Assessment of Posterior Spinal Cord Function with Electrical Perception Threshold in Spinal Cord Injury

Intra-epidermal electrically evoked potentials are sensitive to detect degenerative cervical myelopathy suggesting their spinothalamic propagation

OBJECTIVE

Degenerative cervical myelopathy (DCM) is a centromedullary spinal cord disorder mainly affecting crossing fibers. While contact heat evoked potentials (CHEPs) are sensitive in detecting DCM by testing spinothalamic integrity, somatosensory evoked potentials (dSSEPs) show unaffected dorsal column conduction. Intra-epidermal electrically evoked potentials (IEEPs) have unknown spinal propagation after noxious stimulation. We investigated (1) the spinothalamic tract propagation and (2) the discriminative power in detecting spinal pathology of IEEPs compared to CHEPs and dSSEPs in DCM.

METHODS

DCM was diagnosed by neurological examination regarding stenosis (MRI). Stimulation of C6, C8, and T4 dermatomes yielded dSSEPs, CHEPs, and IEEPs. (1) Spinal propagation was assessed through concordant or discordant responses, and (2) discriminative power was determined using receiver operating characteristic curves (ROC).

RESULTS

Twenty-seven patients (8F, 56 ± 12yrs) with DCM were analyzed and compared to age-matched healthy controls. IEEPs were abnormal in 43-54%, CHEPs in 37-69%, and dSSEPs in 4-12%. IEEPs showed high concordance with abnormalities of CHEPs (62-69%). ROC analyses showed good discriminative power of CHEPs and IEEPs contrary to dSSEPs.

CONCLUSIONS

The concordance of abnormal responses of CHEPs and IEEPs contrary to dSSEPs suggests spinothalamic propagation of IEEPs.

SIGNIFICANCE

Minimal differences between CHEPs and IEEPs suggest complementary potential by the combined testing of spinothalamic tract integrity.

Combined Neurophysiologic and Neuroimaging Approach to Reveal the Structure-Function Paradox in Cervical Myelopathy

BACKGROUND AND OBJECTIVES

To explore the so-called structure-function paradox in individuals with focal spinal lesions by means of tract-specific MRI coupled with multimodal evoked potentials and quantitative sensory testing.

METHODS

Individuals with signs and symptoms attributable to cervical myelopathy (i.e., no evidence of competing neurologic diagnoses) were recruited at the Balgrist University Hospital, Zurich, Switzerland, between February 2018 and March 2019. We evaluated the relationship between the extent of structural damage within spinal nociceptive pathways (i.e., dorsal horn, spinothalamic tract, anterior commissure) assessed with atlas-based MRI and (1) the functional integrity of spinal nociceptive pathways measured with contact heat-, cold-, and pinprick-evoked potentials and (2) clinical somatosensory phenotypes assessed with quantitative sensory testing.

RESULTS

Sixteen individuals (mean age 61 years) with either degenerative (n = 13) or posttraumatic (n = 3) cervical myelopathy participated in the study. Most individuals presented with mild myelopathy (modified Japanese Orthopaedic Association score >15; n = 13). A total of 71% of individuals presented with structural damage within spinal nociceptive pathways on MRI. However, 50% of these individuals presented with complete functional sparing (i.e., normal contact heat-, cold-, and pinprick-evoked potentials). The extent of structural damage within spinal nociceptive pathways was not associated with functional integrity of thermal (heat: p = 0.57; cold: p = 0.49) and mechano-nociceptive pathways (p = 0.83) or with the clinical somatosensory phenotype (heat: p = 0.16; cold: p = 0.37; mechanical: p = 0.73). The amount of structural damage to the spinothalamic tract did not correlate with spinothalamic conduction velocity (p > 0.05; ρ = -0.11).

DISCUSSION

Our findings provide neurophysiologic evidence to substantiate that structural damage in the spinal cord does not equate to functional somatosensory deficits. This study recognizes the pronounced structure-function paradox in cervical myelopathies and underlines the inevitable need for a multimodal phenotyping approach to reveal the eloquence of lesions within somatosensory pathways.

Application of electrophysiological measures in spinal cord injury clinical trials: a narrative review

STUDY DESIGN

Narrative review.

