Evaluating peripheral neuromuscular function with brief movement-evoked pain

Movement-evoked pain is an understudied manifestation of musculoskeletal conditions that contributes to disability, yet little is known about how the neuromuscular system responds to movement-evoked pain. The present study examined whether movement-evoked pain impacts force production, electromyographic (EMG) muscle activity, and the rate of force development (RFD) during submaximal muscle contractions. Fifteen healthy adults (9 males; age = 30.3 ± 10.2 yr, range = 22-59 yr) performed submaximal isometric first finger abduction contractions without pain (baseline) and with movement-evoked pain induced by laser stimulation to the dorsum of the hand. Normalized force (% maximal voluntary contraction) and RFD decreased by 11% (P < 0.001) and 15% (P = 0.003), respectively, with movement-evoked pain, without any change in normalized peak EMG (P = 0.77). Early contractile RFD, force impulse, and corresponding EMG amplitude computed within time segments of 50, 100, 150, and 200 ms relative to the onset of movement were also unaffected by movement-evoked pain (P > 0.05). Our results demonstrate that movement-evoked pain impairs peak characteristics and not early measures of submaximal force production and RFD, without affecting EMG activity (peak and early). Possible explanations for the stability in EMG with reduced force include antagonist coactivation and a reorganization of motoneuronal activation strategy, which is discussed here.NEW & NOTEWORTHY We provide neurophysiological evidence to indicate that peak force and rate of force development are reduced by movement-evoked pain despite a lack of change in EMG and early rapid force development in the first dorsal interosseous muscle. Additional evidence suggests that these findings may coexist with a reorganization in motoneuronal activation strategy.

Central neuropathic pain

Central neuropathic pain arises from a lesion or disease of the central somatosensory nervous system such as brain injury, spinal cord injury, stroke, multiple sclerosis or related neuroinflammatory conditions. The incidence of central neuropathic pain differs based on its underlying cause. Individuals with spinal cord injury are at the highest risk; however, central post-stroke pain is the most prevalent form of central neuropathic pain worldwide. The mechanisms that underlie central neuropathic pain are not fully understood, but the pathophysiology likely involves intricate interactions and maladaptive plasticity within spinal circuits and brain circuits associated with nociception and antinociception coupled with neuronal hyperexcitability. Modulation of neuronal activity, neuron-glia and neuro-immune interactions and targeting pain-related alterations in brain connectivity, represent potential therapeutic approaches. Current evidence-based pharmacological treatments include antidepressants and gabapentinoids as first-line options. Non-pharmacological pain management options include self-management strategies, exercise and neuromodulation. A comprehensive pain history and clinical examination form the foundation of central neuropathic pain classification, identification of potential risk factors and stratification of patients for clinical trials. Advanced neurophysiological and neuroimaging techniques hold promise to improve the understanding of mechanisms that underlie central neuropathic pain and as predictive biomarkers of treatment outcome.

Race-based reporting and participation of Black individuals in registered pain clinical trials, United States, 2000 to 2019

ABSTRACT

There are numerous, well-established racial disparities in the management of pain. The degree to which these are evident at the stage of conducting clinical trials is unknown. To address this knowledge gap, we examined race-based reporting, participation of Black individuals, and the factors associated with reporting and participation in pain clinical trials in the United States. Data were extracted from Clinicaltrials.gov and published articles. One thousand two hundred trials met our inclusion criteria; 482 (40.2%) reported participant race. More recent, publicly funded, and larger trials were more likely to report race. Of 82,468 participants included in pain clinical trials that reported race, 15,101 were Black individuals (18.3%). Participation of Black individuals was significantly associated with pain type (ß = +27% in cardiovascular disease pain compared with acute pain, P < 0.05), study population (ß = +33% and +7% in pain in minoritized populations and women, respectively, compared with general population, P < 0.05), pain intervention (ß = +7.5% for trials of opioid interventions compared with nonopioid interventions, P < 0.05), and a diverse team of investigators (ß = +8.0% for studies incorporating a visible non-White investigator compared with those that did not, P < 0.05). Our results indicate that representation of Black participants in pain clinical trials generally aligns with national demographics in the United States. Increased representation corresponds with health conditions more prevalent among Black individuals (eg, cardiovascular disease) and with a diverse study team composition. Despite these encouraging results, less than half of pain trials reported race, which introduces potential publication bias and limits external validity.

Physical pain among Indigenous Peoples in Canada: a scoping review

PURPOSE

Pain is a multifaceted experience shaped by various factors including context of pain, previous life events, and ongoing ethnocultural circumstances. Moreover, the definition of pain is inconsistent across cultures. Western medicine views physical pain (e.g., associated with a bone fracture) and nonphysical mental pain (e.g., depression) as two distinct conditions. Indigenous perspectives are often more wholistic, encompassing mental, spiritual, emotional, and physical hurt. The subjective nature of pain invites ample opportunity for discrimination in both its assessment and management. As such, it is important to consider Indigenous perspectives of pain in research and clinical practice. To investigate which aspects of Indigenous pain knowledge are currently considered by Western research, we conducted a scoping review of the literature on pain in Indigenous Peoples of Canada.

SOURCE

In June 2021, we searched nine databases and downloaded 8,220 papers after removal of duplicates. Two independent reviewers screened abstracts and full-text articles.

PRINCIPLE FINDINGS

Seventy-seven papers were included in the analysis. Using grounded theory, five themes emerged: pain measures/scales (n = 7), interventions (n = 13), pharmaceuticals (n = 17), pain expression/experiences (n = 45), and pain conditions (n = 70).

CONCLUSION

This scoping review shows that there is a paucity of research on pain measurement in Indigenous Peoples of Canada. This finding is concerning in light of numerous studies reporting that Indigenous Peoples experience their pain as ignored, minimized, or disbelieved. Furthermore, a clear disconnect emerged between pain expression in Indigenous Peoples and assessment in medical professionals. We hope that this scoping review will serve to translate current knowledge to other non-Indigenous academics and to initiate meaningful collaboration with Indigenous partners. Future research led by Indigenous academics and community partners is critically needed to better address pain needs in Canada.

Pharmacological management of acute spinal cord injury: a longitudinal multi-cohort observational study

Multiple types and classes of medications are administered in the acute management of traumatic spinal cord injury. Prior clinical studies and evidence from animal models suggest that several of these medications could modify (i.e., enhance or impede) neurological recovery. We aimed to systematically determine the types of medications commonly administered, alone or in combination, in the transition from acute to subacute spinal cord injury. For that purpose, type, class, dosage, timing, and reason for administration were extracted from two large spinal cord injury datasets. Descriptive statistics were used to describe the medications administered within the first 60 days after spinal cord injury. Across 2040 individuals with spinal cord injury, 775 unique medications were administered within the two months after injury. On average, patients enrolled in a clinical trial were administered 9.9 ± 4.9 (range 0-34), 14.3 ± 6.3 (range 1-40), 18.6 ± 8.2 (range 0-58), and 21.5 ± 9.7 (range 0-59) medications within the first 7, 14, 30, and 60 days post-injury, respectively. Those enrolled in an observational study were administered on average 1.7 ± 1.7 (range 0-11), 3.7 ± 3.7 (range 0-24), 8.5 ± 6.3 (range 0-42), and 13.5 ± 8.3 (range 0-52) medications within the first 7, 14, 30, and 60 days post-injury, respectively. Polypharmacy was commonplace (up to 43 medications per day per patient). Approximately 10% of medications were administered acutely as prophylaxis (e.g., against the development of pain or infections). To our knowledge, this was the first time acute pharmacological practices have been comprehensively examined after spinal cord injury. Our study revealed a high degree of polypharmacy in the acute stages of spinal cord injury, raising the potential to impact neurological recovery. All results can be interactively explored on the R_XSCI web site ( https://jutzelec.shinyapps.io/RxSCI/ ) and GitHub repository ( https://github.com/jutzca/Acute-Pharmacological-Treatment-in-SCI/ ).

Pain-related gamma band activity is dependent on the features of nociceptive stimuli: a comparison of laser and contact heat

Painful contact heat and laser stimulation offer an avenue to characterize nociceptive pathways involved in acute pain processing, by way of evoked potentials. Direct comparisons of radiant laser and contact heat are limited, particularly in context of examining time-frequency responses to stimulation. This is important in light of recent evidence to suggest that gamma band oscillations (GBOs) represent a functionally heterogeneous measure of pain. The purpose of the current study was to investigate differences in GBOs generated in response to laser and contact heat stimulation of the nondominant forearm. Following intensity matching to pain ratings, evoked electroencephalography (EEG) responses to laser and contact heat stimulation were examined in the time-frequency domain in the same participants (19 healthy adults) across two sessions. At ∼200 ms, both contact heat and laser stimulation resulted in significant, group-level event-related synchronization (ERS) in the low gamma band (i.e., 30-60 Hz) in central electrode locations (Cc, Cz, Ci). Laser stimulation also generated ERS in the 60-100 Hz range (i.e., high gamma), at ∼200 ms, while contact heat led to a significant period of desynchronization in the high gamma range between 400 and 600 ms. Both contact heat and laser GBOs were stronger on the central electrodes contralateral to the stimulated forearm, indicative of primary somatosensory cortex involvement. Based on our findings, and taken in conjunction with previous studies, laser and contact heat stimulation generate characteristically different responses in the brain, with only the former leading to high-frequency GBOs characteristic of painful stimuli.NEW & NOTEWORTHY Despite matching pain perception between noxious laser and contact heat stimuli, we report notable differences in gamma band oscillations (GBO), measured via electroencephalography. GBOs produced following contact heat more closely resembled that of nonnoxious stimuli, while GBOs following laser stimuli were in line with previous reports. Taken together, laser and contact heat stimulation generate characteristically different responses in the brain, with only the former leading to high-frequency GBOs characteristic of painful stimuli.

