John L. K. Kramer

Relationship Between Clinical Assessments of Function and Measurements From an Upper-Limb Robotic Rehabilitation Device in Cervical Spinal Cord Injury

Upper limb robotic rehabilitation devices can collect quantitative data about the users movements. Identifying relationships between robotic sensor data and manual clinical assessment scores would enable more precise tracking of the time course of recovery after injury and reduce the need for time-consuming manual assessments by skilled personnel. This study used measurements from robotic rehabilitation sessions to predict clinical scores in a traumatic cervical spinal cord injury (SCI) population. A retrospective analysis was conducted on data collected from subjects using the Armeo Spring (Hocoma, AG) in three rehabilitation centers. Fourteen predictive variables were explored, relating to range-of-motion, movement smoothness, and grip ability. Regression models using up to four predictors were developed to describe the following clinical scores: the GRASSP (consisting of four sub-scores), the ARAT, and the SCIM. The resulting adjusted R^2 value was highest for the GRASSP “Quantitative Prehension” component (0.78), and lowest for the GRASSP “Sensibility” component (0.54). In contrast to comparable studies in stroke survivors, movement smoothness was least beneficial for predicting clinical scores in SCI. Prediction of upper-limb clinical scores in SCI is feasible using measurements from a robotic rehabilitation device, without the need for dedicated assessment procedures.

Assessment of posterior spinal cord function with electrical perception threshold in spinal cord injury.

The objective of this study was to evaluate the relevant sensory spinal pathways involved in conveying conduction of electrical perceptual threshold (EPT). In 34 individuals with cervical spinal cord injury (SCI) and eight healthy control subjects, combined EPT and electrical pain perception (EPP), and dermatomal somatosensory evoked potentials (dSSEP) from cervical dermatomes were examined. Stimulation intensities for EPT were recorded to determine quantitative sensory perception and related neurophysiological dSSEP interpretation of posterior spinal cord conduction based on onset latency and waveform configuration. The preservation of EPP in dermatomes was examined relative to EPT to dissociate the involvement of the posterior (dorsal horn and ascending dorsal column) and anterior (decussating and ascending spinothalamic fibers) spinal cord according to different nerve fiber recruitment in the periphery. Pathological EPT values were significantly (p < 0.05) accurate at predicting pathological and abolished dSSEP recordings (>80%), and the mean EPT of pathological and abolished dSSEPs was significantly (p < 0.05) increased compared to non-affected and control dSSEPs. dSSEPs demonstrated normal early onset latency at perceptually low stimulation intensities (<2.5 mA), and selectively absent EPP was dissociated from preserved EPT and/or dSSEP in 22.2% of dermatomes with incomplete sensory deficit. The relationship between EPT and dSSEP interpretation, dSSEP early onset latency and perceptual stimulation intensity, and the dissociation of EPT from EPP suggests that EPT is conducted within the posterior spinal cord. The combination of EPT and EPP with dSSEPs provides reliable quantitative sensory information to assess the segmental integrity of the posterior and anterior spinal cord, and may improve the sensitivity to monitor changes in sensory function after SCI.

Test-retest reliability of contact heat-evoked potentials from cervical dermatomes.

Summary The purpose of this study was to investigate the test–retest reliability of contact heat-evoked potentials (CHEPs) in neurologically healthy subjects from cervical dermatomes (C4–C8). Seventeen individuals underwent test–retest examination of cervical CHEPs. Peak latencies and peak-to-peak amplitude of N2–P2 and ratings of perceived intensity were analyzed using test–retest reliability statistics (intraclass correlation coefficients [ICCs] and Bland–Altman confidence parameters). For comparison, a group of similar age and gender was also examined with dermatomal somatosensory-evoked potentials (dSSEPs, n = 17). The ICC values for CHEP latency and amplitude parameters were significant (P < 0.05) and corresponded to at least “fair” reliability, while peak-to-peak amplitude demonstrated “substantial” (≥0.81) reliability for all dermatomes. The coefficients of repeatability (i.e., 2SD of the difference between examinations) confirm that CHEPs and dSSEPs are reliable according to measures of latency. Superior peak-to-peak amplitude test–retest reliability was found for CHEPs. In conclusion, the test–retest reliability of dSSEP and CHEP parameters supports the fact that these outcomes can be used to objectively track changes in spinal conduction in the dorsal column and spinothalamic tract, respectively. The reliable acquisition of CHEPs may depend on the intensity of the sensation reported by the subject for a given area of skin stimulated.