OBJECTIVES

To discuss how electrophysiology may contribute to future clinical trials in spinal cord injury (SCI) in terms of: (1) improvement of SCI diagnosis, patient stratification and determination of exclusion criteria; (2) the assessment of adverse events; and (3) detection of therapeutic effects following an intervention.

METHODS

An international expert panel for electrophysiological measures in SCI searched and discussed the literature focused on the topic.

RESULTS

Electrophysiology represents a valid method to detect, track, and quantify readouts of nerve functions including signal conduction, e.g., evoked potentials testing long spinal tracts, and neural processing, e.g., reflex testing. Furthermore, electrophysiological measures can predict functional outcomes and thereby guide rehabilitation programs and therapeutic interventions for clinical studies.

CONCLUSION

Objective and quantitative measures of sensory, motor, and autonomic function based on electrophysiological techniques are promising tools to inform and improve future SCI trials. Complementing clinical outcome measures, electrophysiological recordings can improve the SCI diagnosis and patient stratification, as well as the detection of both beneficial and adverse events. Specifically composed electrophysiological measures can be used to characterize the topography and completeness of SCI and reveal neuronal integrity below the lesion, a prerequisite for the success of any interventional trial. Further validation of electrophysiological tools with regard to their validity, reliability, and sensitivity are needed in order to become routinely applied in clinical SCI 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.

Dorsal and ventral horn atrophy is associated with clinical outcome after spinal cord injury

OBJECTIVE

To investigate whether gray matter pathology above the level of injury, alongside white matter changes, also contributes to sensorimotor impairments after spinal cord injury.

METHODS

A 3T MRI protocol was acquired in 17 tetraplegic patients and 21 controls. A sagittal T2-weighted sequence was used to characterize lesion severity. At the C2-3 level, a high-resolution T2*-weighted sequence was used to assess cross-sectional areas of gray and white matter, including their subcompartments; a diffusion-weighted sequence was used to compute voxel-based diffusion indices. Regression models determined associations between lesion severity and tissue-specific neurodegeneration and associations between the latter with neurophysiologic and clinical outcome.

RESULTS

Neurodegeneration was evident within the dorsal and ventral horns and white matter above the level of injury. Tract-specific neurodegeneration was associated with prolonged conduction of appropriate electrophysiologic recordings. Dorsal horn atrophy was associated with sensory outcome, while ventral horn atrophy was associated with motor outcome. White matter integrity of dorsal columns and corticospinal tracts was associated with daily-life independence.

CONCLUSION

Our results suggest that, next to anterograde and retrograde degeneration of white matter tracts, neuronal circuits within the spinal cord far above the level of injury undergo transsynaptic neurodegeneration, resulting in specific gray matter changes. Such improved understanding of tissue-specific cord pathology offers potential biomarkers with more efficient targeting and monitoring of neuroregenerative (i.e., white matter) and neuroprotective (i.e., gray matter) agents.

Afferent input and sensory function after human spinal cord injury

Spinal cord injury (SCI) often disrupts the integrity of afferent (sensory) axons projecting through the spinal cord dorsal columns to the brain. Examinations of ascending sensory tracts, therefore, are critical for monitoring the extent of SCI and recovery processes. In this review, we discuss the most common electrophysiological techniques used to assess transmission of afferent inputs to the primary motor cortex (i.e., afferent input-induced facilitation and inhibition) and the somatosensory cortex [i.e., somatosensory evoked potentials (SSEPs), dermatomal SSEPs, and electrical perceptual thresholds] following human SCI. We discuss how afferent input modulates corticospinal excitability by involving cortical and spinal mechanisms depending on the timing of the effects, which need to be considered separately for upper and lower limb muscles. We argue that the time of arrival of afferent input onto the sensory and motor cortex is critical to consider in plasticity-induced protocols in humans with SCI. We also discuss how current sensory exams have been used to detect differences between control and SCI participants but might be less optimal to characterize the level and severity of injury. There is a need to conduct some of these electrophysiological examinations during functionally relevant behaviors to understand the contribution of impaired afferent inputs to the control, or lack of control, of movement. Thus the effects of transmission of afferent inputs to the brain need to be considered on multiple functions following human SCI.