Systemic Immune Profile Predicts the Development of Infections in Patients with Spinal Cord Injuries

Patients with spinal cord injury (SCI) frequently develop infections that may affect quality of life, be life-threatening, and impair their neurological recovery in the acute and subacute injury phases. Therefore, identifying patients with SCI at risk for developing infections in this stage is of utmost importance. We determined the systemic levels of immune cell populations, cytokines, chemokines, and growth factors in 81 patients with traumatic SCI at 4 weeks after injury and compared them with those of 26 age-matched healthy control subjects. Patients who developed infections between 4 and 16 weeks after injury exhibited higher numbers of neutrophils and eosinophils, as well as lower numbers of lymphocytes and eotaxin-1 (CCL11) levels. Accordingly, lasso logistic regression showed that incomplete lesions (American Spinal Injury Association Impairment Scale [AIS] C and D grades), the levels of eotaxin-1, and the number of lymphocytes, basophils, and monocytes are predictive of lower odds for infections. On the other hand, the number of neutrophils and eosinophils as well as, in a lesser extent, the levels of IP-10 (CXCL10), MCP-1 (CCL2), BDNF [brain-derived neurotrophic factor], and vascular endothelial growth factor [VEGF]-A, are predictors of increased susceptibility for developing infections. Overall, our results point to systemic immune disbalance after SCI as predictors of infection in a period when infections may greatly interfere with neurological and functional recovery and suggest new pathways and players to further explore novel therapeutic strategies.

Supraspinal facilitation to repetitive painful stimulation: A laser evoked potential study

To better characterize central modulation mechanisms involved in the processing of daily repetitive painful stimulation, laser evoked potentials were recorded at and away from the conditioning area in healthy participants. In addition, we aimed to evaluate a repetitive painful stimulation paradigm that could be conducted in a shorter time frame than previous studies. Collectively, continuous pain rating, warm and heat pain threshold results suggest that sensitivity to pain was reduced 24 hours after the shortened repeated painful stimulation. Laser evoked potentials revealed a significant increase in the contralateral arm to where the conditioning stimulus was applied. This finding was specific to noxious conditioning (i.e., not seen in the control brush experiment). These results provide neurophysiological evidence of pain facilitation resulting from prolonged exposure to painful heat, potentially arising in supraspinal structures.

Current trends and outcomes of non-elective neurosurgical care in Central Europe during the second year of the COVID-19 pandemic

Reflecting the first wave COVID-19 pandemic in Central Europe (i.e. March 16th–April 15th, 2020) the neurosurgical community witnessed a general diminution in the incidence of emergency neurosurgical cases, which was impelled by a reduced number of traumatic brain injuries (TBI), spine conditions, and chronic subdural hematomas (CSDH). This appeared to be associated with restrictions imposed on mobility within countries but also to possible delayed patient introduction and interdisciplinary medical counseling. In response to one year of COVID-19 experience, also mapping the third wave of COVID-19 in 2021 (i.e. March 16 to April 15, 2021), we aimed to reevaluate the current prevalence and outcomes for emergency non-elective neurosurgical cases in COVID-19-negative patients across Austria and the Czech Republic. The primary analysis was focused on incidence and 30-day mortality in emergency neurosurgical cases compared to four preceding years (2017–2020). A total of 5077 neurosurgical emergency cases were reviewed. The year 2021 compared to the years 2017–2019 was not significantly related to any increased odds of 30 day mortality in Austria or in the Czech Republic. Recently, there was a significant propensity toward increased incidence rates of emergency non-elective neurosurgical cases during the third COVID-19 pandemic wave in Austria, driven by their lower incidence during the first COVID-19 wave in 2020. Selected neurosurgical conditions commonly associated with traumatic etiologies including TBI, and CSDH roughly reverted to similar incidence rates from the previous non-COVID-19 years. Further resisting the major deleterious effects of the continuing COVID-19 pandemic, it is edifying to notice that the neurosurgical community´s demeanor to the recent third pandemic culmination keeps the very high standards of non-elective neurosurgical care alongside with low periprocedural morbidity. This also reflects the current state of health care quality in the Czech Republic and Austria.

Quality of meta-analyses of non-opioid, pharmacological, perioperative interventions for chronic postsurgical pain: a systematic review

Background

In an attempt to aggregate observations from clinical trials, several meta-analyses have been published examining the effectiveness of systemic, non-opioid, pharmacological interventions to reduce the incidence of chronic postsurgical pain.

Objective

To inform the design and reporting of future studies, the purpose of our study was to examine the quality of these meta-analyses.

Evidence review

We conducted an electronic literature search in Embase, MEDLINE, and the Cochrane Database of Systematic Reviews. Published meta-analyses, from the years 2010 to 2020, examining the effect of perioperative, systemic, non-opioid pharmacological treatments on the incidence of chronic postsurgical pain in adult patients were identified. Data extraction focused on methodological details. Meta-analysis quality was assessed using the A Measurement Tool to Assess Systematic Reviews 2 (AMSTAR 2) critical appraisal tool.

Findings

Our search yielded 17 published studies conducting 58 meta-analyses for gabapentinoids (gabapentin and pregabalin), ketamine, lidocaine, non-steroidal anti-inflammatory drugs, and mexiletine. According to AMSTAR 2, 88.2% of studies (or 15/17) were low or critically low in quality. The most common critical element missing was an analysis of publication bias. Trends indicated an improvement in quality over time and association with journal impact factor.

Conclusions

With few individual trials adequately powered to detect treatment effects, meta-analyses play a crucial role in informing the perioperative management of chronic postsurgical pain. In light of this inherent value and despite a number of attempts, high-quality meta-analyses are still needed.

PROSPERO registration number

CRD42021230941.

The Influence of Examiner Gender on Responses to Tonic Heat Pain Assessments: A Preliminary Investigation

Background: The influence of examiner gender on pain reporting has been previously explored in both research and clinical settings. However, previous investigations have been limited, with the majority of studies employing single, static assessments of pain (e.g., cold pressor test, verbal pain ratings). The impact of examiner gender on both static and dynamic heat-based pain assessments is currently unknown.

Methods: Thirty eight participants (20 females aged 24.1 ± 4.44, and 18 males, aged 24.8 ± 4.54) completed two identical testing sessions, randomized to a male and female examiner in a cross-over design. Pain sensitivity was examined using heat pain thresholds, verbal pain ratings to tonic heat, computerized visual analog scale (CoVAS) rating to tonic heat, and participant-controlled temperature (PCT) heat pain assessments.

Results: Female participants reported higher verbal pain to tonic heat with a female examiner compared to male participants, with similar trends for CoVAS responses to tonic heat. Conversely heat pain thresholds and PCT were not significantly influenced by experimenter gender.

Conclusions: Overall, verbal ratings were the most impacted by examiner gender, with temperature-based methods such as PCT and pain thresholds showing little to no examiner gender effects. While the gender of the examiner may be an important consideration in the measurement of sex and gender differences in pain research, the choice of pain assessment method may be of similar consequence.

Efficacy of topical cannabinoids in the management of pain: a systematic review and meta-analysis of animal studies

BACKGROUND/IMPORTANCE

Cannabinoids are emerging as an alternative pain management option, preliminarily supported by preclinical and clinical studies. Unwanted side effects from oral or inhaled cannabinoids remain, however, a major barrier to widespread use. Peripherally acting cannabinoids (eg, topically applied) may circumvent these side effects while providing localized pain management.

OBJECTIVE

Our purpose was to systematically review the literature on the effectiveness of peripherally acting cannabinoids for pain management.

EVIDENCE REVIEW

We searched MEDLINE, EMBASE, CENTRAL, CINAHL, and PubMed databases. Included studies examined the effect of topical/peripherally administered cannabinoids on pain ratings in humans, as well as pain-related outcomes in animals (eg, paw withdrawal). Due to a lack of trials, human studies were summarized in a narrative synthesis. Separate meta-analyses were performed for animal studies using radiant tail flick or paw withdrawal outcomes.

FINDINGS

Our search yielded 1182 studies following removal of duplicates, with 46 studies (6 human, 40 animal) included. Human studies (one randomized controlled trial and five case studies/series) reported no adverse events to topical cannabinoids and preliminary evidence of decreased pain ratings. Animal studies reporting tail flick (5) (2.81, 95% CI 1.93 to 3.69, p<0.001) and mechanical withdrawal (11) (2.74, 95% CI 1.82 to 3.67, p<0.001) reported prolonged responses (analgesia) in peripheral cannabinoid groups compared with controls.

