Predicting the Risk for Central Pain Using the Sensory Components of the International Standards for Neurological Classification of Spinal Cord Injury

Analysis of the influencing factors related to neuropathic pain in patients with spinal cord injuries: a retrospective study

BACKGROUND

The aim of this study was to investigate the related influencing factors of neuropathic pain (NP) in patients with spinal cord injury (SCI).

METHODS

Patients diagnosed with SCI between January 2016 and December 2019 in the Department of Rehabilitation Medicine, Affiliated Hospital of Guizhou Medical University, were screened for NP by using the Douleur Neuropathique 4 (DN4) questionnaire. A total of 133 patients diagnosed with SCI with NP were finally included in the study. We collected the patients' basic information, including gender, age, body mass index (BMI), disease course, injury segment, American Spinal Injury Association (ASIA) grade, occupation, educational level, whether painkillers were used, stability of economic support, and pain level. Univariate and multiple ordered logistic regression analyses were used to examine the influencing factors of NP in the patients with SCI.

RESULTS

The chi-square test revealed that disease course, injury level, severity of SCI (ASIA classification), stable economic support during hospitalization, and the use of painkillers had statistical significance (p < .01). A multivariate logistic regression analysis was performed to analyze the influencing factors of NP. ASIA grade, stable economic support, and use of painkillers were independent influencing factors of NP in patients with SCI, among which injury severity was the independent risk factor (odds ratio [OR] > 1). Stable economic support and painkiller use were protective factors (OR < 1).

CONCLUSIONS

In this study, we found no significant correlation between NP after SCI and sex, age, BMI, disease course, injury level, and occupation. However, the injury severity was an independent risk factor, and stable economic support and painkiller use were protective factors.

Noxious radiant heat evokes bi-component nociceptive withdrawal reflexes in spinal cord injured humans-A clinical tool to study neuroplastic changes of spinal neural circuits

Investigating nocifensive withdrawal reflexes as potential surrogate marker for the spinal excitation level may widen the understanding of maladaptive nociceptive processing after spinal cord injury (SCI). The aim of this prospective, explorative cross-sectional observational study was to investigate the response behavior of individuals with SCI to noxious radiant heat (laser) stimuli and to assess its relation to spasticity and neuropathic pain, two clinical consequences of spinal hyperexcitability/spinal disinhibition. Laser stimuli were applied at the sole and dorsum of the foot and below the fibula head. Corresponding reflexes were electromyography (EMG) recorded ipsilateral. Motor responses to laser stimuli were analyzed and related to clinical readouts (severity of injury/spasticity/pain), using established clinical assessment tools. Twenty-seven participants, 15 with SCI (age 18-63; 6.5 years post-injury; AIS-A through D) and 12 non-disabled controls, [non-disabled controls (NDC); age 19-63] were included. The percentage of individuals with SCI responding to stimuli (70-77%; p < 0.001), their response rates (16-21%; p < 0.05) and their reflex magnitude (p < 0.05) were significantly higher compared to NDC. SCI-related reflexes clustered in two time-windows, indicating involvement of both A-delta- and C-fibers. Spasticity was associated with facilitated reflexes in SCI (Kendall-tau-b p ≤ 0.05) and inversely associated with the occurrence/severity of neuropathic pain (Fisher's exact p < 0.05; Eta-coefficient p < 0.05). However, neuropathic pain was not related to reflex behavior. Altogether, we found a bi-component motor hyperresponsiveness of SCI to noxious heat, which correlated with spasticity, but not neuropathic pain. Laser-evoked withdrawal reflexes may become a suitable outcome parameter to explore maladaptive spinal circuitries in SCI and to assess the effect of targeted treatment strategies. Registration: https://drks.de/search/de/trial/DRKS00006779.

Revisiting the Examination of Sharp/Dull Discrimination as Clinical Measure of Spinothalamic Tract Integrity

Objective: Revisiting the sharp/dull discrimination as clinical measure of spinothalamic tract function considering the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI). Three clinically relevant factors were evaluated as to their impact on reliability: (1) the localization of dermatomes in relation to the sensory level, (2) the examination tool, and (3) the threshold of correct answers for grading of a preserved sharp/dull discrimination.

Design: Prospective monocentric psychometric study.

Setting: Spinal Cord Injury Center, Heidelberg University Hospital, Germany.

Participants: Convenient sample of 21 individuals with subacute spinal cord injury (age: 31–82 years) and 20 individuals without spinal cord injury (age: 24–63 years).

Assessment: All participants underwent three assessments for sharp/dull discrimination, applying five commonly used examination tools in seven dermatomes, performed by three trained examiners under conditions in accordance with ISNCSCI.

Main Outcome Measures: Assessment of interrater reliability by determining both the Fleiss kappa (κ) coefficient and the percentage agreement between raters. Data were dichotomized regarding the ISNCSCI threshold.