Time-Dependent Discrepancies between Assessments of Sensory Function after Incomplete Cervical Spinal Cord Injury

We recently demonstrated that the electrical perceptual threshold (EPT) examination reveals spared sensory function at lower spinal segments compared with the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) examination in humans with chronic incomplete cervical spinal cord injury (SCI). Here, we investigated whether discrepancies in sensory function detected by both sensory examinations change over time after SCI. Forty-five participants with acute (<1 year), chronic (≥1-10 years), and extended-chronic (>10 years) incomplete cervical SCI and 30 control subjects were tested on dermatomes C2-T4 bilaterally. EPT values were higher in subjects with acute (2.5 ± 0.8 mA), chronic (2.2 ± 0.7 mA), or extended-chronic (2.8 ± 1.1 mA) SCI compared with controls (1.0 ± 0.1 mA). The EPT examination detected sensory impairments in spinal segments above (2.3 ± 0.9) and below (4.2 ± 2.6) the level detected by the ISNCSCI sensory examination in participants with acute and chronic SCI, respectively. Notably, both examinations detected similar levels of spared sensory function in the extended-chronic phase of SCI (0.8 ± 0.5). A negative correlation was found between differences in EPT and ISNCSCI sensory levels and time post-injury. These observations indicate that discrepancies between EPT and ISNCSCI sensory scores are time-dependent, with the EPT revealing impaired sensory function above, below, or at the same spinal segment as the ISNCSCI examination. We propose that the EPT is a sensitive tool to assess changes in sensory function over time after incomplete cervical SCI.

Discrepancies between clinical assessments of sensory function and electrical perceptual thresholds after incomplete chronic cervical spinal cord injury

Study Design

Prospective experimental.

Objectives

To compare sensory function as revealed by light touch and pin prick tests of the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) and the electrical perceptual threshold (EPT) exams in individuals with chronic incomplete cervical spinal cord injury (SCI).

Setting

Pittsburgh, United States.

Methods

EPT was tested using cutaneous electrical stimulation (0.5 ms pulse width, 3 Hz) in 32 healthy controls and in 17 participants with SCI over key points on dermatomes C2 to T4 on each side of the body. Light touch and pin prick ISNCSCI scores were tested at the same key dermatomes in SCI participants.

Results

In controls, EPT values were higher in older males (1.26±0.2 mA, mean±s.d.) compared with younger males (1.0±0.2 mA) and older females (0.9±0.2 mA), regardless of the dermatome and side tested. Fifteen out of seventeen SCI participants showed that the level of sensory impairment detected by the EPT was below the level detected by the ISNCSCI (mean=4.5±2.4, range 1–9). The frequency distribution of EPTs was similar to older male controls in dermatomes above but not below the ISNCSCI sensory level. The difference between EPT and ISNCSCI sensory level was negatively correlated with the time post injury.

Conclusions

The results show that, in the chronic stage of cervical SCI, the EPT reveals spared sensory function at lower (~5) spinal segments than the ISNCSCI sensory exam. It is hence found that the EPT is a sensitive tool to assess recovery of sensory function after chronic SCI.

Effectiveness of High-Frequency Electrical Stimulation Following Sensitization With Capsaicin

Although nonnoxious, high-frequency electrical stimulation applied segmentally (ie, conventional transcutaneous electrical nerve stimulation [TENS]) has been proposed to modulate pain, the mechanisms underlying analgesia remain poorly understood. To further elucidate how TENS modulates pain, we examined evoked responses to noxious thermal stimuli after the induction of sensitization using capsaicin in healthy volunteers. We hypothesized that sensitization caused by capsaicin application would unmask TENS analgesia, which could not be detected in the absence of sensitization. Forty-nine healthy subjects took part in a series of experiments. The experiments comprised the application of topical capsaicin (.075%) on the left hand in the C6 dermatome, varying the location of TENS (segmental, left C6 dermatome, vs extrasegmental, right shoulder), and assessing rating of perception (numeric rating scale: 0-10) and evoked potentials to noxious contact heat stimuli. The extrasegmental site was included as a control condition because previous studies indicate no analgesic effect to remote conventional TENS. Conventional TENS had no significant effect on rating or sensory evoked potentials in subjects untreated with capsaicin. However, segmental TENS applied in conjunction with capsaicin significantly reduced sensation to noxious thermal stimuli following a 60-minute period of sensitization.