CONCLUSIONS

Preclinical animal studies provided low-quality evidence for peripherally administered cannabinoids to provide regional, antinociceptive effects. The scarcity of high-quality human studies underscores the need to translate preclinical evidence into well-controlled human trials.

A NEW SCORE BASED ON THE INTERNATIONAL STANDARDS FOR NEUROLOGICAL CLASSIFICATION OF SPINAL CORD INJURY FOR INTEGRATIVE EVALUATION OF CHANGES IN SENSORIMOTOR FUNCTIONS

Sensorimotor function of patients with spinal cord injury (SCI) is commonly assessed according to the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI). From the ISNCSCI segmental motor and sensory assessments, upper and lower extremity motor scores (UEMS and LEMS), sum scores of pin prick (PP) and light touch (LT) sensation, the neurological level of injury (NLI) and the classification of lesion severity according to the American Spinal Injury Association Impairment Scale (AIS) grade are derived. Changes of these parameters over time are widely used to evaluate neurological recovery. However, evaluating recovery based on a single ISNCSCI scoring or classification variable may misestimate overall recovery. Here, we propose an Integrated Neurological Change Score (INCS) based on the combination of normalized changes between two-time points of UEMS, LEMS, and total PP and LT scores. To assess the agreement of INCS with clinical judgement of meaningfulness of neurological changes, changes of ISNCSCI variables between two time-points of 88 patients from an independent cohort were rated by 20 clinical experts according to a 5-categories Likert Scale. As for individual ISNCSCI variables, neurological change measured by INCS is associated to severity (AIS grade), age and time since injury, but INCS better reflects clinical judgment about meaningfulness of neurological changes than individual ISNCSCI variables. In addition, INCS is related with changes in functional independence measured by the Spinal Cord Independence Measure (SCIM) in patients with tetraplegia. INCS may be a useful measure of overall neurological change in clinical studies.

Can Magnetic Resonance Imaging Reveal Lower Motor Neuron Damage after Traumatic Spinal Cord Injury? A Scoping Review

Restoring muscle function to patients with spinal cord injuries (SCIs) will invariably require a functioning lower motor neuron (LMN). As techniques such as nerve transfer surgery emerge, characterizing the extent of LMN damage associated with SCIs becomes clinically important. Current methods of LMN diagnosis have inherent limitations that could potentially be overcome by the development of magnetic resonance imaging (MRI) biomarkers: specific features on MRI that are indicative of LMN integrity. To identify research on MRI biomarkers of LMN damage in the acute phase after SCI, we searched PubMed, EMBASE, MEDLINE, and the Cochrane Central Register of Controlled Trials for articles published from inception to April 27, 2021. Overall, 2 of 58 unique articles screened met our inclusion criteria, both of which were small studies. We therefore identify MRI biomarkers of LMN damage overlying SCI as a notable gap in the literature. Because of the lack of existing literature on this specific problem, we further our discussion by examining concepts explored in research characterizing MRI biomarkers of spinal cord and neuronal damage in different contexts that may provide value in future work to identify a biomarker for LMN damage in SCI. We conclude that MRI biomarkers of LMN damage in SCI is an underexplored, but promising, area of research as emerging, function-restoring therapies requiring this information continue to advance.

Eccentric rehabilitation induces white matter plasticity and sensorimotor recovery in chronic spinal cord injury

Experience-dependent white matter plasticity offers new potential for rehabilitation-induced recovery after neurotrauma. This first-in-human translational experiment combined myelin water imaging in humans and genetic fate-mapping of oligodendrocyte lineage cells in mice to investigate whether downhill locomotor rehabilitation that emphasizes eccentric muscle actions promotes white matter plasticity and recovery in chronic, incomplete spinal cord injury (SCI). In humans, of 20 individuals with SCI that enrolled, four passed the imaging screen and had myelin water imaging before and after a 12-week (3 times/week) downhill locomotor treadmill training program (SCI + DH). One individual was excluded for imaging artifacts. Uninjured control participants (n = 7) had two myelin water imaging sessions within the same day. Changes in myelin water fraction (MWF), a histopathologically-validated myelin biomarker, were analyzed in a priori motor learning and non-motor learning brain regions and the cervical spinal cord using statistical approaches appropriate for small sample sizes. PDGFRα-CreER^T2:mT/mG mice, that express green fluorescent protein on oligodendrocyte precursor cells and subsequent newly-differentiated oligodendrocytes upon tamoxifen-induced recombination, were either naive (n = 6) or received a moderate (75 kilodyne), contusive SCI at T9 and were randomized to downhill training (n = 6) or unexercised groups (n = 6). We initiated recombination 29 days post-injury, seven days prior to downhill training. Mice underwent two weeks of daily downhill training on the same 10% decline grade used in humans. Between-group comparison of functional (motor and sensory) and histological (oligodendrogenesis, oligodendroglial/axon interaction, paranodal structure) outcomes occurred post-training. In humans with SCI, downhill training increased MWF in brain motor learning regions (postcentral, precuneus) and mixed motor and sensory tracts of the ventral cervical spinal cord compared to control participants (P < 0.05). In mice with thoracic SCI, downhill training induced oligodendrogenesis in cervical dorsal and lateral white matter, increased axon-oligodendroglial interactions, and normalized paranodal structure in dorsal column sensory tracts (P < 0.05). Downhill training improved sensorimotor recovery in mice by normalizing hip and knee motor control and reducing hyperalgesia, both of which were associated with new oligodendrocytes in the cervical dorsal columns (P < 0.05). Our findings indicate that eccentric-focused, downhill rehabilitation promotes white matter plasticity and improved function in chronic SCI, likely via oligodendrogenesis in nervous system regions activated by the training paradigm. Together, these data reveal an exciting role for eccentric training in white matter plasticity and sensorimotor recovery after SCI.

The Impact of Sub-maximal Exercise on Neuropathic Pain, Inflammation, and Affect Among Adults With Spinal Cord Injury: A Pilot Study

Introduction: Persons with spinal cord injury (SCI) often report high levels of neuropathic pain (NP) and poor well-being, which may result from increased inflammation. This study examined the impact of sub-maximal aerobic exercise on NP, inflammation and psychological affect among adults with SCI. Methods: Eight active adults with tetraplegia (n-4, AIS A-C) and paraplegia (n = 4, AIS A-C) performed 30-min of arm-crank aerobic exercise and reported their ratings of perceived exertion (RPE) each minute. Measures of NP, affect, and inflammatory cytokines (IL-6, IL-10, IL-1ra, TNF-α) were taken pre-(T₀), immediately post-(T₁), and 90-min post-exercise (T₂). Results: NP decreased between T₀ and T₁ for tetraplegics (-60%, d = 0.47; CI = -0.32, 2.02) and paraplegics (-16%, d = 0.15; CI = -0.30, 0.90). Correlations between change in cytokines and change in NP were medium-to large for tetraplegics (rs ranged from -0.820 to 0.965) and paraplegics (rs ranged from -0.598 to 0.833). However, the pattern of correlations between change in cytokines and affect was inconsistent between groups. Lower baseline levels of IL-1ra predicted greater decreases in NP immediately post-exercise (r = 0.83, p = 0.01). Conclusion: Sub-maximal exercise can positively impact NP for some persons with SCI. Further experimental research should identify the optimal exercise intensity to reduce NP for persons with SCI, in addition to understanding biomarkers which may predict changes in NP. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT03955523.

A data-driven T2 relaxation analysis approach for myelin water imaging: Spectrum analysis for multiple exponentials via experimental condition oriented simulation (SAME-ECOS)

PURPOSE

The decomposition of multi-exponential decay data into a T₂ spectrum poses substantial challenges for conventional fitting algorithms, including non-negative least squares (NNLS). Based on a combination of the resolution limit constraint and machine learning neural network algorithm, a data-driven and highly tailorable analysis method named spectrum analysis for multiple exponentials via experimental condition oriented simulation (SAME-ECOS) was proposed.

THEORY AND METHODS

The theory of SAME-ECOS was derived. Then, a paradigm was presented to demonstrate the SAME-ECOS workflow, consisting of a series of calculation, simulation, and model training operations. The performance of the trained SAME-ECOS model was evaluated using simulations and six in vivo brain datasets. The code is available at https://github.com/hanwencat/SAME-ECOS.

RESULTS

Using NNLS as the baseline, SAME-ECOS achieved over 15% higher overall cosine similarity scores in producing the T₂ spectrum, and more than 10% lower mean absolute error in calculating the myelin water fraction (MWF), as well as demonstrated better robustness to noise in the simulation tests. Applying to in vivo data, MWF from SAME-ECOS and NNLS was highly correlated among all study participants. However, a distinct separation of the myelin water peak and the intra/extra-cellular water peak was only observed in the mean T₂ spectra determined using SAME-ECOS. In terms of data processing speed, SAME-ECOS is approximately 30 times faster than NNLS, achieving a whole-brain analysis in 3 min.

CONCLUSION

Compared with NNLS, the SAME-ECOS method yields much more reliable T₂ spectra in a dramatically shorter time, increasing the feasibility of multi-component T₂ decay analysis in clinical settings.

