grasping tasks (MVF or no MVF, combined with rubber ball or no ball) under electroencephalogram (EEG) monitoring. Event-related desynchronization (ERD) /event-related synchronization (ERS) and the lateralization index (LI) were utilized to observe the electrophysiological effects.

Results

MVF reduced ERD suppression in the contralateral primary motor cortex (M1) of stroke patients. This reduction was observed in the low mu band for the contralateral parietal cortex during pure MVF. The laterality effects in the low mu band under MVF was noted in M1 for stroke patients and in the parietal cortex for all participants.

Conclusions

MVF inhibits the excitability of the contralateral M1 for subacute stroke. MVF inhibit activities in the contralateral M1 and parietal cortex, and reestablished hemispheric balance in the low mu band.

Significance

MVF has an instantaneous effect on subacute stroke by inhibiting the excitability of the contralateral sensorimotor cortex. The attenuated ERD in the low mu band in contralateral M1 and parietal cortex may serve as biomarkers of MVF for stroke rehabilitation.

The brain's duck test in phantom percepts: Multisensory congruence in neuropathic pain and tinnitus

Chronic neuropathic pain and chronic tinnitus have been likened to phantom percepts, in which a complete or partial sensory deafferentation results in a filling in of the missing information derived from memory. 150 participants, 50 with tinnitus, 50 with chronic pain and 50 healthy controls underwent a resting state EEG. Source localized current density is recorded from all the sensory cortices (olfactory, gustatory, somatosensory, auditory, vestibular, visual) as well as the parahippocampal area. Functional connectivity by means of lagged phase synchronization is also computed between these regions of interest. Pain and tinnitus are associated with gamma band activity, reflecting prediction errors, in all sensory cortices except the olfactory and gustatory cortex. Functional connectivity identifies theta frequency connectivity between each of the sensory cortices except the chemical senses to the parahippocampus, but not between the individual sensory cortices. When one sensory domain is deprived, the other senses may provide the parahippocampal 'contextual' area with the most likely sound or somatosensory sensation to fill in the gap, applying an abductive 'duck test' approach, i.e., based on stored multisensory congruence. This novel concept paves the way to develop novel treatments for pain and tinnitus, using multisensory (i.e. visual, vestibular, somatosensory, auditory) modulation with or without associated parahippocampal targeting.

Virtual reality in functional neurological disorder: a theoretical framework and research agenda for use in the real world

Functional neurological disorder (FND) is a common and disabling condition at the intersection of neurology and psychiatry. Despite remarkable progress over recent decades, the mechanisms of FND are still poorly understood and there are limited diagnostic tools and effective treatments. One potentially promising treatment modality for FND is virtual reality (VR), which has been increasingly applied to a broad range of conditions, including neuropsychiatric disorders. FND has unique features, many of which suggest the particular relevance for, and potential efficacy of, VR in both better understanding and managing the disorder. In this review, we describe how VR might be leveraged in the treatment and diagnosis of FND (with a primary focus on motor FND and persistent perceptual-postural dizziness given their prominence in the literature), as well as the elucidation of neurocognitive mechanisms and symptom phenomenology. First, we review what has been published to date on the applications of VR in FND and related neuropsychiatric disorders. We then discuss the hypothesised mechanism(s) underlying FND, focusing on the features that are most relevant to VR applications. Finally, we discuss the potential of VR in (1) advancing mechanistic understanding, focusing specifically on sense of agency, attention and suggestibility, (2) overcoming diagnostic challenges and (3) developing novel treatment modalities. This review aims to develop a theoretical foundation and research agenda for the use of VR in FND that might be applicable or adaptable to other related disorders.

The effect of mirror therapy in the rehabilitation of flexor tendon injuries after primary surgical repair

OBJECTIVE

The aim of this study was to evaluate the effectiveness of mirror therapy and to provide a clinical basis for better functional recovery in the rehabilitation of patients with flexor tendon injury.

MATERIALS AND METHODS

Thirty patients were included and randomly divided between two groups: mirror therapy and conventional treatment. A physical therapy program consisting of whirlpool, ultrasound and transcutaneous electrical nerve stimulation was applied to both groups. In the mirror therapy group, flexor tendon gliding, blocking exercises, joint range of motion and resistance exercises were performed with the healthy hand via a mirror. In the conventional treatment group, the same exercises were performed with the affected hand without mirror. This treatment was continued for 12 sessions over 4 weeks. Joint range of motion, handgrip strength, pain, functionality, dexterity and kinesiophobia were evaluated before and after treatment.

RESULTS

More improvement was observed in the mirror therapy group in terms of pain on visual analog scale, Patient-Rated Wrist Evaluation, Hand Function Index and Disabilities of the Arm, Shoulder and Hand scores (p = 0.025, p = 0.004, p < 0.001 and p < 0.001, respectively). There was no significant difference between groups for the other parameters (Tampa Kinesiophobia Scale, Purdue Pegboard test, total active range movement, or handgrip strength: p > 0.05).

CONCLUSION

This study shows that mirror therapy in postoperative rehabilitation of flexor tendon injuries is more effective than conventional in terms of reducing the severity of pain and restoring hand function.