PERSPECTIVE

The study indicates that sensitization with capsaicin unmasks the analgesic effect of conventional TENS on perception of noxious contact heat stimuli. Our findings indicate that TENS may be interacting segmentally to modulate distinct aspects of sensitization, which in turn results in analgesia to thermal stimulation.

Spinal cord injury: how can we improve the classification and quantification of its severity and prognosis?

The preservation of functional neural tissue after spinal cord injury (SCI) is the basis for spontaneous neurological recovery. Some injured patients in the acute phase have more potential for recovery than others. This fact is problematic for the construction of clinical trials because enrollment of subjects with variable recovery potential makes it difficult to detect effects, requires large sample sizes, and risks Type II errors. In addition, the current methods to assess injury and recovery are non-quantitative and not sensitive. It is likely that therapeutic combinations will be necessary to cause substantially improved function after SCI, thus we need highly sensitive techniques to evaluate changes in motor, sensory, autonomic and other functions. We review several emerging neurophysiological techniques with high sensitivity. Quantitative methods to evaluate residual tissue sparing after severe acute SCI have not entered widespread clinical use. This reduces the ability to correlate structural preservation with clinical outcome following SCI resulting in enrollment of subjects with varying patterns of tissue preservation and injury into clinical trials. We propose that the inclusion of additional measures of injury severity, pattern, and individual genetic characteristics may enable stratification in clinical trials to make the testing of therapeutic interventions more effective and efficient. New imaging techniques to assess tract injury and demyelination and methods to quantify tissue injury, inflammatory markers, and neuroglial biochemical changes may improve the evaluation of injury severity, and the correlation with neurological outcome, and measure the effects of treatment more robustly than is currently possible. The ability to test such a multimodality approach will require a high degree of collaboration between clinical and research centers and government research support. When the most informative of these assessments is determined, it may be possible to identify patients with substantial recovery potential, improve selection criteria and conduct more efficient clinical trials.

Diagnostic use of dermatomal somatosensory-evoked potentials in spinal disorders: Case series

OBJECTIVE/CONTEXT: Dermatomal somatosensory-evoked potentials (dSEPs) may be valuable for diagnostic purposes in selected cases with spinal disorders.

DESIGN

Reports on cases with successful use of dSEPs.

FINDINGS

Cases 1 and 2 had lesions causing multiple root involvement (upper to middle lumbar region in Case 1 and lower sacral region in Case 2). Cystic lesions in both cases seemed to compress more than one nerve root, and stimulation at the center of the involved dermatomes in dSEPs helped to reveal the functional abnormality. Cases 3 and 4 had lesions involving the spinal cord with or without nerve root impairment. In Case 3, an magnetic resonance imaging (MRI)-verified lesion seemed to occupy a considerable volume of the lower spinal cord, causing only very restricted clinical sensory and motor signs. In Case 4, a cervical MRI showed a small well-circumscribed intramedullary lesion at right C2 level. All neurophysiological investigations were normal in the latter two patients (motor, tibial, and median somatosensory-evoked potentials in Case 3, and electromyography in both) except for the dSEPs.

CONCLUSIONS

Objectifying the presence and degree of sensory involvement in spinal disorders may be helpful for establishing diagnoses and in therapeutic decision-making. Valuable information could be provided by dSEPs in selected patients with multiple root or spinal cord involvement.

Improved diagnosis of spinal cord disorders with contact heat evoked potentials

Objective:

To evaluate the sensitivity of contact heat evoked potentials (CHEPs) compared with dermatomal somatosensory evoked potentials (dSSEPs) and clinical sensory testing in myelopathic spinal cord disorders (SCDs).

Methods:

In a prospective cohort study, light-touch (LT) and pinprick (PP) testing was complemented by dermatomal CHEPs and dSSEPs in patients with a confirmed SCD as defined by MRI. Patients with different etiologies (i.e., traumatic and nontraumatic) and varying degrees of spinal cord damage (i.e., completeness) were included. SCD was distinguished into 3 categories according to MRI pattern and neurologic examination: a) complete, b) incomplete-diffuse, and c) central or anterior cord damage.