A Systematic Review of Safety Reporting in Acute Spinal Cord Injury Clinical Trials: Challenges and Recommendations

Accurate safety information in published clinical trials guides the assessment of risk-benefit, as well as the design of future clinical trials. Comprehensive reporting of adverse events, toxicity, and discontinuations from acute spinal cord injury clinical trials is an essential step in this process. Here, we sought to assess the degree of "satisfactoriness" of reporting in past clinical trials in spinal cord injury. A review of citations from MEDLINE and EMBASE identified eligible clinical trials in acute (within 30 days) spinal cord injury. English language studies, published between 1980 and 2020, with sensory, motor, or autonomic neurological assessments as the primary outcome measure were eligible for inclusion. Criteria were then established to qualify the safety reporting as satisfactory (i.e., distinguished severe/life-threatening events), partially satisfactory, or unsatisfactory (i.e., only mentioned in general statements, or reported but without distinguishing severe events). A total of 40 trials were included. Satisfactory reporting for clinical adverse events was observed in 30% of trials; partially satisfactory was achieved by 10% of the trials, and the remaining 60% were unsatisfactory. The majority of trials were determined to be unsatisfactory for the reporting of laboratory-defined toxicity (82.5%); only 17.5% were satisfactory. Discontinuations were satisfactorily reported for the majority of trials (80%), with the remaining partially satisfactory (5%) or unsatisfactory (15%). Reporting of safety in clinical trials for acute spinal cord injury is suboptimal. Due to the complexities of acute spinal cord injury (e.g., polytrauma, multiple systems affected), tailored and specific standards for tracking adverse events and safety reporting should be established.

Characterization of Hyperacute Neuropathic Pain after Spinal Cord Injury: A Prospective Study

There is currently a lack of information regarding neuropathic pain in the very early stages of spinal cord injury (SCI). In the present study, neuropathic pain was assessed using the Douleur Neuropathique 4 Questions (DN4) for the patient's worst pain within the first 5 days of injury (i.e., hyperacute) and on follow-up at 3, 6, and 12 months. Within the hyperacute time frame (i.e., 5 days), at- and below-level neuropathic pain were reported as the worst pain in 23% (n = 18) and 5% (n = 4) of individuals with SCI, respectively. Compared to the neuropathic pain observed in this hyperacute setting, late presenting neuropathic pain was characterized by more intense painful electrical and cold sensations, but less itching sensations. Phenotypic differences between acute and late neuropathic pain support the incorporation of timing into a mechanism-based classification of neuropathic pain after SCI. The diagnosis of acute neuropathic pain after SCI is challenged by the presence of nociceptive and neuropathic pains, with the former potentially masking the latter. This may lead to an underestimation of the incidence of neuropathic pain during the very early, hyperacute time points post-injury. TRIAL REGISTRATION: ClinicalTrials.gov (Identifier: NCT01279811) PERSPECTIVE: This article presents distinct pain phenotypes of hyperacute and late presenting neuropathic pain after spinal cord injury and highlights the challenges of pain assessments in the acute phase after injury. This information may be relevant to clinical trial design and broaden our understanding of neuropathic pain mechanisms after spinal cord injury.

Routine Blood Chemistry Predicts Functional Recovery After Traumatic Spinal Cord Injury: A Post Hoc Analysis

BACKGROUND

Spinal cord injury (SCI) leads to various degrees of lifelong functional deficits. Most individuals with incomplete SCI experience a certain degree of functional recovery, especially within the first-year postinjury. However, this is difficult to predict, and surrogate biomarkers are urgently needed.

OBJECTIVE

We aimed to (1) determine if routine blood chemistry parameters are related to neurological recovery after SCI, (2) evaluate if such parameters could predict functional recovery, and (3) establish cutoff values that could inform clinical decision-making.

METHODS

We performed a post hoc analysis of routine blood chemistry parameters in patients with traumatic SCI (n = 676). Blood samples were collected between 24 and 72 hours as well as at 1, 2, 4, 8, and 52 weeks postinjury. Linear mixed models, regression analysis, and unbiased recursive partitioning (URP) of blood chemistry data were used to relate to and predict walking recovery 1 year postinjury.

RESULTS

The temporal profile of platelet counts and serum levels of albumin, alkaline phosphatase, and creatinine differentiated patients who recovered walking from those who remained wheelchair bound. The 4 blood chemistry parameters from the sample collection 8 weeks postinjury predicted functional recovery observed 1 year after incomplete SCI. Finally, URP defined a cutoff for serum albumin at 3.7 g/dL, which in combination with baseline injury severity differentiates individuals who regain ambulation from those not able to walk. Specifically, about 80% of those with albumin >3.7 g/dL recovered walking.

CONCLUSIONS

Routine blood chemistry data from the postacute phase, together with baseline injury severity, predict functional outcome after incomplete SCI.

Metabolite activity in the anterior cingulate cortex during a painful stimulus using functional MRS

To understand neurochemical brain responses to pain, proton magnetic resonance spectroscopy (1H-MRS) is used in humans in vivo to examine various metabolites. Recent MRS investigations have adopted a functional approach, where acquisitions of MRS are performed over time to track task-related changes. Previous studies suggest glutamate is of primary interest, as it may play a role during cortical processing of noxious stimuli. The objective of this study was to examine the metabolic effect (i.e., glutamate) in the anterior cingulate cortex during noxious stimulation using fMRS. The analysis addressed changes in glutamate and glutamate + glutamine (Glx) associated with the onset of pain, and the degree by which fluctuations in metabolites corresponded with continuous pain outcomes. Results suggest healthy participants undergoing tonic noxious stimulation demonstrated increased concentrations of glutamate and Glx at the onset of pain. Subsequent reports of pain were not accompanied by corresponding changes in glutamate of Glx concentrations. An exploratory analysis on sex revealed large effect size changes in glutamate at pain onset in female participants, compared with medium-sized effects in male participants. We propose a role for glutamate in the ACC related to the detection of a noxious stimulus.

Single-trial averaging improves the physiological interpretation of contact heat evoked potentials

Laser and contact heat evoked potentials (LEPs and CHEPs, respectively) provide an objective measure of pathways and processes involved in nociception. The majority of studies analyzing LEP or CHEP outcomes have done so based on conventional, across-trial averaging. With this approach, evoked potential components are potentially confounded by latency jitter and ignore relevant information contained within single trials. The current study addressed the advantage of analyzing nociceptive evoked potentials based on responses to noxious stimulations within each individual trial. Single-trial and conventional averaging were applied to data previously collected in 90 healthy subjects from 3 stimulation locations on the upper limb. The primary analysis focused on relationships between single and across-trial averaged CHEP outcomes (i.e., N2P2 amplitude and N2 and P2 latencies) and subject characteristics (i.e., age, sex, height, and rating of perceived intensity), which were examined by way of linear mixed model analysis. Single-trial averaging lead to larger N2P2 amplitudes and longer N2 and P2 latencies. Age and ratings of perceived intensity were the only subject level characteristics associated with CHEPs outcomes that significantly interacted with the method of analysis (conventional vs single-trial averaging). The strength of relationships for age and ratings of perceived intensity, measured by linear fit, were increased for single-trial compared to conventional across-trial averaged CHEP outcomes. By accounting for latency jitter, single-trial averaging improved the associations between CHEPs and physiological outcomes and should be incorporated as a standard analytical technique in future studies.

Conditioned Pain Modulation Decreases Over Time in Patients With Neuropathic Pain Following a Spinal Cord Injury

Background

Neuropathic pain is a major problem following spinal cord injury (SCI). Central mechanisms involved in the modulation of nociceptive signals have been shown to be altered at the chronic stage, and it has been hypothesized that they might play a role in the development of chronic pain.

Objective

This prospective longitudinal study aimed to describe the evolution of pain modulation mechanisms over time after SCI, and to explore the relationships with the presence of clinical (neuropathic and musculoskeletal) pain.

Methods

Patients with an SCI were assessed on admission (n = 35; average of 38 days postinjury) and discharge (n = 25; average of 131 days postinjury) using the International Spinal Cord Injury Pain Basic Data Set. Conditioned pain modulation was assessed using the cold pressor test (10 °C; 120 s) as the conditioning stimulus and tonic heat pain, applied above the level of injury, as the test stimulus (120 s). Heat pain threshold was also assessed.

Results

A marked decrease in the efficacy of conditioned pain modulation was observed over time, with 30.2% of inhibition at admission and only 12.9% at discharge on average (P = .010). This decrease was observed only in patients already suffering from neuropathic pain at admission and was not explained by a general increase in sensitivity to thermal nociceptive stimuli.

Conclusion

These results suggest that the presence of neuropathic pain leads to a decrease in conditioned pain modulation over time, rather than supporting the hypothesis that inefficient conditioned pain modulation mechanisms are leading to the development of neuropathic pain.

Association of timing of gabapentinoid use with motor recovery after spinal cord injury

OBJECTIVE

To explore the hypothesis that earlier administration of acute gabapentinoids is beneficial to motor recovery after spinal cord injury in humans.

