Non-painful sensory phenomena after spinal cord injury

Maladaptive reorganization following SCI: The role of body representation and multisensory integration

In this review we focus on maladaptive brain reorganization after spinal cord injury (SCI), including the development of neuropathic pain, and its relationship with impairments in body representation and multisensory integration. We will discuss the implications of altered sensorimotor interactions after SCI with and without neuropathic pain and possible deficits in multisensory integration and body representation. Within this framework we will examine published research findings focused on the use of bodily illusions to manipulate multisensory body representation to induce analgesic effects in heterogeneous chronic pain populations and in SCI-related neuropathic pain. We propose that the development and intensification of neuropathic pain after SCI is partly dependent on brain reorganization associated with dysfunctional multisensory integration processes and distorted body representation. We conclude this review by suggesting future research avenues that may lead to a better understanding of the complex mechanisms underlying the sense of the body after SCI, with a focus on cortical changes.

Management of nonpainful supernumerary phantom limbs after incomplete spinal cord injury with visual-tactile feedback therapy: a case report

INTRODUCTION

Supernumerary phantom limb (SPL) is an uncommon phantom sensation where the patient experiences the illusory presence of one or more limbs in addition to their existing limbs. SPL after a spinal cord injury (SCI) is rare with few documented cases. There is minimal treatment guidance available, with some reports of visual-tactile feedback therapy used to manage SPL.

CASE PRESENTATION

A 43-year-old male sustained a C4 ASIA Impairment Scale grade C SCI, developing the sensation of two SPL arms originating from his shoulders 6 days after injury. He developed a self-directed method of visual-tactile feedback as a means to improve the SPL sensations, consisting of shrugging his shoulders repeatedly for 1 min while observing the movement of his actual arms. After completion of this routine, the SPL moved to the same location as his arms, providing relief. Also, an elastic band was placed on a sensate region of his arm, providing additional visual-tactile feedback. The SPL improved and resolved by day 45.

DISCUSSION

SPL after SCI is poorly characterized, usually occurring within 6-7 days of injury after a complete or incomplete cervical SCI. While the mechanism is unclear, the inability to integrate visual, tactile, and proprioceptive information after deafferentation may contribute to development. Similarities between SPL and phantom limb sensation after an amputation have resulted in the use of visual and visual-tactile feedback therapy for painful SPL management. This is the first case documenting successful use of visual-tactile feedback therapy to manage nonpainful SPL.

Influence of wheelchair user interface and personal characteristics on static and dynamic pretibial skin pressures in elite wheelchair racers, a pilot study

Context/objective: To examine personal (athletic classification, age, sex, body mass index, duration of disability, tactile sensation of lower extremities) and wheelchair (kneeling plate angle) factors associated with increased pretibial skin pressures in elite wheelchair racers.

Design: Cross-sectional study.

Setting: University-based laboratory in Champaign, USA.

Participants: A convenience sample of elite wheelchair races with traumatic spinal cord injury and spinal disease were recruited for participation.

Interventions: Interface pressure mapping was used to examine athletes' average and peak pretibial skin pressures in their own racing wheelchairs during static and dynamic (propulsive) conditions on a dynamometer.

Outcome measures: The study examined associations between personal and wheelchair factors and pressure, differences in pressure between static and dynamic conditions, and the influence of athletic classification (T53 vs. T54) on kneeling plate angle preference and skin pressure magnitudes.

Results: Increased kneeling plate angle was moderately associated with dynamic pressures. T53 athletes utilized more vertical kneeling angles and experienced larger average and peak pressures during propulsion. Duration of disability was negatively associated with all measures of pressure. Overall, mean dynamic peak pressure was significantly greater than mean static peak pressure.

Conclusion: This pilot study represents a first step in understanding the influence of user interface on potentially injurious skin pressures in wheelchair racers. Vertical kneeling plate configurations were associated with increased pressures while increased years with disability was associated with lower pretibial pressures. In addition, T53 athletes with less trunk function may be at a greater risk for experiencing larger interface pressures than T54 athletes.

