Somatosensory evoked potentials after posterior tibial nerve stimulation--normative data in children

Determination of tibial somatosensory evoked potentials predicts detrusor sphincter dyssynergia in children with neurogenic bladder dysfunction

INTRODUCTION

Tibial somatosensory evoked potentials (SEP) are used to identify the neurological status and tethered cord (TC) in patients with spina bifida (SB). Its significance in contributing to the interpretation of urodynamics to determine bladder status is unknown. This study aimed to determine the correlation between SEP and urodynamics in children with SB.

MATERIAL AND METHODS

SEP and urodynamic results, for differential diagnosis of TC, were evaluated. SEP scores were correlated with urodynamic findings. SEP results were scored from 1 to 6, with 1, denoting a favorable score and 6, an unfavorable score. Age, gender, detrusor, and sphincter activities in urodynamics were noted. Results were analyzed using the χ² test and logistic regression analysis. Receiver operating characteristic (ROC) curve was formed to get a valid threshold for the SEP score to predict the urodynamic condition.

RESULTS

There were 44 SB patients for whom SEP was done for differential diagnosis of TC. Fifteen patients who did not meet the inclusion criteria were excluded from the study. SB aperta was present in 17 patients and occulta in 12, respectively. The patients had a mean age of 6.6 ± 3.2 years. There were 13 boys and 16 girls. A strong correlation was found between high SEP scores and detrusor sphincter dyssynergia (p < 0.001). A SEP score over 3.5 was found to be 93% sensitive and 73% specific to predict this correlation. There was no relationship between detrusor activity and SEP scores (p = 0.18).

DISCUSSION

Tibial SEP is an important noninvasive adjunct tool for the diagnosis of TC in patients with SB. Urodynamic studies are the gold standard in the evaluation of bladder status in neurogenic bladder dysfunction due to SB. Detrusor sphincter dyssynergia may be regarded as a sign of severe spinal cord injury in these patients.

CONCLUSION

Our findings suggest that in children with neurogenic bladder, high SEP scores may predict the presence of detrusor sphincter dyssynergia but not the status of detrusor function while providing pathophysiological evidence for neural injury.

Evaluation of Neurological Examination, SEP Results, MRI Results, and Lesion Levels in Patients Who Had Been Operated for Myelomeningocele

Objective:

Myelomeningocele is the most severe and the most frequent form of spina bifida. Most of the myelomeningocele patients undergo operations in new-born age. In terms of life quality and rehabilitation, follow-up’s of these patients in the growth and development period after the operation is critical. In our study, our aim is to emphasize the correlation of SEP results with MRI results and clinical features of the myelomeningocele patients.

Materials and Methods:

In our study, we included 36 patients who had undergone myelomeningocele operation and have been followed-up in Istanbul Bilim University Florence Nightingale Hospital, Spina Bifida Research and Treatment Centre. Posterior tibial nerve SEP was performed on each patient and neurological examinations were done in the same session. Results were compared with clinical functional lesion levels, levels of fusion defect and ambulation levels. In order to evaluate SEP results, we used age-related reference values from Boor et al.’s study in 2008. Patients were grouped as normal, unilaterally prolonged, bilaterally prolonged, unilaterally lost, and bilaterally lost.

Results:

The correlations of posterior tibial nerve SEP results were significant with ambulation levels (r = 0.428, P < 0.01), clinical functional lesion levels (r = 0.477, P < 0.01) and fusion defect levels (r = −0.528 P < 0.05). The lumbar SEP results were only significantly correlated with functional lesion levels (r = 0.443 P < 0.05).

Conclusions:

Radiological studies are insufficient when evaluating the functionality of the central nervous system. To fully evaluate the functionality and watch the neurological development with accuracy, especially in operated patients, electrophysiological studies should be an indispensable part of myelomeningocele follow-ups.

Evoked Potentials During Peripheral Stimulation Confirm Electrode Location in Thalamic Subnuclei in Children With Secondary Dystonia

Deep brain stimulation is an elective surgical intervention that improves the function and quality of life in children with dystonia and other movement disorders. Both basal ganglia and thalamic nuclei have been found to be relevant targets for treatment of dystonia in children, including the ventral intermediate nucleus of the thalamus, in which stimulation can control dystonic spasms. Electrophysiological confirmation of correct electrode location within the ventralis intermediate nucleus is thus important for the success of the surgical outcome. The present work shows the evoked potentials response during contralateral median-nerve stimulation at the wrist at low frequency (9 Hz) provides physiological evidence of the electrode's localization within the thalamus. We show the correlation between evoked potentials and magnetic resonance imaging (MRI) and computed tomography (CT) in 14 children undergoing implantation of deep brain stimulation electrodes for secondary dystonia. High fidelity and reproducibility of our results provides a new approach to ensure the electrode localization in the thalamic subnuclei.