Results: Interrater reliability in individuals with SCI was overall substantial (κ = 0.68; CI 0.679–0.681) and moderate (κ = 0.54; CI 0.539–0.543) in dermatomes below the sensory level. All applied tools led to at least moderate reliability below the sensory level (lowest κ = 0.44; CI 0.432–0.440), with the officially endorsed safety pin achieving the highest (substantial) reliability (κ = 0.64; CI 0.638–0.646). Percentage agreement differed between non-SCI (97.3%) and formally intact above level dermatomes in SCI (89.2%).

Conclusions: Sharp/dull discrimination as a common clinical examination technique for spinothalamic tract function is a reliable assessment. Independent from the used examination tools, reliability was substantial, with the medium-sized safety pin delivering the most favorable results. Notwithstanding this, all other tools could be considered if a safety pin is not available. Regarding interrater reliability and guessing probability, a threshold of 80% correct responses for preserved sharp/dull discrimination appears to be most suitable, which is in line with current clinical approaches and ISNCSCI. The causal attribution of the identified differences in sharp/dull discrimination between clinically intact dermatomes of individuals with SCI and unaffected dermatomes of individuals without SCI requires future work.

Clinical Trial Registration Number (German Clinical Trials Register): DRKS00015334 (https://www.drks.de).

Biomarkers for predicting central neuropathic pain occurrence and severity after spinal cord injury: results of a long-term longitudinal study

Central neuropathic pain (CNP) after spinal cord injury (SCI) is debilitating and immensely impacts the individual. Central neuropathic pain is relatively resistant to treatment administered after it develops, perhaps owing to irreversible pathological processes. Although preemptive treatment may overcome this shortcoming, its administration necessitates screening patients with clinically relevant biomarkers that could predict CNP early post-SCI. The aim was to search for such biomarkers by measuring pronociceptive and for the first time, antinociceptive indices early post-SCI. Participants were 47 patients with acute SCI and 20 healthy controls. Pain adaptation, conditioned pain modulation (CPM), pain temporal summation, wind-up pain, and allodynia were measured above, at, and below the injury level, at 1.5 months after SCI. Healthy control were tested at corresponding regions. Spinal cord injury patients were monitored for CNP emergence and characteristics at 3 to 4, 6 to 7, and 24 months post-SCI. Central neuropathic pain prevalence was 57.4%. Central neuropathic pain severity, quality, and aggravating factors but not location somewhat changed over 24 months. Spinal cord injury patients who eventually developed CNP exhibited early, reduced at-level pain adaptation and CPM magnitudes than those who did not. The best predictor for CNP emergence at 3 to 4 and 7 to 8 months was at-level pain adaptation with odds ratios of 3.17 and 2.83, respectively (∼77% probability) and a cutoff value with 90% sensitivity. Allodynia and at-level CPM predicted CNP severity at 3 to 4 and 24 months, respectively. Reduced pain inhibition capacity precedes, and may lead to CNP. At-level pain adaptation is an early CNP biomarker with which individuals at risk can be identified to initiate preemptive treatment.

Interrelationship of Neurogenic Obesity and Chronic Neuropathic Pain in Persons With Spinal Cord Injury

The prevalence of obesity and of neuropathic pain are both estimated at above 50% in the population of people with chronic spinal cord injury (SCI). These secondary consequences of SCI have significant negative impact on physical functioning, activities of daily living, and quality of life. Investigations of relationships between weight or body composition and chronic neuropathic pain in people with SCI are lacking, but investigations in non-SCI cohorts suggest an association between obesity and the presence and severity of neuropathic pain conditions. In the present article, we present a review of the literature linking obesity and neuropathic pain and summarize findings suggesting that metabolic syndrome and chronic, systemic inflammation due to excess adiposity increase the risk for neuropathic pain after an SCI.

Neuropathic Pain: From Mechanisms to Treatment

Neuropathic pain caused by a lesion or disease of the somatosensory nervous system is a common chronic pain condition with major impact on quality of life. Examples include trigeminal neuralgia, painful polyneuropathy, postherpetic neuralgia, and central poststroke pain. Most patients complain of an ongoing or intermittent spontaneous pain of, for example, burning, pricking, squeezing quality, which may be accompanied by evoked pain, particular to light touch and cold. Ectopic activity in, for example, nerve-end neuroma, compressed nerves or nerve roots, dorsal root ganglia, and the thalamus may in different conditions underlie the spontaneous pain. Evoked pain may spread to neighboring areas, and the underlying pathophysiology involves peripheral and central sensitization. Maladaptive structural changes and a number of cell-cell interactions and molecular signaling underlie the sensitization of nociceptive pathways. These include alteration in ion channels, activation of immune cells, glial-derived mediators, and epigenetic regulation. The major classes of therapeutics include drugs acting on α₂δ subunits of calcium channels, sodium channels, and descending modulatory inhibitory pathways.