Emerging Putative Associations between Non-Coding RNAs and Protein-Coding Genes in Neuropathic Pain: Added Value from Reusing Microarray Data

Regeneration of injured nerves is likely occurring in the peripheral nervous system, but not in the central nervous system. Although protein-coding gene expression has been assessed during nerve regeneration, little is currently known about the role of non-coding RNAs (ncRNAs). This leaves open questions about the potential effects of ncRNAs at transcriptome level. Due to the limited availability of human neuropathic pain (NP) data, we have identified the most comprehensive time-course gene expression profile referred to sciatic nerve (SN) injury and studied in a rat model using two neuronal tissues, namely dorsal root ganglion (DRG) and SN. We have developed a methodology to identify differentially expressed bioentities starting from microarray probes and repurposing them to annotate ncRNAs, while analyzing the expression profiles of protein-coding genes. The approach is designed to reuse microarray data and perform first profiling and then meta-analysis through three main steps. First, we used contextual analysis to identify what we considered putative or potential protein-coding targets for selected ncRNAs. Relevance was therefore assigned to differential expression of neighbor protein-coding genes, with neighborhood defined by a fixed genomic distance from long or antisense ncRNA loci, and of parental genes associated with pseudogenes. Second, connectivity among putative targets was used to build networks, in turn useful to conduct inference at interactomic scale. Last, network paths were annotated to assess relevance to NP. We found significant differential expression in long-intergenic ncRNAs (32 lincRNAs in SN and 8 in DRG), antisense RNA (31 asRNA in SN and 12 in DRG), and pseudogenes (456 in SN and 56 in DRG). In particular, contextual analysis centered on pseudogenes revealed some targets with known association to neurodegeneration and/or neurogenesis processes. While modules of the olfactory receptors were clearly identified in protein-protein interaction networks, other connectivity paths were identified between proteins already investigated in studies on disorders, such as Parkinson, Down syndrome, Huntington disease, and Alzheimer. Our findings suggest the importance of reusing gene expression data by meta-analysis approaches.

Plasticity and Awareness of Bodily Distortion

Knowledge of the body is filtered by perceptual information, recalibrated through predominantly innate stored information, and neurally mediated by direct sensory motor information. Despite multiple sources, the immediate prediction, construction, and evaluation of one's body are distorted. The origins of such distortions are unclear. In this review, we consider three possible sources of awareness that inform body distortion. First, the precision in the body metric may be based on the sight and positioning sense of a particular body segment. This view provides information on the dual nature of body representation, the reliability of a conscious body image, and implicit alterations in the metrics and positional correspondence of body parts. Second, body awareness may reflect an innate organizational experience of unity and continuity in the brain, with no strong isomorphism to body morphology. Third, body awareness may be based on efferent/afferent neural signals, suggesting that major body distortions may result from changes in neural sensorimotor experiences. All these views can be supported empirically, suggesting that body awareness is synthesized from multimodal integration and the temporal constancy of multiple body representations. For each of these views, we briefly discuss abnormalities and therapeutic strategies for correcting the bodily distortions in various clinical disorders.

Motor Cortex Stimulation for Pain Relief: Do Corollary Discharges Play a Role?

Both invasive and non-invasive motor cortex stimulation techniques have been successfully employed in the treatment of chronic pain, but the precise mechanism of action of such treatments is not fully understood. It has been hypothesized that a mismatch of normal interaction between motor intention and sensory feedback may result in central pain. Sensory feedback may come from peripheral nerves, vision and also from corollary discharges originating from the motor cortex itself. Therefore, a possible mechanism of action of motor cortex stimulation might be corollary discharge reinforcement, which could counterbalance sensory feedback deficiency. In other instances, primary deficiency in the production of corollary discharges by the motor cortex might be the culprit and stimulation of cortical motor areas might then be beneficial by enhancing production of such discharges. Here we review evidence for a possible role of motor cortex corollary discharges upon both the pathophysiology and the response to motor cortex stimulation of different types of chronic pain. We further suggest that the right dorsolateral prefrontal cortex (DLPC), thought to constantly monitor incongruity between corollary discharges, vision and proprioception, might be an interesting target for non-invasive neuromodulation in cases of chronic neuropathic pain.