METHODS

This is an observational study using a cohort from the European Multi-Centre Study about Spinal Cord Injury. Patient charts were reviewed to extract information regarding the administration and timing of gabapentinoid anticonvulsants. The primary outcome measure was motor scores, as measured by the International Standards for Neurological Classification of Spinal Cord Injury, collected longitudinally in the first year after injury. Sensory scores (light touch and pinprick) and functional measures (Spinal Cord Independence Measure) were secondary outcomes. Linear mixed effects regression models included a drug-by-time interaction to determine whether exposure to gabapentinoids altered recovery of muscle strength in the first year after injury.

RESULTS

A total of 201 participants were included in the study and had a median age of 46 and baseline motor score of 50. Participants were mostly men (85%) with sensory and motor complete injuries (50%). Seventy individuals (35%) were administered gabapentinoids within the first 30 days after injury, and presented with similar demographics. In the longitudinal model, the administration of gabapentinoids within 30 days after injury was associated with improved motor recovery when compared to those who did not receive gabapentinoids during this time (3.69 additional motor points from 4 to 48 weeks after injury; p = 0.03). This effect size increased as administration occurred earlier after injury (i.e., a benefit of 4.68 points when administered within 5 days).

CONCLUSIONS

This retrospective, observational study provided evidence of the beneficial effect of gabapentinoid anticonvulsants on motor recovery after spinal cord injury. More critically, it highlighted a potential time dependence, suggesting that earlier intervention is associated with better outcomes.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that gabapentinoids improve motor recovery for individuals with acute spinal cord injury.

Serum albumin as a predictor of neurological recovery after spinal cord injury: a replication study

STUDY DESIGN

This was a secondary analysis on an observational cohort study.

OBJECTIVE

To determine if serum albumin significantly associates with long-term neurological outcome (i.e., 1-year post-injury) in a contemporary cohort of individuals with spinal cord injury.

SETTING

Six rehabilitation centers across the United States.

METHODS

A secondary analysis of neurological outcomes and serum albumin concentrations was performed on data from the Spinal Cord Injury Rehabilitation study. Data was accessed from the Archive of Data on Disability to Enable Policy and research (ADDEP). The primary analysis applied unbiased recursive partitioning to examine the relationship between serum albumin, injury severity, and long-term outcomes. The analysis is accessible via https://rpubs.com/AnhKhoaVo/586028 .

RESULTS

Serum albumin concentration was significantly associated with lower extremity motor scores (LEMS) and American Spinal Injury Association Impairment Scale (AIS) grade at admission to rehabilitation. Serum albumin concentrations alone were also significantly associated with change of LEMS and marked recovery (improvement of at least 2 AIS grades and/or recovery to walking) at 1-year post injury. However, after adjusting for admission to rehabilitation LEMS and AIS grade, serum albumin was not significant.

CONCLUSION

The current study partially confirms our previous observations that serum albumin concentrations are associated with neurological outcome after spinal cord injury. As a crude prognostic biomarker, serum albumin concentration could be useful in cases where injury severity cannot be accurately assessed.

Conditioned pain modulation in elite athletes: a systematic review and meta-analysis

Background and aims Elite athletes reportedly have superior pain tolerances, but it is unclear if results extend to conditioned pain modulation (CPM). The aim of our study was to synthesize existing literature in order to determine whether CPM is increased in elite athletes compared to healthy controls. Methods A systematic review and random-effects meta-analysis was conducted. Cochrane Central Register of Controlled Trials, SPORTDiscus, PsycINFO, CINAHL, Web of Science, and PubMed were searched for English-language studies that examined CPM in adult elite athlete populations. Results Seven studies were identified; all were of poor to fair methodological quality. There was no overall difference in CPM between elite athletes and controls (Hedges g = 0.37, CI95 -0.03-0.76; p = 0.07). There was heterogeneity between studies, including one that reported significantly less CPM in elite athletes compared to controls. An exploratory meta-regression indicated that a greater number of hours trained per week was associated with higher CPM. Conclusions The overall number and quality of studies was low. Despite nominally favoring higher CPM in elite athletes, aggregate results indicate no significant difference compared to healthy controls. A possible factor explaining the high degree of variability between studies is the number of hours elite athletes spent training. Implications Based on available evidence, athletes do not have remarkable endogenous pain modulation compared to controls. High quality experimental studies are needed to address the effect of hours trained per week on CPM in athletes.

A pragmatic randomized controlled trial testing the effects of the international scientific SCI exercise guidelines on SCI chronic pain: protocol for the EPIC-SCI trial

STUDY DESIGN

Protocol for a pragmatic randomized controlled trial (the Exercise guideline Promotion and Implementation in Chronic SCI [EPIC-SCI] Trial).

PRIMARY OBJECTIVES

To test if home-/community-based exercise, prescribed according to the international SCI exercise guidelines, significantly reduces chronic bodily pain in adults with SCI.

SECONDARY OBJECTIVES

To investigate: (1) the effects of exercise on musculoskeletal and neuropathic chronic pain; (2) if reduced inflammation and increased descending inhibitory control are viable pathways by which exercise reduces pain; (3) the effects of chronic pain reductions on subjective well-being; and (4) efficiency of a home-/community-based exercise intervention.

SETTING

Exercise in home-/community-based settings; assessments in university-based laboratories in British Columbia, Canada.

METHOD

Eighty-four adults with chronic SCI, reporting chronic musculoskeletal or neuropathic pain, and not meeting the current SCI exercise guidelines, will be recruited and randomized to a 6-month Exercise or Wait-List Control condition. Exercise will occur in home/community settings and will be supported through behavioral counseling. All measures will be taken at baseline, 3-months and 6-months. Analyses will consist of linear mixed effect models, multiple regression analyses and a cost-utility analysis. The economic evaluation will examine the incremental costs and health benefits generated by the intervention compared with usual care.

ETHICS AND DISSEMINATION

The University of British Columbia Clinical Research Ethics Board approved the protocol (#H19-01650). Using an integrated knowledge translation approach, stakeholders will be engaged throughout the trial and will co-create and disseminate evidence-based recommendations and messages regarding the use of exercise to manage SCI chronic pain.

Beneficial "Pharmaceutical Pleiotropy" of Gabapentinoids in Spinal Cord Injury: A Case for Refining Standard-of-Care

Spinal cord injury results in devastating neurological deficits accompanied by lifelong disability and significant economic burden. While the development of novel compounds or cell-based interventions for spinal cord injury is unquestionably worthwhile, a complementary approach examines current standards of care and the degree to which these can be optimized to benefit long-term neurological function. Numerous classes of drugs, already in use in the acute phase of spinal cord injury, are intriguing because they (1) readily cross the blood-spinal cord barrier to modulate activity in the central nervous system and (2) are administered during a window of time in which neuroprotection, and even some repair, are feasible. Here, we review a rare case of convergent lines of evidence from both preclinical and human studies to support the early administration of a class of drug (ie, gabapentinoids) to both foster motor recovery and reduce the severity of neuropathic pain.

A Cervical Spinal Cord Hemi-Contusion Injury Model Based on Displacement Control in Non-Human Primates (Macaca fascicularis)

Non-human primate (NHP) spinal cord injury (SCI) models can be informative in the evaluation of treatments that show promise in rodent models prior to translation to humans. In the present study, we aimed to establish a cervical spinal hemi-contusion model with controlled displacement and evaluate the abnormalities in behavior, electrophysiology, histology, and magnetic resonance imaging. Twelve adult NHPs were divided into an SCI group (n = 8, 24 and 48 weeks) and a control group (n = 4). An impactor (Φ = 4 mm) was driven to compress the left C5 cord at 800 mm/sec. The contusion displacement and peak force was 4.08 ± 0.17 mm and 19.8 ± 4.6 N. The behavioral assessment showed a consistent dysfunction below the wrist and spontaneous recovery of limb function after injury. Lesion length and lesion area at the epicenter based on T2 hyperintensity were 5.68 ± 0.47 mm and 5.99 ± 0.24 mm² at 24 weeks post-injury (wpi), and 5.29 ± 0.17 mm and 5.95 ± 0.24 mm² at 48 wpi. The spared spinal cord area immuno-positive for glial fibrillary acidic protein was significantly reduced, while the staining intensity increased at 24 wpi and 48 wpi, compared with the sham group. Ipsilateral somatosensory and motor evoked potentials were dynamic, increasing in latency and decreasing in amplitude compared with pre-operative values or the contralateral values, and correlated to varying degrees with behavioral outcomes. A shift in size-frequency distribution of sensory neurons of the dorsal root ganglia (DRG) was consistent with a loss of large-diameter cells. The present study demonstrated that the NHP SCI model resulted in consistent unilateral limb dysfunction and potential plasticity in the face of loss of spinal cord and DRG tissue.