Results:

Seventy-five patients were included (complete n = 7, incomplete-diffuse n = 33, central/anterior n = 35). In total, 319 dermatomes were tested with combined CHEPs and dSSEPs. CHEPs, dSSEPs, and clinical sensory testing were comparably sensitive to detect the myelopathy in complete (CHEPs 100%, dSSEPs 91%, PP and LT 82%) and incomplete-diffuse (CHEPs 92%, dSSEPs and PP 86%, LT 81%, p > 0.05 for all comparisons) cord damage. In central/anterior cord damage, CHEPs showed a significantly higher sensitivity than dSSEPs (89% compared with 24%, p < 0.001) and clinical sensory testing (PP 62%, LT 57%, p < 0.05). A subclinical sensory impairment was detected more frequently by CHEPs than dSSEPs (60% compared with 29%, p = 0.001).

Conclusions:

Assessment of spinothalamic pathways with CHEPs is reliable and revealed the highest sensitivity in all SCDs. Specifically in incomplete lesions that spare dorsal pathways, CHEPs are sensitive to complement the clinical diagnosis.

Reliability of the electrical perceptual threshold and Semmes-Weinstein monofilament tests of cutaneous sensibility

STUDY DESIGN

Prospective experimental.

OBJECTIVES

To compare the reliability and repeatability of the electrical perceptual threshold (EPT) and Semmes-Weinstein monofilament (SWM) tests for cutaneous sensibility. EPT and SWM tests have potential as quantitative and sensitive adjuncts to the American Spinal Injuries Association (ASIA) Impairment Scale (AIS) assessment of spinal cord injury (SCI).

SETTING

London, UK.

METHODS

EPT and SWM tests were carried out on 40 neurologically healthy individuals (20 male). One examiner carried out all the tests. Each individual was examined for EPT and SWM sensitivity at ASIA key points on four dermatomes (C4, T1, T6, L4) on both sides of the body. The tests were repeated after an interval of approximately 1 week. Intra-rater reliability was determined using intra-class correlation coefficients (ICC). Repeatability was determined using the method of Bland and Altman.

RESULTS

There were no significant differences in the mean values of EPT or SWM between assessments for any dermatome. Significant difference in mean values for both EPT and SWM were observed between some dermatomes. ICC ranged from 0.67 to 0.81 for the EPT and from 0.46 to 0.61 for the SWM. Higher ICC for the EPT compared with the SWM was again revealed when male and female subjects were assessed separately. Correlation between EPT and SWM was weak or (largely) absent.

CONCLUSION

EPT has better reliability than SWM in healthy subjects. However, as both tests have the potential to add sensitivity and resolution to the AIS assessment, a further comparison of their repeatability in SCI is warranted.

Refined sensory measures of neural repair in human spinal cord injury: bridging preclinical findings to clinical value

Sensory input from the periphery to the brain can be severely compromised or completely abolished after an injury to the spinal cord. Evidence from animal models suggests that endogenous repair processes in the spinal cord mediate extensive sprouting and that this might be further attenuated by targeted therapeutic interventions. However, the extent to which sprouting can contribute to spontaneous recovery after human spinal cord injury (SCI) remains largely unknown, in part because few measurement tools are available in order to non-invasively detect subtle changes in neurophysiology. The proposed application of segmental sensory evoked potentials (e.g., dermatomal contact heat evoked potentials and somatosensory evoked potentials) to assess conduction in ascending pathways (i.e., spinothalamic and dorsal column, respectively) differs from conventional approaches in that individual spinal segments adjacent to the level of lesion are examined. The adoption of these approaches into clinical research might provide improved resolution for measuring changes in sensory impairments and might determine the extent by which spontaneous recovery after SCI is mediated by similar endogenous repair mechanisms in humans as in animal models.