The embodiment of assistive devices-from wheelchair to exoskeleton

Spinal cord injuries (SCIs) place a heavy burden on the healthcare system and have a high personal impact and marked socio-economic consequences. Clinically, no absolute cure for these conditions exists. However, in recent years, there has been an increased focus on new robotic technologies that can change the frame we think about the prognosis for recovery and for treating some functions of the body affected after SCIs. This review has two goals. The first is to assess the possibility of the embodiment of functional assistive tools after traumatic disruption of the neural pathways between the brain and the body. To this end, we will examine how altered sensorimotor information modulates the sense of the body in SCI. The second goal is to map the phenomenological experience of using external tools that typically extend the potential of the body physically impaired by SCI. More specifically, we will focus on the difference between the perception of one's physically augmented and non-augmented affected body based on observable and measurable behaviors. We discuss potential clinical benefits of enhanced embodiment of the external objects by way of multisensory interventions. This review argues that the future evolution of human robotic technologies will require adopting an embodied approach, taking advantage of brain plasticity to allow bionic limbs to be mapped within the neural circuits of physically impaired individuals.

Modulation of non-painful phantom sensation in subjects with spinal cord injury by means of rTMS

We aimed in this study to investigate whether repetitive transcranial magnetic stimulation (rTMS), given as theta burst stimulation (TBS), can interfere with non-painful phantom sensations in subjects with spinal cord injury (SCI). In double-blind, sham-controlled experiments in five subjects with cervical or thoracic traumatic SCI, we evaluated the effects of a single session of inhibitory (continuous) TBS, excitatory (intermittent) TBS, or placebo TBS, on simplex and complex non-painful phantom sensations. The interventions targeted the contralateral primary motor cortex (M1), the primary sensory cortex (S1) and the posterior parietal cortex (PPC). Measurements were carried out at baseline (T0), 5 min (T1) and 30 min later (T2) after the intervention. Descriptive evaluation of results shows that non-painful phantom sensations were not affected by rTMS applied over M1. Continuous (inhibitory) TBS over S1 induced a short-lasting decrease of simple non-painful phantom sensations, while continuous TBS over PPC induced a short-lasting decrease of both simple and complex phantom sensations. Intermittent (excitatory) TBS over PPC induced a slight increase of non-painful phantom sensations. Tests for significance confirm these observations, but must be interpreted with caution because of the small sample size. In conclusion, non-painful phantom sensations may be associated to a hyperexcitability of PPC and to a lesser extent of S1, which can be normalized by inhibitory rTMS. Our preliminary findings provide further evidence that neuromodulatory techniques are able to reverse phantom sensations not only after limb amputation but also in other conditions characterized by deafferentation such as SCI.

Illusory ownership of an invisible body reduces autonomic and subjective social anxiety responses

What is it like to be invisible? This question has long fascinated man and has been the central theme of many classic literary works. Recent advances in materials science suggest that invisibility cloaking of the human body may be possible in the not-so-distant future. However, it remains unknown how invisibility affects body perception and embodied cognition. To address these questions, we developed a perceptual illusion of having an entire invisible body. Through a series of experiments, we characterized the multisensory rules that govern the elicitation of the illusion and show that the experience of having an invisible body reduces the social anxiety response to standing in front of an audience. This study provides an experimental model of what it is like to be invisible and shows that this experience affects bodily self-perception and social cognition.

Invasive and non-invasive brain stimulation for treatment of neuropathic pain in patients with spinal cord injury: a review

CONTEXT

Past evidence has shown that invasive and non-invasive brain stimulation may be effective for relieving central pain.

OBJECTIVE

To perform a topical review of the literature on brain neurostimulation techniques in patients with chronic neuropathic pain due to traumatic spinal cord injury (SCI) and to assess the current evidence for their therapeutic efficacy.