Biomarkers in Traumatic Spinal Cord Injury—Technical and Clinical Considerations: A Systematic Review

Objective. To examine (1) if serological or cerebrospinal fluid (CSF) biomarkers can be used as diagnostic and/or prognostic tools in patients with spinal cord injury (SCI) and (2) if literature provides recommendations regarding timing and source of biomarker evaluation. Data Sources. A systematic literature search to identify studies reporting on diagnostic and prognostic blood and/or CSF biomarkers in SCI was conducted in PubMed/MEDLINE, CINAHL, Science Direct, The Cochrane Library, ISI Web of Science, and PEDro. Study Selection. Clinical trials, cohort, and pilot studies on patients with traumatic SCI investigating at least one blood or CSF biomarker were included. Following systematic screening, 19 articles were included in the final analysis. PRISMA guidelines were followed to conduct this review. Data Extraction. Independent extraction of articles was completed by 2 authors using predefined inclusion criteria and study quality indicators. Data Synthesis. Nineteen studies published between 2002 and April 2019 with 1596 patients were included in the systematic review. In 14 studies, blood biomarkers were measured, 4 studies investigated CSF biomarkers, and 1 study used both blood and CSF samples. Conclusions. Serum/CSF concentrations of several biomarkers (S100b, IL-6, GFAP, NSE, tau, TNF-α, IL-8, MCP-1, pNF-H, and IP-10) following SCI are highly time dependent and related to injury severity. Future studies need to validate these markers as true biomarkers and should control for secondary complications associated with SCI. A deeper understanding of secondary pathophysiological events after SCI and their effect on biomarker dynamics may improve their clinical significance as surrogate parameters in future clinical studies.

Contact Heat Evoked Potentials Are Responsive to Peripheral Sensitization: Requisite Stimulation Parameters

The sensitizing effect of capsaicin has been previously characterized using laser and contact heat evoked potentials (LEPs and CHEPs) by stimulating in the primary area of hyperalgesia. Interestingly, only CHEPs reveal changes consistent with notion of peripheral sensitization (i.e., reduced latencies). The aim of this study was to investigate contact heat stimulation parameters necessary to detect peripheral sensitization related to the topical application of capsaicin, and therefore significantly improve the current method of measuring peripheral sensitization via CHEPs. Rapid contact heat stimulation (70°C/s) was applied from three different baseline temperatures (35, 38.5, and 42°C) to a 52°C peak temperature, before and after the topical application of capsaicin on the hand dorsum. Increased pain ratings in the primary area of hyperalgesia were accompanied by reduced N2 latency. Changes in N2 latency were, however, only significant following stimulation from 35 and 38.5°C baseline temperatures. These findings suggest that earlier recruitment of capsaicin-sensitized afferents occurs between 35 and 42°C, as stimulations from 42°C baseline were unchanged by capsaicin. This is in line with reduced thresholds of type II A-delta mechanoheat (AMH) nociceptors following sensitization. Conventional CHEP stimulation, with a baseline temperature below 42°C, is well suited to objectively detect evidence of peripheral sensitization.

Using ecological momentary assessment to evaluate neuropathic pain experienced by adults with SCI: recommendations and participant perceptions

PURPOSE

Neuropathic pain is a debilitating consequence of spinal cord injury. Ecological momentary assessment can be a valuable research tool for understanding temporal fluctuations in neuropathic pain and designing effective management strategies. The objectives of this study were to (a) describe strategies necessary to adapt ecological momentary assessment to measure neuropathic pain in adults with spinal cord injury, and (b) explore participant perceptions of using ecological momentary assessment to measure pain sensations.

METHODS

End-users with spinal cord injury provided input to guide development of an ecological momentary assessment protocol. Six adults with spinal cord injury (ages 27-50 years, M = 39.33 ± 8.24) engaged in the six-day protocol and completed six daily neuropathic pain assessments. Upon finishing participants completed a semi-structured interview regarding their protocol experiences. A qualitative content analysis was used to analyze the interview data.

RESULTS

Participants reported that this specific ecological momentary assessment protocol was unobtrusive to their daily routines, and effectively captured their neuropathic pain sensations. However, participants experienced increased neuropathic pain due to the repeated nature of assessments.

CONCLUSION

Ecological momentary assessment can capture the dynamic nature of neuropathic pain experienced by persons with spinal cord injury. However, caution should be taken when designing intensive pain-related protocols to minimize pain exacerbation.IMPLICATIONS FOR REHABILITATIONNeuropathic pain affects up to 75% of people with spinal cord injury and is one of the most frequently occurring, debilitating forms of pain.Appropriate and feasible pain data collection methods are necessary to acquire a better understanding of how neuropathic pain manifests in people with spinal cord injury.Implementing ecological momentary assessment in a rehabilitation setting may help facilitate the monitoring of neuropathic pain for both rehabilitation professionals and persons with SCI.Using ecological momentary assessment may lead to a better understanding of individual temporal patterns of neuropathic pain that could inform the design of tailored neuropathic pain management techniques.

Myelin Water Fraction and Intra/Extracellular Water Geometric Mean T2 Normative Atlases for the Cervical Spinal Cord from 3T MRI

BACKGROUND AND PURPOSE

Acquiring and interpreting quantitative myelin-specific MRI data at an individual level is challenging because of technical difficulties and natural myelin variation in the population. To overcome these challenges, we used multiecho T₂ myelin water imaging (MWI) to create T₂ metric healthy population atlases that depict the mean and variation of myelin water fraction (MWF), and intra- and extracellular water mobility as described by geometric mean T₂ (IEGMT₂ ).

METHODS

Cervical cord MWI was performed at 3T on 20 healthy individuals (10M/10F, mean age: 36 years) and 3 relapsing remitting multiple sclerosis (RRMS) participants (1M/2F, age: 39/42/37 years). Anatomical data were collected for the purpose of image segmentation and registration. Atlases were created by coregistering and averaging T₂ metrics from all controls. Voxel-wise z-score maps from 3 RRMS participants were produced to demonstrate the preliminary utility of the MWF and IEGMT₂ atlases.

RESULTS

The average MWF atlas provides a representation of myelin in the spinal cord consistent with well-known spinal cord anatomical characteristics. The IEGMT₂ atlas also depicted structural variations in the spinal cord. Z-score analysis illustrated distinct abnormalities in MWF and IEGMT₂ in the 3 RRMS cases.

CONCLUSIONS

Our findings highlight the potential for using a quantitative T₂ relaxation metric atlas to visualize and detect pathology in spinal cord. Our MWF and IEGMT₂ atlases (URL: https://sourceforge.net/projects/mwi-spinal-cord-atlases/) can serve as normative references in the cervical spinal cord for other studies.

Myelin Water Atlas: A Template for Myelin Distribution in the Brain

BACKGROUND AND PURPOSE

Myelin water imaging (MWI) is a magnetic resonance imaging technique that quantifies myelin in-vivo. Although MWI has been extensively applied to study myelin-related diseases in groups, clinical use in individual patients is challenging mainly due to population heterogeneity. The purpose of this study was twofold: (1) create a normative brain myelin water atlas depicting the population mean and regional variability of myelin content; and (2) apply the myelin atlas to assess the degree of demyelination in individuals with multiple sclerosis (MS).

METHODS

3T MWI was performed on 50 healthy adults (25 M/25 F, mean age 25 years [range 17-42 years]). The myelin water atlas was created by averaging coregistered myelin water fraction (MWF) maps from all healthy individuals. To illustrate the preliminary utility of the atlas, white matter (WM) regional MWF variations were evaluated and voxel-wise z-score maps (z < -1.96) from the MWI of three MS participants were produced to assess individually the degree of demyelination.

RESULTS

The myelin water atlas demonstrated significant MWF variation across control WM. No significant MWF differences were found between male and female healthy participants. MS z-score maps revealed diffuse regions of demyelination in the two participants with Expanded Disability Status Scale (EDSS) = 2.0 but not in the participant with EDSS = 0.

CONCLUSIONS

The myelin water atlas can be used as a reference (URL: https://sourceforge.net/projects/myelin-water-atlas/) to demonstrate areas of demyelination in individual MS participants. Future studies will expand the atlas age range, account for education, and other variables that may affect myelination.

A Longitudinal Study of the Neurologic Safety of Acute Baclofen Use After Spinal Cord Injury

The objective of our study was to determine whether treatment with baclofen is neurologically safe with respect to exposure during recovery from spinal cord injury. We performed a secondary longitudinal analysis of a cohort of adult patients with traumatic acute spinal cord injury. Cumulative baclofen dose was computed over the first 4 weeks following injury from concomitant medication information from a completed clinical trial. The main outcome measure was neurologic status, which was assessed over 52 weeks with "marked recovery" defined as the conversion to higher sensory and motor function. To complete the drug safety profile, drug toxicity was assessed with assays from standard blood work. Multivariable Cox regression was used to compute hazard ratios (HRs) and 95% confidence intervals (CIs). Of the cohort (n = 651), 18% (n = 115) received baclofen within 4 weeks post injury. Baclofen use was associated with higher rates of marked neurologic recovery, even after adjustment for injury severity (HR = 2.1, 95% CI 1.5-3.0 for high dose vs none). Baclofen exposure was not associated with liver or renal side effects. The use of other medications indicated for spasticity was not associated with neurological outcomes. Overall, this longitudinal analysis provides level 3 evidence on the neurologic safety of baclofen and potential beneficial effects on recovery in the early days after acute traumatic spinal cord injury. The usefulness of concomitant medication files from completed clinical trials is highlighted. We also highlight the importance of incorporating logical patient questions and neurological outcomes into research addressing drug safety.