Application of Machine Learning Using Decision Trees for Prognosis of Deep Brain Stimulation of Globus Pallidus Internus for Children With Dystonia

BACKGROUND

While Deep Brain Stimulation (DBS) of the Globus pallidus internus is a well-established therapy for idiopathic/genetic dystonia, benefits for acquired dystonia are varied, ranging from modest improvement to deterioration. Predictive biomarkers to aid DBS prognosis for children are lacking, especially in acquired dystonias, such as dystonic Cerebral Palsy. We explored the potential role of machine learning techniques to identify parameters that could help predict DBS outcome.

METHODS

We conducted a retrospective study of 244 children attending King's College Hospital between September 2007 and June 2018 for neurophysiological tests as part of their assessment for possible DBS at Evelina London Children's Hospital. For the 133 individuals who underwent DBS and had 1-year outcome data available, we assessed the potential predictive value of six patient parameters: sex, etiology (including cerebral palsy), baseline severity (Burke-Fahn-Marsden Dystonia Rating Scale-motor score), cranial MRI and two neurophysiological tests, Central Motor Conduction Time (CMCT) and Somatosensory Evoked Potential (SEP). We applied machine learning analysis to determine the best combination of these features to aid DBS prognosis. We developed a classification algorithm based on Decision Trees (DTs) with k-fold cross validation for independent testing. We analyzed all possible combinations of the six features and focused on acquired dystonias.

RESULTS

Several trees resulted in better accuracy than the majority class classifier. However, the two features that consistently appeared in top 10 DTs were CMCT and baseline dystonia severity. A decision tree based on CMCT and baseline severity provided a range of sensitivity and specificity, depending on the threshold chosen for baseline dystonia severity. In situations where CMCT was not available, a DT using SEP alone provided better than the majority class classifier accuracy.

CONCLUSION

The results suggest that neurophysiological parameters can help predict DBS outcomes, and DTs provide a data-driven, highly interpretable decision support tool that lends itself to being used in clinical practice to help predict potential benefit of DBS in dystonic children. Our results encourage the introduction of neurophysiological parameters in assessment pathways, and data collection to facilitate multi-center evaluation and validation of these potential predictive markers and of the illustrative decision support tools presented here.

Somatosensory Evoked Potentials and Central Motor Conduction Times in children with dystonia and their correlation with outcomes from Deep Brain Stimulation of the Globus pallidus internus

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A high proportion (47%) of children with dystonia have evidence of abnormal sensory pathway function.

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Central motor conduction times (CMCTs) and somatosensory evoked potentials (SEPs) show a significant relationship with deep brain stimulation (DBS) outcome, independent of aetiology or cranial MRI.

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CMCTs and SEPs can guide patient selection and help counsel families about potential benefit of DBS.

Objectives

To report Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) in children with dystonia and to test the hypothesis that these parameters predict outcome from Deep Brain Stimulation (DBS).

Methods

180 children with dystonia underwent assessment for Globus pallidus internus (GPi) DBS, mean age 10 years (range 2.5–19). CMCT to each limb was calculated using Transcranial Magnetic Stimulation. Median and posterior tibial nerve SEPs were recorded over contralateral and midline centro-parietal scalp. Structural abnormalities were assessed with cranial MRI. One-year outcome from DBS was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m).

Results

Abnormal CMCTs and SEPs were found in 19% and 47% of children respectively and were observed more frequently in secondary than primary dystonia. Of children proceeding to DBS, better outcome was seen in those with normal (n = 78/89) versus abnormal CMCT (n = 11/89) (p = 0.002) and those with normal (n = 35/51) versus abnormal SEPs (n = 16/51) (p = 0.001). These relationships were independent of dystonia aetiology and cranial MRI findings.

Conclusions

CMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia and relate to DBS outcome.

Significance

CMCTs and SEPs can contribute to patient selection and counselling of families about potential benefit from neuromodulation for dystonia.