Does Ipsilateral Remapping Following Hand Loss Impact Motor Control of the Intact Hand?

What happens once a cortical territory becomes functionally redundant? We studied changes in brain function and behavior for the remaining hand in humans (male and female) with either a missing hand from birth (one-handers) or due to amputation. Previous studies reported that amputees, but not one-handers, show increased ipsilateral activity in the somatosensory territory of the missing hand (i.e., remapping). We used a complex finger task to explore whether this observed remapping in amputees involves recruiting more neural resources to support the intact hand to meet greater motor control demands. Using basic fMRI analysis, we found that only amputees had more ipsilateral activity when motor demand increased; however, this did not match any noticeable improvement in their behavioral task performance. More advanced multivariate fMRI analyses showed that amputees had stronger and more typical representation-relative to controls' contralateral hand representation-compared with one-handers. This suggests that in amputees, both hand areas work together more collaboratively, potentially reflecting the intact hand's efference copy. One-handers struggled to learn difficult finger configurations, but this did not translate to differences in univariate or multivariate activity relative to controls. Additional white matter analysis provided conclusive evidence that the structural connectivity between the two hand areas did not vary across groups. Together, our results suggest that enhanced activity in the missing hand territory may not reflect intact hand function. Instead, we suggest that plasticity is more restricted than generally assumed and may depend on the availability of homologous pathways acquired early in life.

The missing pieces: an investigation into the parallels between Charles Bonnet, phantom limb and tinnitus syndromes

Charles Bonnet syndrome (CBS) is a condition characterised by visual hallucinations of varying complexity on a background of vision loss. CBS research has gained popularity only in recent decades, despite evidence dating back to 1760. Knowledge of CBS among both the patient and professional populations unfortunately remains poor, and little is known of its underlying pathophysiology. CBS parallels two other better-known conditions that occur as a result of sensory loss: phantom limb syndrome (PLS) (aberrant sensation of the presence of a missing limb) and tinnitus (aberrant sensation of sound). As 'phantom' conditions, CBS, PLS and tinnitus share sensory loss as a precipitating factor, and, as subjective perceptual phenomena, face similar challenges to investigations. Thus far, these conditions have been studied separately from each other. This review aims to bridge the conceptual gap between CBS, PLS and tinnitus and seek common lessons between them. It considers the current knowledge base of CBS and explores the extent to which an understanding of PLS and tinnitus could provide valuable insights into the pathology of CBS (including the roles of cortical reorganisation, emotional and cognitive factors), and towards identifying effective potential management for CBS.

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.

Against cortical reorganisation

Neurological insults, such as congenital blindness, deafness, amputation, and stroke, often result in surprising and impressive behavioural changes. Cortical reorganisation, which refers to preserved brain tissue taking on a new functional role, is often invoked to account for these behavioural changes. Here, we revisit many of the classical animal and patient cortical remapping studies that spawned this notion of reorganisation. We highlight empirical, methodological, and conceptual problems that call this notion into doubt. We argue that appeal to the idea of reorganisation is attributable in part to the way that cortical maps are empirically derived. Specifically, cortical maps are often defined based on oversimplified assumptions of 'winner-takes-all', which in turn leads to an erroneous interpretation of what it means when these maps appear to change. Conceptually, remapping is interpreted as a circuit receiving novel input and processing it in a way unrelated to its original function. This implies that neurons are either pluripotent enough to change what they are tuned to or that a circuit can change what it computes. Instead of reorganisation, we argue that remapping is more likely to occur due to potentiation of pre-existing architecture that already has the requisite representational and computational capacity pre-injury. This architecture can be facilitated via Hebbian and homeostatic plasticity mechanisms. Crucially, our revised framework proposes that opportunities for functional change are constrained throughout the lifespan by the underlying structural 'blueprint'. At no period, including early in development, does the cortex offer structural opportunities for functional pluripotency. We conclude that reorganisation as a distinct form of cortical plasticity, ubiquitously evoked with words such as 'take-over'' and 'rewiring', does not exist.

The Efficacy of Graded Motor Imagery and Its Components on Phantom Limb Pain and Disability: A Systematic Review and Meta-Analysis

Introduction

Graded Motor Imagery (GMI) is a non-invasive and inexpensive therapy used to treat Phantom Limb Pain (PLP) by sequentially activating motor networks in such a way that movement and pain are unpaired. The objective of this systematic review was to critically appraise relevant data on the efficacy of GMI and its components for reducing PLP and disability in amputees.

Methods

We searched 11 electronic databases for controlled trials investigating GMI and its components in amputees with PLP from inception until February 2023. Two reviewers independently screened studies and extracted relevant data. Study-level data were entered using the inverse variance function of the Review Manager 5 and pooled with the random effects model.

Results

Eleven studies with varying risk of bias were eligible. No eligible study considered left/right judgement tasks in isolation. Studies showed no effect for imagined movements, but positive effects were seen for GMI [weighted mean difference: -21.29 (95%CI: -31.55, -11.02), I2= 0%] and mirror therapy [weighted mean difference: -8.55 (95%CI: -14.74, -2.35, I2= 61%]. A comparison of mirror therapy versus sham showed no difference [weighted mean difference: -4.43 (95%CI: -16.03, 7.16), I2= 51%].