Improving the acquisition of nociceptive evoked potentials without causing more pain

Summary Causing a greater subjective pain experience is not necessary for improving the objective assessment of pain using contact heat‐evoked potentials. ABSTRACT Following nociceptive heat or laser stimulation, an early contralateral and later vertex potential can be recorded. Although more indicative of the nociceptive input, the acquisition of the contralateral N1 after contact heat stimulation (contact heat‐evoked potentials [CHEPs]) remains difficult. An advantage of contact heat is that the baseline skin temperature preceding peak stimulation can be controlled. Increasing the baseline temperature may represent a novel strategy to improve the acquisition of CHEPs without resulting in more subjective pain to stimulation. A study was undertaken in 23 healthy subjects to examine the effects of increasing the baseline temperature but not the perceived intensity of contact heat stimulation. A combined standard averaging and single‐trial analysis was performed to disclose how changes in averaged waveforms related to latency jitter and individual trial amplitudes. By increasing the baseline temperature, the acquisition of N1 was improved among subjects with a low‐amplitude response (greater than −4 μV) following 35°C baseline temperature stimulation (P < .05). Based on standard averaging, N2/P2 amplitudes were also significantly increased with and without an accompanying change in the rating of perceived pain when the baseline temperature was increased (P < .05). In contrast, automated single‐trial averaging revealed no significant difference in N2 amplitude when the baseline temperature was increased to 42°C and the peak temperature reduced. These findings suggest that 2 mechanisms underlie the improved acquisition of CHEPs: increased synchronization of afferent volley, yielding larger‐amplitude evoked potentials in response to the same rating of intensity; and reduced inter‐trial variability.

Assessment of Spinothalamic Tract Function Beyond Pinprick in Spinal Cord Lesions A Contact Heat Evoked Potential Study

Background. Although a mainstay of clinical sensory examination after damage in the spinal cord, pinprick sensation represents only one afferent modality conveyed in the spinothalamic tract. As an objective outcome, complementary information regarding spinothalamic tract conduction may be elucidated by measuring contact heat evoked potentials (CHEPs). Objective. To assess the value of CHEPs to measure spinothalamic tract function in spinal cord disorders compared with pinprick scoring. Methods. CHEPs were examined using a standard (35°C) and increased baseline (42°C) contact heat temperature. Pinprick sensation was rated as absent, impaired, or normal according to the International Standards for the Neurological Classification of Spinal Cord Injury. Results. Fifty-nine dermatomes above, at, and below the sensory level of impairment were analyzed in 37 patients with defined spinal cord disorder. In dermatomes with absent or impaired pinprick sensation, CHEPs using a standard baseline temperature were mainly abolished (3/16 and 8/35, respectively). However, when applying an increased baseline temperature, CHEPs became recordable (absent: 11/16; impaired: 31/35). Furthermore, CHEPs with increased baseline temperature allowed discerning between dermatomes with absent, impaired, and normal pinprick sensation when using an objective measure (ie, N2P2 amplitude). In contrast, the pain perception to contact heat stimulation was independent of pinprick scores. Conclusion. Applying pinprick testing is of limited sensitivity to assess spinothalamic tract function in spinal cord disorders. The application of CHEPs (using standard and increased baseline temperatures) as an objective readout provides complementary information of spinothalamic tract functional integrity beyond pinprick testing.

Differences in spinothalamic function of cervical and thoracic dermatomes: insights using contact heat evoked potentials.

Introduction: After spinal cord injury, contact heat evoked potentials (CHEPs) may represent a means to refine the clinical assessment of sensory function from each spinal cord segment by quantifying nociception, including conduction along the spinothalamic tract. Methods: The influence of stimulation site (i.e., dermatomes) on CHEPs and thermal thresholds in 19 healthy subjects (mean age, 45.2 ± 18.3 years) divided into 2 age classes (younger subjects, n = 10; mean age, 28.8 ± 5.2 years; older subjects, n = 9; mean age, 63.4 ± 3.4 years) at 5 different dermatomes (C4, C5, C6, C8, and T4) was assessed. Results: In terms of distance from the body midline (i.e., spinal cord entry), there was a reduction in CHEP amplitudes from proximal (C4 and T4) to distal (C6 and C8) dermatomes with a corresponding reduction in nociceptive perception (i.e., pain threshold and rating). Within primary and secondary cortical sensory areas, including areas associated with affective noxious processing, the cortical source density analysis showed a similar current density distribution between C4 and C8 dermatomes but consistent higher current densities for C4. Conclusions: The study supports CHEPs as a feasible tool for assessing discrete dermatomes corresponding to spinal cord segments. The results suggest that the proximodistal pattern in the intensity of perceived pain and CHEP amplitudes is likely attributable to the distribution of heat nociceptors and the increase in conduction distance from proximal to distal dermatomes. The present findings emphasize on the importance that if patients are assessed segment by segment, the underlying topographical differences need to be accounted for.