METHODS

A MEDLINE search was performed using following terms: "Spinal cord injury", "Neuropathic pain", "Brain stimulation", "Deep brain stimulation" (DBS), "Motor cortex stimulation" (MCS), "Transcranial magnetic stimulation" (TMS), "Transcranial direct current stimulation" (tDCS), "Cranial electrotherapy stimulation" (CES).

RESULTS

Invasive neurostimulation therapies, in particular DBS and epidural MCS, have shown promise as treatments for neuropathic and phantom limb pain. However, the long-term efficacy of DBS is low, while MCS has a relatively higher potential with lesser complications that DBS. Among the non-invasive techniques, there is accumulating evidence that repetitive TMS can produce analgesic effects in healthy subjects undergoing laboratory-induced pain and in chronic pain conditions of various etiologies, at least partially and transiently. Another very safe technique of non-invasive brain stimulation - tDCS - applied over the sensory-motor cortex has been reported to decrease pain sensation and increase pain threshold in healthy subjects. CES has also proved to be effective in managing some types of pain, including neuropathic pain in subjects with SCI.

CONCLUSION

A number of studies have begun to use non-invasive neuromodulatory techniques therapeutically to relieve neuropathic pain and phantom phenomena in patients with SCI. However, further studies are warranted to corroborate the early findings and confirm different targets and stimulation paradigms. The utility of these protocols in combination with pharmacological approaches should also be explored.

Reorganization of the primary motor cortex of adult macaque monkeys after sensory loss resulting from partial spinal cord injuries

Long-term injuries to the dorsal columns of the spinal cord at cervical levels result in large-scale somatotopic reorganization of the somatosensory areas of the cortex and the ventroposterior nucleus of the thalamus. As a result of this reorganization, intact inputs from the face expand into the deafferented hand representations. Dorsal column injuries also result in permanent deficits in the use of digits for precision grip and a loss of fractionated movements of the digits. We determined whether the chronic loss of sensory inputs and the behavioral deficits caused by lesions of the dorsal columns in adult macaque monkeys affect organization of the motor cortex. The results show that, in the primary motor cortex, intracortical microstimulation evokes extension-flexion movements of the thumb at significantly fewer sites compared with the normal monkeys. There is a corresponding increase in the adduction-abduction movements. Furthermore, there is a significant increase in the thresholds of the currents required to evoke movements of the digits. Thus, long-term sensory loss in adult monkeys does not change the overall topography of the movement representation in the motor cortex but results in changes in the details of movement representations.

Comparison of LEP and QST and their contribution to standard sensory diagnostic assessment of spinal lesions: a pilot study

This study evaluates the additional use of laser-evoked potentials (LEP) and quantitative sensory testing (QST) in the sensory assessment of spinal lesions. Four consecutive patients with spinal lesions verified by MRI and clinical evidence for mild spinothalamic tract involvement were included. The electrophysiological workup [somatosensory evoked potentials (SEP) and LEP] was compared to QST. Electrophysiology and QST were reassessed after about 6 months. LEP detected impaired spinothalamic tract function in 7/8 examinations. QST pointed to spinothalamic tract lesions by loss of thermal function (3/8); most frequent positive sensory signs (3/8) were paradoxical heat sensations. LEP and QST results were concordant in 6/8 examinations. SEPs were abnormal in 2/8 examinations. Congruent results between SEP and both LEP and QST were obtained in 3/8 examinations. LEP detected more deficits than any single QST parameter or their combination but additional QST allows the detection of positive sensory signs. The diagnostic gain of SEP was limited.

Neuropathic pain in spinal cord injury: identification, classification, evaluation

OBJECTIVE

Chronic pain is very frequent after spinal cord injury, recent data showing that at least 80% of the patients experience pain, one-third at a severe level. The main objective of the present work is to report and discuss data regarding tools and procedures for the screening, diagnosis, and evaluation of neuropathic pain in spinal cord injury patients.

MATERIAL AND METHOD

The method used is that developed by the SOFMER, which associated a systematic review of the literature and a selection of published works by a scientific commitee, an analysis of data performed by a binom neuropathic pain/physical medicine and rehabilitation (PM&R) specialists, an evaluation of current practices during an expert consensus conference and via Internet, and finally a validation of the whole work by a pluridisciplinary expert panel.