Subcortical somatosensory evoked potentials after median nerve and posterior tibial nerve stimulation in high cervical cord compression of achondroplasia

Children with achondroplasia may have high cervical myelopathy from stenosis of the cranio-cervical junction resulting in neurological disability and an increased rate of sudden death. To detect myelopathy we recorded somatosensory evoked potentials after median nerve (MN) and posterior tibial nerve (PTN) stimulation in 77 patients with achondroplasia aged 0.3-17.8 years (mean 2.7 years). In addition to the conventional technique of recording the cortical components and the central conduction time (CCT) we employed non-cephalic and mastoid reference electrodes to record the subcortical waveforms N13b and P13 (MN-SEP) as well as P30 (PTN-SEP), respectively, which are generated near the cranio-cervical junction. The findings were related to the MRI results. Thirty-four patients had abnormal MRI findings including spinal cord compression (n=28) and/or myelomalacia (n=24) at or below the cranio-cervical junction. The sensitivity of the MN-SEPs was 0.74 including all abnormal upper cervical cord MRI findings (specificity 0.98), and the sensitivity was 0.79 (specificity 0.92) for cervical cord compression, respectively. The sensitivity of the PTN-SEPs was 0.52 (specificity 0.93) for all abnormal MRI findings and 0.59 (specificity 0.92) for cervical cord compression. The subcortical SEPs N13b and P13 as well as P30 were more sensitive than the conventional recordings. The MN-SEPs, notably the subcortical tracings, are useful for the detection of cervical myelopathy in children with achondroplasia. The PTN-SEPs are less sensitive. However, the tibial nerve SEPs might contribute additional information from the lumbar or thoracic spinal cord, which was, however, not tested in this study.

Subcortical somatosensory evoked potentials after posterior tibial nerve stimulation in children

We report our normative data of somatosensory evoked potentials (SEP) after posterior tibial nerve (PTN) stimulation from a group of 89 children and 18 adults, 0.4-29.2 years of age. We recorded near-field potentials from the peripheral nerve, the cauda equina, the lumbar spinal cord and the somatosensory cortex. Far-field potentials were recorded from the scalp electrodes with a reference at the ipsilateral ear. N8 (peripheral nerve) and P40 (cortex) were present in all children but one. N20 (cauda equina) and N22 (lumbar spinal cord) were recorded in 94 and 106 subjects, respectively. P30 and N33 (both waveforms probably generated in the brainstem) were recorded in 103 and 101 subjects, respectively. Latencies increased with age, while central conduction times including the cortical component, decreased with age (up to about age 10 years). The amplitudes of all components were very variable in each age group. We report our normative data of the interpeak latencies N8-N22 (peripheral conduction time), N22-P30 (spinal conduction time), N22-P40 (central conduction time) and P30-P40 (intracranial conduction time). These interpeak latencies should be useful to assess particular parts of the pathway. The subcortical PTN-SEPs might be of particular interest in young or retarded children and during intraoperative monitoring, when the cortical peaks are influenced by sedation and sleep, or by anesthesia.

Somatosensory processing in healthy newborns

Attempting to understand more about somatosensory processing in newborns, we give an overview of somatosensory potential studies in preterm and term healthy newborns conducted during the past few decades. In addition, we present some of our recent data from somatosensory studies conducted with magnetoencephalography (MEG). The reviewed studies show maturational patterns of cortical responses to median and tibial nerve stimulation within the preterm-term period. In this era, maturation is reflected mainly as shortening of the latencies and increase in the amplitude of especially the early responses. However, the actual somatosensory processing beyond the latency and amplitude analysis has not been the goal in these studies. Although the somatosensory pathways and cortex are mature enough to produce the evoked responses, difficulties in measuring the neonatal responses with similar parameters as used for adults is suggested to reflect the special characteristics of newborn processing. Possible factors behind the inconsistencies between different newborn studies are discussed.

Maturation of near-field and far-field somatosensory evoked potentials after median nerve stimulation in children under 4 years of age

OBJECTIVES

The maturation of subcortical SEPs in young children.

METHODS

Median nerve SEPs were recorded during sleep in 42 subjects aged 0-48 months. Active electrodes were at the ipsilateral Erb's point, the lower and upper dorsal neck, and the frontal and contralateral centroparietal scalp; reference electrodes were at the contralateral Erb's point, the ipsilateral earlobe and the frontal scalp; bandpass was 10-3000 Hz. The peaks were labelled by their latencies in adults.

RESULTS

The peak latencies of N9 (brachial plexus potential) decreased exponentially with age during the first year, but increased with height thereafter. The interpeak latencies (IPLs) N9-N11, which measure conduction between brachial plexus and dorsal column, decreased with age (linear regression). The IPLs N11-P13 and N11-N13b, which measure conduction between the dorsal column and approximately the cervico-medullary junction, did not change across this age range. The IPLs N13a-N20, N13b-N20 and P13-N20, which measure central conduction, showed negative exponential regressions with rapidly decreasing latencies during the first year of life and slowly decreasing latencies thereafter.

CONCLUSIONS

Maturation of the peripheral segments of the somatosensory pathway progresses more rapidly than that of the central segments. The maturation of central conduction is not completed within the first 4 years of age. Our maturational data may serve as a reference source for subsequent developmental and clinical studies.