Clinical neurophysiology in the prognosis and monitoring of traumatic spinal cord injury

Preclinical studies for the repair of spinal cord injury (SCI) and potential therapies for accessing the inherent plasticity of the central nervous system (CNS) to promote recovery of function are currently moving into the translational stage. These emerging clinical trials of therapeutic interventions for the repair of SCI require improved assessment techniques and quantitative outcome measures to supplement the American Spinal Injuries Association (ASIA) Impairment Scales. This chapter attempts to identify those electrophysiological techniques that show the most promise for provision of objective and quantitative measures of sensory, motor, and autonomic function in SCI. Reviewed are: (1) somatosensory evoked potentials, including dermatomal somatosensory evoked potentials, and the electrical perceptual threshold as tests of the dorsal (posterior) column pathway; (2) laser evoked potentials and contact heat evoked potentials as tests of the anterior spinothalamic tract; (3) motor evoked potentials in limb muscles, in response to transcranial magnetic stimulation of the motor cortex as tests of the corticospinal tract, and the application of the technique to assessment of trunk and sphincter muscles; and (4) the sympathetic skin response as a test of spinal cord access to the sympathetic chain.

Changes in Electrical Perception Threshold Within the First 6 Months After Traumatic Spinal Cord Injury

Objective. To assess the reliability of the electrical perception threshold (EPT) in healthy participants and its responsiveness in patients for 6 months after traumatic spinal cord injury (SCI). Methods. The reliability of EPT measures was assessed in 15 healthy volunteers (from C3 to S2). EPT measures were assessed in 37 patients at 1, 3, and 6 months after SCI. EPT was determined in dermatomes at, above, and below the neurological level of lesion. Reliability was quantified with an intraclass correlation coefficient (ICC) and responsiveness with the standardized response mean (SRM). Dermatomes were classified as having normal or pathological sensory perception, based on both light touch (LT) and EPT testing. The percentage of agreement between LT and EPT classifications was determined. Results. The ICCs varied considerably between dermatomes (0.00 ≤ ICC ≤ 0.86). Overall, EPTs changed little within the first 6 months after SCI, resulting in small SRM values. Agreement between classifications according to EPT or LT testing varied from 30% to 100%. The least agreement was observed in the first segment below the lesion. Conclusion. Future studies must note that the reliability of EPT differs between dermatomes in healthy participants. Furthermore, at and below the level of the lesion, spontaneous recovery of sensory perception is poor within the first 6 months after SCI. Based on subgroup analyses, if a translational trial aims to improve sensory perception around the level of the lesion, sensory-incomplete tetraplegic patients could be included. These patients show poor spontaneous recovery, and the EPT may detect subtle changes in perception.

Changes in electrical perceptual threshold in the first 6 months following spinal cord injury

OBJECTIVES

To investigate the use of electrical perceptual threshold (EPT) testing to follow the natural history of sensory progression after complete and incomplete acute spinal cord injury (SCI) and to compare EPT changes with the American Spinal Injuries Association (ASIA) Impairment Scale (AIS).

STUDY DESIGN

Prospective descriptive study.

METHODS

ASIA examination and EPT testing was performed on 17 patients (7 AIS A, 10 AIS B-D), within 1, 3, and 6 months after acute SCI. EPT assessment was carried out bilaterally at ASIA sensory points from 2 levels above the neurological level to all levels below, including the sacral segments. Comparisons of EPT values above, at, and below the SCI were made at the three time points as well as comparisons of EPT data to ASIA assessment.

RESULTS

There was poor agreement between lowest normal level on EPT and ASIA assessment. Over time, EPTs tended to deteriorate above and at the ASIA level in AIS A patients with modest changes below the neurological level of injury (NLI), mainly where EPTs correlated with the zone of partial preservation. Sacral sparing was detected in one patient with EPT testing, but not with ASIA assessment. AIS B-D patients showed improvement at the ASIA level and extensive changes, both improvement and deterioration, below the NLI.

CONCLUSION

EPT testing has sufficient sensitivity to detect subclinical changes in sensory function as early as the first month post-SCI, which is not apparent in ASIA examination. In particular, the testing is able to show abnormalities at and around the injury site for both complete and incomplete SCI. In addition, EPT allows for the detection and monitoring of alterations, both improvements and deterioration, in the abnormal range of sensation.