Conclusion

Our findings suggest that GMI and mirror therapy may be effective for reducing PLP. However, this conclusion was drawn from a limited body of evidence, and the certainty of the evidence was very low. Therefore, rigorous, high-quality trials are needed to address the gap in the literature and inform practice.

Complex pattern of facial remapping in somatosensory cortex following congenital but not acquired hand loss

Cortical remapping after hand loss in the primary somatosensory cortex (S1) is thought to be predominantly dictated by cortical proximity, with adjacent body parts remapping into the deprived area. Traditionally, this remapping has been characterised by changes in the lip representation, which is assumed to be the immediate neighbour of the hand based on electrophysiological research in non-human primates. However, the orientation of facial somatotopy in humans is debated, with contrasting work reporting both an inverted and upright topography. We aimed to fill this gap in the S1 homunculus by investigating the topographic organisation of the face. Using both univariate and multivariate approaches we examined the extent of face-to-hand remapping in individuals with a congenital and acquired missing hand (hereafter one-handers and amputees, respectively), relative to two-handed controls. Participants were asked to move different facial parts (forehead, nose, lips, tongue) during functional MRI (fMRI) scanning. We first confirmed an upright face organisation in all three groups, with the upper-face and not the lips bordering the hand area. We further found little evidence for remapping of both forehead and lips in amputees, with no significant relationship to the chronicity of their phantom limb pain (PLP). In contrast, we found converging evidence for a complex pattern of face remapping in congenital one-handers across multiple facial parts, where relative to controls, the location of the cortical neighbour - the forehead - is shown to shift away from the deprived hand area, which is subsequently more activated by the lips and the tongue. Together, our findings demonstrate that the face representation in humans is highly plastic, but that this plasticity is restricted by the developmental stage of input deprivation, rather than cortical proximity.

Making sense of phantom limb pain

Phantom limb pain (PLP) impacts the majority of individuals who undergo limb amputation. The PLP experience is highly heterogenous in its quality, intensity, frequency and severity. This heterogeneity, combined with the low prevalence of amputation in the general population, has made it difficult to accumulate reliable data on PLP. Consequently, we lack consensus on PLP mechanisms, as well as effective treatment options. However, the wealth of new PLP research, over the past decade, provides a unique opportunity to re-evaluate some of the core assumptions underlying what we know about PLP and the rationale behind PLP treatments. The goal of this review is to help generate consensus in the field on how best to research PLP, from phenomenology to treatment. We highlight conceptual and methodological challenges in studying PLP, which have hindered progress on the topic and spawned disagreement in the field, and offer potential solutions to overcome these challenges. Our hope is that a constructive evaluation of the foundational knowledge underlying PLP research practices will enable more informed decisions when testing the efficacy of existing interventions and will guide the development of the next generation of PLP treatments.

Clinical Manifestations of Body Memories: The Impact of Past Bodily Experiences on Mental Health

Bodily experiences such as the feeling of touch, pain or inner signals of the body are deeply emotional and activate brain networks that mediate their perception and higher-order processing. While the ad hoc perception of bodily signals and their influence on behavior is empirically well studied, there is a knowledge gap on how we store and retrieve bodily experiences that we perceived in the past, and how this influences our everyday life. Here, we explore the hypothesis that negative body memories, that is, negative bodily experiences of the past that are stored in memory and influence behavior, contribute to the development of somatic manifestations of mental health problems including somatic symptoms, traumatic re-experiences or dissociative symptoms. By combining knowledge from the areas of cognitive neuroscience and clinical neuroscience with insights from psychotherapy, we identify Clinical Body Memory (CBM) mechanisms that specify how mental health problems could be driven by corporeal experiences stored in memory. The major argument is that the investigation of the neuronal mechanisms that underlie the storage and retrieval of body memories provides us with empirical access to reduce the negative impact of body memories on mental health.

Development and Validation of a Graded Motor Imagery Intervention for Phantom Limb Pain in Patients with Amputations (GraMI Protocol): A Delphi Study

BACKGROUND

Phantom limb pain can be defined as discomfort or pain in a missing part of the limb. The aims of this study were to develop and validate, through a Delphi methodology, a graded motor imagery protocol in order to reduce phantom limb pain.

METHOD

Physiotherapists and/or occupational therapists with experience in research and a minimum clinical experience of five years in the field of neurorehabilitation and/or pain were recruited by part of a group of experts to assess the intervention. The study was conducted through an online questionnaire, where experts assessed each aspect of the intervention through a Likert scale. As many rounds as necessary were carried out until consensus was reached among experts.

RESULTS

A total of two rounds were required to fully validate the intervention. During the second round, the relative interquartile range of all aspects to be assessed was less than 15%, thus showing a consensus among experts and with good concordance (Kappa index of 0.76).

CONCLUSION

Experts validated a graded motor imagery intervention of phantom limb pain in patients with amputations (GraMi protocol). This intervention can help to homogenize the use of graded motor imagery in future studies and in clinical practice.