Differences in cortical coding of heat evoked pain beyond the perceived intensity: An fMRI and EEG study

Imaging studies have identified a wide network of brain areas activated by nociceptive stimuli and revealed differences in somatotopic representation of highly distinct stimulation sites (foot vs. hand) in the primary (S1) and secondary (S2) somatosensory cortices. Somatotopic organization between adjacent dermatomes and differences in cortical coding of similarly perceived nociceptive stimulation are less well studied. Here, cortical processing following contact heat nociceptive stimulation of cervical (C4, C6, and C8) and trunk (T10) dermatomes were recorded in 20 healthy subjects using functional magnetic resonance imaging (fMRI) and electroencephalography (EEG). Stimulation of T10 compared with the C6 and C8 revealed significant higher response intensity in the left S1 (contralateral) and the right S2 (ipsilateral) even when the perceived pain was equal between stimulation sites. Accordingly, contact heat evoked potentials following stimulation of T10 showed significantly higher N2P2 amplitudes compared to C6 and C8. Adjacent dermatomes did not reveal a distinct somatotopical representation. Within the assessed cervical and trunk dermatomes, nociceptive cortical processing to heat differs significantly in magnitude even when controlling for pain perception. This study provides evidence that controlling for pain perception is not sufficient to compare directly the magnitude of cortical processing [blood oxygen level dependence (BOLD) response and amplitude of evoked potentials] between body sites. Hum Brain Mapp 35:1379–1389, 2014.

An Objective Measure of Stimulus-Evoked Pain

For most clinical assessments, reporting perception of a painful event has relied on subjective ratings [e.g., the visual analog scale (VAS)]. A more quantifiable and objective method is desirable, preferably one that is directly related to the physiological processing of nociceptive stimuli. An

Thoracic disc herniation in a patient with tethered cord and lumbar syringomyelia and diastematomyelia: magnetic resonance imaging and neurophysiological findings

Study Design. Case report. Objective. To describe the diagnostic challenges in a patient suffering from thoracic disc herniation (TDH) and spina bifida complicated by multiple lumbar spinal cord abnormalities, i.e., tethered cord, lumbar syringomyelia, and diastematomyelia. Summary of Background Data. Advances in neuroimaging, i.e., magnetic resonance imaging, increase the sensitivity to disclose both clinically relevant but also other spine and spinal cord abnormalities. TDH accounts for less than 1% of all surgically treated disc herniations. Syringomyelia and diastematomyelia are comparably rare and present with varying degrees of spinal cord dysfunction. Methods. A 54-year-old women presented with progressive pain and sensorimotor symptoms in the lower back and limbs. Neurologic examination revealed lower limb spastic motor deficits and spinal ataxia. Magnetic resonance imaging revealed a T6–T7 disc herniation, with spinal cord signal change in addition to a spina bifida with sacral tethered cord, lumbar syringomyelia, and diastematomyelia. Combined neurophysiological testing identified a neurologic lesion in the mid thoracic cord, with normal lower limb nerve conduction and reflex recordings, but pathologic somatosensory-evoked potential and T6 paravertebral electromyography. Results. The patient was diagnosed with a clinically relevant T6–T7 disc herniation and underwent successful surgical decompression resulting in electrophysiological improvements. Conclusion. This unique case highlights the value of electrophysiology in the evaluation of a complex spinal disorder in a patient suffering from acquired TDH in the presence of extensive congenital spine and spinal cord abnormalities. Clinical symptoms and signs can be complemented by neurophysiological techniques to improve diagnostic accuracy and improve the basis for treatment recommendations. In cases involving multiple spinal abnormalities, a comprehensive neurophysiological assessment beyond paravertebral electromyography studies, including nerve conduction and somatosensory-evoked potential recordings, is recommended to assist in confirming the diagnosis.

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, 35–52u2009°C) followed by increased (IB, 42–52u2009°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 N2u2009latencies 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.