RESULTS

The literature provides an important series of studies on pain in spinal injury, but without specific data about neuropathic pain in this population. Some specific diagnostic and evaluation tools for neuropathic pain have been developed these last years, while numerous classifications, based on various criteria, have been proposed, some of them exhibiting some advantages for a pragmatic application and being in parallel in accordance with recent nosological and physiopathological advances.

DISCUSSION

The DN4 questionnaire can be used for the screening and identification of neuropathic pain in this population of patients, often suffering from various types of pain. The use of the Spinal Cord Injury Pain Task Force of the International Association of the Study of Pain classification (SCIP-IASP), although some limitations, is recommended since taking into account physiopathology, localisation, and nature of pain. Daily uses of Visual Analogic Scale (VAS) or Numeric Scale (NS) are an obvious need and that of the questionnaire Douleur de Saint-Antoine (QDSA) for global evaluation and more specifically of the Neuropathic Pain Symptom Inventory (NPSI) for neuropathic pain are highly recommended.

Sensation of defecation in patients with spinal cord injury

STUDY DESIGN

For this study, a descriptive, explorative design was used.

OBJECTIVES

As a result of spinal cord injury (SCI) patients may have a partial or complete loss of the sensations of defecation. To compensate this impairment, nurses initiate bowel management programs. Therefore, they need information about sensations of defecation. Accordingly, the research questions explore which sensations of defecation are reported by patients with SCI and whether they can be used to improve bowel care.

SETTING

The Gemeinschaftskrankenhaus Herdecke and the Berufsgenossenschaftlichen Kliniken Bergmannsheil in Bochum, Germany.

METHODS

A convenience sample of 27 patients with SCI was interviewed using a semistructured questionnaire. For data analysis, the frequency of the reported sensations was counted.

RESULTS

The results of the study show that the participants' defecation was indicated by abdominal sensations (n=20) or a prickling sensation (n=11) emerging mainly in the head. Additional signals comprised increased spasticity (n=10), cutis anserina (n=8) and sweating (n=6). Seventeen participants sensed actual defecation and 15 perceived its cessation. Six participants were able to initiate defecating according to their sensations.

CONCLUSIONS

The assessment of sensations of defecation in patients with SCI may indicate whether a bowel-management program with a consistent schedule for defecation is needed or if physiological defecation can be trained.

Fire and phantoms after spinal cord injury: Na+ channels and central pain

Neuropathic pain and phantom phenomena occur commonly after spinal cord injury (SCI) but their molecular basis is not yet fully understood. Recent findings demonstrate abnormal expression of the Nav1.3 Na(+) channel within second-order spinal cord dorsal horn neurons and third-order thalamic neurons along the pain pathway after SCI, and suggest that this change makes these neurons hyperexcitable so that they act as pain amplifiers and generators. Delineation of molecular changes that contribute to hyperexcitability of pain-signaling neurons might lead to identification of molecular targets that will be useful in the treatment of neuropathic pain after SCI and related nervous system injuries.

Supernumerary phantoms: a comment on Grossi, et al.'s (2002) spare thoughts on spare limbs

A recently published case report of a supernumerary phantom limb in a man with left-sided hemiplegia did not take note that this phenomenon has been extensively documented in the neurological literature for well over 100 years. The present comment provides a brief introduction to the clinical and experimental approaches to supernumerary phantom limbs. It also emphasizes the theoretical importance of this condition for understanding the neurological mechanisms subserving the experience of having a body.

Psychosocial Profiles of People With Pain Associated With Spinal Cord Injury

OBJECTIVES

The objectives of the study were to: (1) identify psychosocial profiles of people with pain associated with spinal cord injuries (SCI), and (2) compare the psychosocial profiles with other chronic pain syndromes.

METHODS

History questionnaires and the Multidimensional Pain Inventory (MPI) were mailed to 159 persons with chronic pain and SCIs (SCICP) and 120 (75.5%) agreed to participate.