Rapid myelin water imaging for the assessment of cervical spinal cord myelin damage

Background

Rapid myelin water imaging (MWI) using a combined gradient and spin echo (GRASE) sequence can produce myelin specific metrics for the human brain. Spinal cord MWI could be similarly useful, but technical challenges have hindered routine application. GRASE rapid MWI was recently successfully implemented for imaging of healthy cervical spinal cord and may complement other advanced imaging methods, such as diffusion tensor imaging (DTI) and quantitative T₁ (qT₁).

Objective

To demonstrate the feasibility of cervical cord GRASE rapid MWI in multiple sclerosis (MS), primary lateral sclerosis (PLS) and neuromyelitis optica spectrum disorder (NMO), with comparison to DTI and qT₁ metrics.

Methods

GRASE MWI, DTI and qT₁ data were acquired in 2 PLS, 1 relapsing-remitting MS (RRMS), 1 primary-progressive MS (PPMS) and 2 NMO subjects, as well as 6 age (±3 yrs) and sex matched healthy controls (HC). Internal cord structure guided template registrations, used for region of interest (ROI) analysis. Z score maps were calculated for the difference between disease subject and mean HC metric values.

Results

PLS subjects had low myelin water fraction (MWF) in the lateral funiculi compared to HC. RRMS subject MWF was heterogeneous within the cord. The PPMS subject showed no trends in ROI results but had a region of low MWF Z score corresponding to a focal lesion. The NMO subject with a longitudinally extensive transverse myelitis lesion had low values for whole cord mean MWF of 12.8% compared to 24.3% (standard deviation 2.2%) for HC. The NMO subject without lesions also had low MWF compared to HC. DTI and qT₁ metrics showed similar trends, corroborating the MWF results and providing complementary information.

Conclusion

GRASE is sufficiently sensitive to detect decreased myelin within MS spinal cord plaques, NMO lesions, and PLS diffuse spinal cord injury. Decreased MWF in PLS is consistent with demyelination secondary to motor neuron degeneration. GRASE MWI is a feasible method for rapid assessment of myelin content in the cervical spinal cord and provides complementary information to that of DTI and qT₁ measures.

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Downstream myelin changes in motor tracts of primary lateral sclerosis spinal cord.

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Low myelin water fraction in multiple sclerosis and neuromyelitis optica cord lesions.

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Diffuse demyelination evidence in neuromyelitis optica normal-appearing white matter.

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Myelin water imaging provides complementary information to diffusion and T₁ metrics.

New life for an old idea: Assessing tonic heat pain by means of participant controlled temperature

BACKGROUND

Temporal changes of pain perception to prolonged tonic heat pain are conventionally assessed using a computerized visual analog scale. Such a rating-based approach is, however, prone to floor and ceiling effects, which limit the assessment of temporal changes in perception. Thus, alternative methods that overcome these shortcomings are warranted.

NEW METHOD

The aim of this study was to assess the feasibility and reliability of a psychophysical approach, i.e., participant-controlled temperature (PCT), to evaluate ongoing human perception of tonic heat pain. Fifty participants were presented with a 45 °C stimulus on the non-dominant hand, and were instructed to maintain their initial sensation for two minutes via a feedback controller in the dominant hand. A subset of participants (n = 17) performed PCT tonic heat protocols on two different days to determine the test-retest reliability. As participants controlled temperature to maintain a stable pain perception, any adjustments made reflected shifts in their perception of heat.

RESULTS

In 33 (71.7%) participants, we observed an initial adaptation (participant increased temperature) followed by temporal summation of pain (participant decreased temperature). Twelve participants (26.1%) showed only adaptation and one (2.2%) only temporal summation. No sex differences were observed, nor did the initial rating of pain have an effect on PCT outcomes. Temporal summation of pain showed moderate to substantial reliability upon retest.

CONCLUSIONS

PCT represents can be reliably performed using a contact heat stimulator to measure the temporal summation of pain. The standardized setup and overall good reliability of the outcome measures facilitate a sound implementation into the clinical work-up of patients with pain conditions.

Ecological fallacy as a novel risk factor for poor translation in neuroscience research: A systematic review and simulation study

BACKGROUND

Translational neuroscience is largely concerned with establishing causal links between biological processes and functional outcomes. Exciting new methods have emerged and top-tier biomedical journals are placing increasingly high demand for experiments that link outcomes. One pitfall to making these connections is the "ecological fallacy"-establishing a relationship between outcomes based on aggregate (averaged) results (a distinct issue from correlation vs causation).

METHODS

To showcase the ecological fallacy, we first used simulated data to define and demonstrate the problem. Next, we performed a systematic review to determine the prevalence of the fallacy in top-tier biomedical journals (Science, Nature Medicine, Neuron, Nature, Nature Neuroscience, Cell). Based on our own research interests and specializations, we specifically focused on recent publications in the area of spinal cord injury and regenerative medicine.

RESULTS

Of the articles reviewed which examined a relationship between central nervous system regeneration and a behavioural outcome, 100% (21/21) were subject to possible ecological fallacy.

CONCLUSIONS

Ecological fallacy is highly prevalent in neuroscience research and could partially account for translation failures in this field. Reporting guidelines for in vivo experiments should include subject-level correlation analyses for the primary outcomes.

Not Hot, but Sharp: Dissociation of Pinprick and Heat Perception in Snake Eye Appearance Myelopathy

Following a traumatic spinal cord injury, a 53-year-old male developed a central cord syndrome with at-level neuropathic pain. Magnetic resonance imaging revealed a classical “snake eye” appearance myelopathy, with marked hyperintensities at C5-C7. Clinical examination revealed intact pinprick sensation coupled with lost or diminished thermal/heat sensation. This dissociation could be objectively confirmed through multi-modal neurophysiological assessments. Specifically, contact heat evoked potentials were lost at-level, while pinprick evoked potentials were preserved. This pattern corresponds with that seen after surgical commissural myelotomy. To our knowledge, this is the first time such a dissociation has been objectively documented, highlighting the diagnostic potential of multi-modal neurophysiological assessments. In future studies, a comprehensive assessment of different nociceptive modalities may help elucidate the pathophysiology of neuropathic pain.

Progression of Neuropathic Pain after Acute Spinal Cord Injury: A Meta-Analysis and Framework for Clinical Trials

The translation of therapeutic interventions to humans with spinal cord injury with the goal of promoting growth and repair in the central nervous system could, inadvertently, drive mechanisms associated with the development of neuropathic pain. A framework is needed to evaluate the probability that a therapeutic intervention for acute spinal cord injury modifies the progression of neuropathic pain. We analyzed a large, longitudinal dataset from the European Multi-Center Study about Spinal Cord Injury (EMSCI) and compared these observations with a previously published Swedish/Danish cohort. A meta-analysis was performed to produce aggregate estimates for the transition period between 1-6 months and the transition period between 1-12 months after injury. A secondary analysis used logistic regression to explore associations between the progression of neuropathic pain and demographics, pain characteristics, and injury characteristics. For overall neuropathic pain, 72% presenting with pain symptoms at one month reported persisting symptoms at six months, and 23% who did not have neuropathic pain at one month later had it develop. From 1-12 months, there was a similar likelihood of pain persisting (69%) and slightly higher rate of pain developing (36%). Characteristics that were significantly associated with the progression of pain included age and sensory and motor preservation. We provide historical benchmarks for estimating the progression of neuropathic pain during the first year after acute SCI. This information will be useful for comparison and evaluating safety during early phase acute spinal cord injury trials.

Sensorimotor plasticity after spinal cord injury: a longitudinal and translational study

Objective

The objective was to track and compare the progression of neuroplastic changes in a large animal model and humans with spinal cord injury.

Methods

A total of 37 individuals with acute traumatic spinal cord injury were followed over time (1, 3, 6, and 12 months post-injury) with repeated neurophysiological assessments. Somatosensory and motor evoked potentials were recorded in the upper extremities above the level of injury. In a reverse-translational approach, similar neurophysiological techniques were examined in a porcine model of thoracic spinal cord injury. Twelve Yucatan mini-pigs underwent a contusive spinal cord injury at T10 and tracked with somatosensory and motor evoked potentials assessments in the fore- and hind limbs pre- (baseline, post-laminectomy) and post-injury (10 min, 3 h, 12 weeks).

Results

In both humans and pigs, the sensory responses in the cranial coordinates of upper extremities/forelimbs progressively increased from immediately post-injury to later time points. Motor responses in the forelimbs increased immediately after experimental injury in pigs, remaining elevated at 12 weeks. In humans, motor evoked potentials were significantly higher at 1-month (and remained so at 1 year) compared to normative values.

Conclusions

Despite notable differences between experimental models and the human condition, the brain's response to spinal cord injury is remarkably similar between humans and pigs. Our findings further underscore the utility of this large animal model in translational spinal cord injury research.

Contact heat evoked potentials: Reliable acquisition from lower extremities

OBJECTIVE

To investigate test-retest reliability of contact heat evoked potentials (CHEPs) from lower extremities using two different stimulation protocols, i.e., normal and increased baseline temperature.

METHODS

A total of 32 able-bodied subjects were included and a subset (N = 22) was retested. CHEPs were recorded from three different dermatomes of the lower extremity (i.e., L2, L5, and S2). Test-retest reliability of CHEPs acquisition after simulation in various lower limb dermatomes using different stimulation protocols was analyzed.