The impact of sacral sensory sparing in motor complete spinal cord injury

OBJECTIVE

To determine the effect of sensory sparing in motor complete persons with spinal cord injury (SCI) on completion of rehabilitation on neurologic, functional, and social outcomes reported at 1 year.

DESIGN

Secondary analysis of longitudinal data collected by using prospective survey-based methods.

SETTING

Data submitted to the National SCI Statistical Center Database.

PARTICIPANTS

Of persons (N=4106) enrolled in the model system with a motor complete injury (American Spinal Injury Association Impairment Scale [AIS] grade A or B) at the time of discharge between 1997 and 2007, a total of 2331 (56.8%) completed a 1-year follow-up interview (Form II) and 1284 (31.3%) had complete data for neurologic (eg, AIS grade, injury level) variables at 1 year.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

AIS grade (A vs B) at 1 year, bladder management, hospitalizations, perceived health status, motor FIM items, Satisfaction With Life Scale, depressive symptoms, and social participation.

RESULTS

Compared with persons with AIS grade A at discharge, persons with AIS grade B were less likely to require indwelling catheterization and be hospitalized and more likely to perceive better health, report greater functional independence (ie, self-care, sphincter control, mobility, locomotion), and report social participation in the first year postinjury. A greater portion of individuals with AIS grade B at discharge had improved neurologic recovery at 1 year postinjury than those with AIS grade A. Significant AIS group differences in 1-year outcomes related to physical health were maintained after excluding persons who improved to motor incomplete status for only bladder management and change in perceived health status. This recognition of differences between persons with motor complete injuries (AIS grade A vs B) has important ramifications for the field of SCI rehabilitation and research.

Age, gender, and side differences of cutaneous electrical perceptual threshold testing in an able-bodied population

OBJECTIVE

To investigate age, gender, and left-right differences in cutaneous electrical perceptual threshold (EPT) testing in an able-bodied, Australian sample.

STUDY DESIGN

Prospective experimental.

SETTING

Hospital-based spinal cord injuries unit.

METHODS

Cutaneous electrical stimulation of the 28 dermatomes at ASIA sensory key points (C2-S4/S5) was performed on 29 female and 16 male healthy volunteers aged 21 to 76 years. Mean EPTs for each dermatome were compared (repeated measures ANOVA) for left-right, gender-related, and age-related (</ >50 years of age) differences.

RESULTS

There was no group difference between sides (repeated measures ANOVA, P = 0.934). Women across all ages had lower group mean EPTs than men (P < 0.0001). Women younger than age 50 years had lower mean EPTs than those older than age 50 years (P = 0.008). There was no group difference between younger and older men (P = 0.371). Analysis of individual dermatomes revealed no significant differences in thoracic dermatomes between genders or age groups, contrary to the limb dermatomes.

CONCLUSION

There were gender differences in EPT values across all ages. Women had higher EPTs as they advanced in age, but this was less clear in men. There was considerable somatotopic variability in EPTs, especially in the lower limbs. If EPT testing is to be applied to detect subclinical changes within a dermatome, establishment of age- and gender-specific somatotopic normograms is a prerequisite.

Dermatomal Somatosensory Evoked Potentials and Electrical Perception Thresholds During Recovery From Cervical Spinal Cord Injury

Background. Dermatomal somatosensory evoked potentials (dSSEPs) not only provide a neurophysiological readout comparable with conventional SSEPs but also provide an opportunity to track changes in sensory function corresponding to individual dermatomes (ie, a single spinal segment) above, at, and below the level of spinal cord injury (SCI). Objectives. This study aimed to determine the reliability and responsiveness of dSSEPs and electrical perception thresholds (EPTs) to monitor changes in sensory function after cervical SCI. Methods. Initial and follow-up dSSEPs and EPTs were recorded from cervical dermatomes (C4-C8) of patients with traumatic tetraplegia (C3-C8; ASIA Impairment Scale A-D) during recovery after SCI (n = 18). Results. Follow-up examination of 74 initial dSSEPs unaffected by SCI (n = 18) revealed no significant change in latency (Δ = 0.0 ± 1.4 ms; P = .9) or EPT sensitivity (Δ = 0.1 ± 0.8 mA; P = .3). In 41 dSSEPs initially delayed after SCI (n = 14), latencies significantly decreased on follow-up examination (Δ = -3.1 ± 2.9 ms; P < .01) without a corresponding increase in sensitivity of the EPT (Δ = 0.2 ± 3.4 mA; P = .7). dSSEPs that were not measurable initially were subsequently recorded in 11 dermatomes (n = 5) on follow-up examination. This conversion of abolished-to-recordable dSSEPs was often preceded by the perception of an initial EPT and associated with a concomitant recovery of EPT at follow-up. Conclusion. dSSEPs and EPT can be reliably recorded to monitor changes in sensory function for each individual spinal segment after cervical SCI. dSSEPs may be potentially useful to monitor the safety of a therapeutic drug or cell transplant in early-phase (I/II) clinical trials as well as document the potential efficacy of interventions where the standard neurological assessment might not detect subtle therapeutic effects.