RESULTS

Cluster analysis of MPI scores identified 2 subgroups of SCICP. One (42.5%) was characterized by high Pain Severity (PS), Affective Distress (AD), Life Interference (LI), and low Life Control (LC) similar to a previously identified cluster labeled Dysfunctional. The second (57.5%) was characterized by low PS, AD, LI, and high levels of LC and activity (GA), similar to the Adaptive Copers (AC) cluster identified in previous studies with the exception that the scores were lower on Support (S), Solicitous Responses (SR), and Negative Responses (NR) and higher on Distracting Responses (DR). Both subgroups were similar to those observed in other chronic pain syndromes (CPSs). People with SCIs differed significantly from heterogeneous chronic pain and chronic headaches in that they indicated less inference of pain with activities. They also scored lower on S. SCICP reported comparable levels of LI, LC, AD, S, SR, but greater levels of PS compared with a group of people with post-polio syndrome.

DISCUSSION

The similarities and differences between SCI and other CPSs suggest that although a general measure assessing psychosocial impact can be used across pain syndromes, it is important to use different norms for comparison of particular pain syndromes. The failure to identify a subgroup of patients characterized by low levels of S and high levels of NR, and the low SR and DR for SCICP compared with other CPSs warrants examination.

Chronic pain and nonpainful sensations after spinal cord injury: is there a relation?

OBJECTIVES

First, to define the clinical characteristics of nonpainful sensations (NP) that commonly appear after spinal cord injury (SCI); and second, to compare the clinical characteristics of NP and chronic pain (CP) after SCI.

METHODS

Two sets of questions concerning CP and NP were mailed to 330 subjects. Responses from 197 persons experiencing CP as well as NP were analyzed.

RESULTS

The most common locations for CP and NP were back and lower extremities. Although the number of areas in which the subjects perceived CP and NP to be located was significantly correlated, a factor analysis showed separate groupings of areas with CP and NP, respectively. Self-reported allodynia or hyperesthesia in the lower extremities, however, was significantly associated with CP in the same areas. The number of descriptive adjectives used for CP and NP was also significantly correlated, as was the perceived intensity of CP versus NP. Additionally, significant correlations were found in onset and temporal pattern of CP and NP. Similarly to CP, NP interfered with sleep, work, and other daily activities, and the patterns of interference due to CP and NP were significantly correlated.

DISCUSSION

While many aspects of the clinical picture of CP and NP are similar after SCI, the CP and spontaneous NP are not necessarily located in the same areas. Although the observed similarities between CP and NP may be based on pathophysiologic mechanisms, the significant relations between the interference patterns suggest that psychosocial mechanisms related to coping are also involved.

Vestibular caloric stimulation evokes phantom limb illusions in patients with paraplegia

STUDY DESIGN

Prospective study.

OBJECTIVES

To determine the mechanisms of body illusions in paraplegia patients as compared with the amputee phantom phenomena.

METHODS

A vestibular caloric stimulation was performed in 10 consecutive patients with complete section of the spinal cord. Perception of body, before and after stimulation, was classed as illusion of a normal body (lower limbs with normal morphological, postural and kinetic characteristics perceived as before spinal injury), normal phantom (overly vivid perception of all or part of the lower limbs), deformed phantom (perception of all or part of the limbs below the injury level as abnormal in shape, posture, movement or even number), or painful phantom.

RESULTS

After vestibular caloric stimulation, nine out of 10 patients stated their perception of body segments below the injury level had changed to normal phantoms or to deformed phantoms (morphological, postural or kinetic changes). Among the four patients who initially had painful limbs, two stated the stimulation greatly relieved their pain.

CONCLUSION

The normal or deformed phantom evoked by vestibular stimulation would result from use of identity data or instantaneous data as is observed in amputees. Cerebral remapping following deafferentation could be the origin of the deformed phantoms. Illusions corresponding to phenomena perceived at the time of the accident corresponding to autobiographical engrammes do not appear to be evoked by vestibular stimulation, as is also the case in amputees.