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.

Neuropathic Pain After Spinal Cord Injury: Challenges and Research Perspectives

Neuropathic pain is a debilitating consequence of spinal cord injury (SCI) that remains difficult to treat because underlying mechanisms are not yet fully understood. In part, this is due to limitations of evaluating neuropathic pain in animal models in general, and SCI rodents in particular. Though pain in patients is primarily spontaneous, with relatively few patients experiencing evoked pains, animal models of SCI pain have primarily relied upon evoked withdrawals. Greater use of operant tasks for evaluation of the affective dimension of pain in rodents is needed, but these tests have their own limitations such that additional studies of the relationship between evoked withdrawals and operant outcomes are recommended. In preclinical SCI models, enhanced reflex withdrawal or pain responses can arise from pathological changes that occur at any point along the sensory neuraxis. Use of quantitative sensory testing for identification of optimal treatment approach may yield improved identification of treatment options and clinical trial design. Additionally, a better understanding of the differences between mechanisms contributing to at- versus below-level neuropathic pain and neuropathic pain versus spasticity may shed insights into novel treatment options. Finally, the role of patient characteristics such as age and sex in pathogenesis of neuropathic SCI pain remains to be addressed.

Increased psychological distress among individuals with spinal cord injury is associated with central neuropathic pain rather than the injury characteristics

STUDY DESIGN

Cross-sectional study.

OBJECTIVES

Central neuropathic pain (CNP) is common after spinal cord injury (SCI). The psychological impact of CNP is not clear. Previous studies reported depression and pain catastrophizing among patients with SCI and CNP; however, the lack of control groups prevented discerning whether these were attributed to CNP or to the SCI itself. The aim was to examine the psychological distress among individuals with SCI with and without CNP and controls to evaluate its impact and possible source.

SETTING

Outpatient clinic of a large rehabilitation center.

METHODS

Individuals with SCI and CNP (n = 27) and without CNP (n = 23), and able-bodied controls (n = 20) participated. Data collection included sociodemographics, SCI characteristics, and level of post-traumatic stress disorder (PTSD), anxiety, stress, depression, and pain catastrophizing. The sensory, affective, and cognitive dimensions of CNP were analyzed.

RESULTS

Individuals with SCI and CNP exhibited elevated levels of PTSD, anxiety, stress, depression, and pain catastrophizing compared to the two control groups, which presented similar levels. The psychological variables among the CNP group correlated positively only with the affective dimension of CNP. Neither CNP nor the psychological variables correlated with SCI characteristics.

CONCLUSIONS

Irrespective of CNP intensity, the affective dimension (suffering) is associated with increased psychological distress. Perhaps individual differences in the response to SCI and/or individual traits rather than the mere exposure to SCI may have a role in the emergence of CNP and psychological distress/mood dysfunction. Rehabilitation programs should prioritize stress management and prevention among individuals with SCI and CNP.

Neuropathic pain and spasticity: intricate consequences of spinal cord injury

STUDY DESIGN

The 2016 International Spinal Cord Society Sir Ludwig Guttmann Lecture.

OBJECTIVES

The aim of this review is to identify different symptoms and signs of neuropathic pain and spasticity after spinal cord injury (SCI) and to present different methods of assessing them. The objective is to discuss how a careful characterization of different symptoms and signs, and a better translation of preclinical findings may improve our understanding of the complex and entangled mechanisms of neuropathic pain and spasticity.

METHODS

A MEDLINE search was performed using the following terms: 'pain', 'neuropathic', 'spasticity', 'spasms' and 'spinal cord injury'.

RESULTS

This review identified different domains of neuropathic pain and spasticity after SCI and methods to assess them in preclinical and clinical research. Different factors important for pain description include location, onset, pain descriptors and somatosensory function, while muscle tone, spasms, reflexes and clonus are important aspects of spasticity. Similarities and differences between neuropathic pain and spasticity are discussed.

CONCLUSIONS

Understanding that neuropathic pain and spasticity are multidimensional consequences of SCI, and a careful examination and characterization of the symptoms and signs, are a prerequisite for understanding the relationship between neuropathic pain and spasticity and the intricate underlying mechanisms.

Assessments of sensory plasticity after spinal cord injury across species

Spinal cord injury (SCI) is a multifaceted phenomenon associated with alterations in both motor function and sensory function. A majority of patients with SCI report sensory disturbances, including not only loss of sensation, but in many cases enhanced abnormal sensation, dysesthesia and pain. Development of therapeutics to treat these abnormal sensory changes require common measurement tools that can enable cross-species translation from animal models to human patients. We review the current literature on translational nociception/pain measurement in SCI and discuss areas for further development. Although a number of tools exist for measuring both segmental and affective sensory changes, we conclude that there is a pressing need for better, integrative measurement of nociception/pain outcomes across species to enhance precise therapeutic innovation for sensory dysfunction in SCI.