A quantitative skin impedance test to diagnose spinal cord injury

The purpose of this study was to develop a quantitative skin impedance test that could be used to diagnose spinal cord injury (SCI) if any, especially in unconscious and/or non-cooperative SCI patients. To achieve this goal, initially skin impedance of the sensory key points of the dermatomes (between C3 and S1 bilaterally) was measured in 15 traumatic SCI patients (13 paraplegics and 2 tetraplegics) and 15 control subjects. In order to classify impedance values and to observe whether there would be a significant difference between patient and subject impedances, an artificial neural network (ANN) with back-propagation algorithm was employed. Validation results of the ANN showed promising performance. It could classify traumatic SCI patients with a success rate of 73%. By assessing the experimental protocols and the validation results, the proposed method seemed to be a simple, objective, quantitative, non-invasive and non-expensive way of assessing SCI in such patients.

Neuropathic pain in spinal cord injury: significance of clinical and electrophysiological measures

A large percentage of spinal cord-injured subjects suffer from neuropathic pain below the level of the lesion (bNP). The neural mechanisms underlying this condition are not clear. The aim of this study was to elucidate the general effects of spinal deafferentiation and of bNP on electroencephalographic (EEG) activity. In addition, the relationship between the presence of bNP and impaired function of the spinothalamic tract was studied. Measurements were performed in complete and incomplete spinal cord-injured subjects with and without bNP as well as in a healthy control group. Spinothalamic tract function, assessed by contact heat evoked potentials, did not differ between subjects with and without bNP; nevertheless, it was impaired in 94% of subjects suffering from bNP. In the EEG recordings, the degree of deafferentiation was reflected in a slowing of EEG peak frequency in the 6-12-Hz band. Taking into account this unspecific effect, spinal cord-injured subjects with bNP showed significantly slower EEG activity than subjects without bNP. A discrimination analysis in the subjects with spinothalamic tract dysfunction correctly classified 84% of subjects as belonging to either the group with bNP or the group without bNP, according to their EEG peak frequency. These findings could be helpful for both the development of an objective diagnosis of bNP and for testing the effectiveness of new therapeutic agents.

Electrophysiological outcomes after spinal cord injury

Electrophysiological measures can provide information that complements clinical assessments such as the American Spinal Injury Association sensory and motor scores in the evaluation of outcomes after spinal cord injury (SCI). The authors review and summarize the literature regarding tests that are most relevant to the study of SCI recovery--in particular, motor evoked potentials and somatosensory evoked potentials (SSEPs). In addition, they discuss the role of other tests, including F-wave nerve conductance tests and electromyography, sympathetic skin response, and the Hoffman reflex (H-reflex) test as well as the promise of dermatomal SSEPs and the electrical perceptual threshold test, newer quantitative tests of sensory function. It has been shown that motor evoked potential amplitudes improve with SCI recovery but latencies do not. Somatosensory evoked potentials are predictive of ambulatory capacity and hand function. Hoffman reflexes are present during spinal shock despite the loss of tendon reflexes, but their amplitudes increase with time after injury. Further, H-reflex modulation is reflective of changes in spinal excitability. While these tests have produced data that is congruent with clinical evaluations, they have yet to surpass clinical evaluations in predicting outcomes. Continuing research using these methodologies should yield a better understanding of the mechanisms behind SCI recovery and thus provide potentially greater predictive and evaluative power.