RESULTS

The study revealed an improved acquisition of CHEPS employing the increased baseline protocol, particularly when stimulating more distal sites, i.e., dermatome L5 and S2. Based on repeatability coefficients, CHEP latency (N2 potential) emerged as the most robust CHEP parameter. Although CHEP amplitudes (N2P2 complex) and pain ratings were decreased in the retest, amplitudes still showed fair to excellent intraclass correlation coefficients using normal baseline or increased baseline temperature, respectively.

CONCLUSIONS

This is the first study to demonstrate that CHEPs acquisition from the lower extremities is improved by increasing the baseline temperature of the thermode.

SIGNIFICANCE

This study highlights the usability of CHEPs as a viable diagnostic method to study small fiber integrity.

Serum Albumin Predicts Long-Term Neurological Outcomes After Acute Spinal Cord Injury

Background. There is a need to identify reliable biomarkers of spinal cord injury recovery for clinical practice and clinical trials. Objective. Our objective was to correlate serum albumin levels with spinal cord injury neurological outcomes. Methods. We performed a secondary analysis of patients with traumatic spinal cord injury (n = 591) participating in the Sygen clinical trial. Serum albumin concentrations were obtained as part of routine blood chemistry analysis, at trial entry (24-72 hours), 1, 2, and 4 weeks after injury. The primary outcomes were “marked recovery” and lower extremity motor scores, derived from the International Standards for the Neurological Classification of Spinal Cord Injury. Data were analyzed with multivariable logistic and linear regression to adjust for potential confounders. Results. Serum albumin was significantly associated with spinal cord injury neurological outcomes. Higher serum albumin concentrations at 1, 2, and 4 weeks were associated with higher 52-week lower extremity motor score. Similarly, the odds of achieving “marked neurological recovery” was greater for individuals with higher serum albumin concentrations. The association between serum albumin concentrations and neurological outcomes was independent of initial injury severity, treatment with GM-1, and polytrauma. Conclusions. In spinal cord injury, serum albumin is an independent marker of long-term neurological outcomes. Serum albumin could serve as a feasible biomarker for prognosis at the time of injury and stratification in clinical trials.

Assessing structure and function of myelin in cervical spondylotic myelopathy: Evidence of demyelination

PURPOSE

To assess the extent of demyelination in cervical spondylotic myelopathy (CSM) using myelin water imaging (MWI) and electrophysiologic techniques.

METHODS

Somatosensory evoked potentials (SSEPs) and MWI were acquired in 14 patients with CSM and 18 age-matched healthy controls. MWI was performed on a 3.0T whole body magnetic resonance scanner. Myelin water fraction (MWF) was extracted for the dorsal columns and whole cord. SSEPs and MWF were also compared with conventional MRI outcomes, including T2 signal intensity, compression ratio, maximum spinal cord compression (MSCC), and maximum canal compromise (MCC).

RESULTS

Group analysis showed marked differences in T2 signal intensity, compression ratio, MSCC, and MCC between healthy controls and patients with CSM. There were no group differences in MWF and SSEP latencies. However, patients with CSM with pathologic SSEPs exhibited reduction in MWF (p < 0.05). MWF was also correlated with SSEP latencies.

CONCLUSION

Our findings provide evidence of decreased myelin content in the spinal cord associated with impaired spinal cord conduction in patients with CSM. While conventional MRI are of great value to define the extent of cord compression, they show a limited correlation with functional deficits (i.e., delayed SSEPs). MWI provides independent and complementary readouts to spinal cord compression, with a high specificity to detect impaired conduction.

Open Access Platforms in Spinal Cord Injury: Existing Clinical Trial Data to Predict and Improve Outcomes

Recovery from acute spinal cord injury (SCI) is characterized by extensive heterogeneity, resulting in uncertain prognosis. Reliable prediction of recovery in the acute phase benefits patients and their families directly, as well as improves the likelihood of detecting efficacy in clinical trials. This issue of heterogeneity is not unique to SCI. In fields such as traumatic brain injury, Parkinson's disease, and amyotrophic lateral sclerosis, one approach to understand variability in recovery has been to make clinical trial data widely available to the greater research community. We contend that the SCI community should adopt a similar approach in providing open access clinical trial data.

Thermal grill conditioning: Effect on contact heat evoked potentials

The ‘thermal grill illusion’ (TGI) is a unique cutaneous sensation of unpleasantness, induced through the application of interlacing warm and cool stimuli. While previous studies have investigated optimal parameters and subject characteristics to evoke the illusion, our aim was to examine the modulating effect as a conditioning stimulus. A total of 28 healthy control individuals underwent three testing sessions on separate days. Briefly, 15 contact heat stimuli were delivered to the right hand dorsum, while the left palmar side of the hand was being conditioned with either neutral (32 °C), cool (20 °C), warm (40 °C), or TGI (20/40 °C). Rating of perception (numeric rating scale: 0–10) and evoked potentials (i.e., N1 and N2P2 potentials) to noxious contact heat stimuli were assessed. While cool and warm conditioning decreased cortical responses to noxious heat, TGI conditioning increased evoked potential amplitude (N1 and N2P2). In line with other modalities of unpleasant conditioning (e.g., sound, visual, and olfactory stimulation), cortical and possibly sub-cortical modulation may underlie the facilitation of contact heat evoked potentials.

Normative data for the segmental acquisition of contact heat evoked potentials in cervical dermatomes

Contact heat evoked potentials (CHEPs) represent a neurophysiological approach to assess conduction in the spinothalamic tract. The aim of this study was to establish normative values of CHEPs acquired from cervical dermatomes (C4, C6, C8) and examine the potential confounds of age, sex, and height. 101 (49 male) healthy subjects of three different age groups (18–40, 41–60, and 61–80 years) were recruited. Normal (NB, 35–52 °C) followed by increased (IB, 42–52 °C) baseline stimulation protocols were employed to record CHEPs. Multi-variate linear models were used to investigate the effect of age, sex, and height on the CHEPs parameters (i.e., N2 latency, N2P2 amplitude, rating of perceived intensity). Compared to NB, IB stimulation reduced latency jitter within subjects, yielding larger N2P2 amplitudes, and decreased inter-subject N2 latency variability. Age was associated with reduced N2P2 amplitude and prolonged N2 latency. After controlling for height, male subjects had significantly longer N2 latencies than females during IB stimulation. The study provides normative CHEPs data in a large cohort of healthy subjects from segmentally examined cervical dermatomes. Age and sex were identified as important factors contributing to N2 latency and N2P2 amplitude. The normative data will improve the diagnosis of spinal cord pathologies.

Neuropathic pain following traumatic spinal cord injury: Models, measurement, and mechanisms

Neuropathic pain following spinal cord injury (SCI) is notoriously difficult to treat and is a high priority for many in the SCI population. Resolving this issue requires animal models fidelic to the clinical situation in terms of injury mechanism and pain phenotype. This Review discusses the means by which neuropathic pain has been induced and measured in experimental SCI and compares these with human outcomes, showing that there is a substantial disconnection between experimental investigations and clinical findings in a number of features. Clinical injury level is predominantly cervical, whereas injury in the laboratory is modeled mainly at the thoracic cord. Neuropathic pain is primarily spontaneous or tonic in people with SCI (with a relatively smaller incidence of allodynia), but measures of evoked responses (to thermal and mechanical stimuli) are almost exclusively used in animals. There is even the question of whether pain per se has been under investigation in most experimental SCI studies rather than simply enhanced reflex activity with no affective component. This Review also summarizes some of the problems related to clinical assessment of neuropathic pain and how advanced imaging techniques may circumvent a lack of patient/clinician objectivity and discusses possible etiologies of neuropathic pain following SCI based on evidence from both clinical studies and animal models, with examples of cellular and molecular changes drawn from the entire neuraxis from primary afferent terminals to cortical sensory and affective centers. © 2016 Wiley Periodicals, Inc.

Association of pain and CNS structural changes after spinal cord injury

Traumatic spinal cord injury (SCI) has been shown to trigger structural atrophic changes within the spinal cord and brain. However, the relationship between structural changes and magnitude of neuropathic pain (NP) remains incompletely understood. Voxel-wise analysis of anatomical magnetic resonance imaging data provided information on cross-sectional cervical cord area and volumetric brain changes in 30 individuals with chronic traumatic SCI and 31 healthy controls. Participants were clinically assessed including neurological examination and pain questionnaire. Compared to controls, individuals with SCI exhibited decreased cord area, reduced grey matter (GM) volumes in anterior cingulate cortex (ACC), left insula, left secondary somatosensory cortex, bilateral thalamus, and decreased white matter volumes in pyramids and left internal capsule. The presence of NP was related with smaller cord area, increased GM in left ACC and right M1, and decreased GM in right primary somatosensory cortex and thalamus. Greater GM volume in M1 was associated with amount of NP. Below-level NP-associated structural changes in the spinal cord and brain can be discerned from trauma-induced consequences of SCI. The directionality of these relationships reveals specific changes across the neuroaxis (i.e., atrophic changes versus increases in volume) and may provide substrates of underlying neural mechanisms in the development of NP.