Posterior Tibial Somatosensory Evoked Potentials Research Articles

Intraoperative thalamocortical tract monitoring via direct cortical recordings during craniotomy

ObjectiveNeuromonitoring of primary motor regions allows preservation of motor strength and is frequently employed during cranial procedures. Less is known about protection of sensory function and ability to modulate movements, both of which rely on integrity of thalamocortical afferents (TCA) to fronto-parietal regions. We describe our experience with TCA monitoring and their cortical relays during brain tumor surgery. MethodologyTo study its feasibility and usefulness, continuous somatosensory evoked potentials (SSEP) recording via a subdural electrode was attempted in 32 consecutive patients. ResultsMedian and posterior tibial SSEP were successfully monitored in 31 and 17 patients respectively. SSEP improved lesion localization and prevented unnecessary cortical stimulation in 9 and 16 cases respectively. A threshold of ≥30% SSEP amplitude decrease influenced management in 10 patients while a decrement of ≥50 % had a sensitivity of 0.89 and specificity of 1 in detecting worsening of sensory function. Simultaneous motor evoked potentials (MEP) and SSEP monitoring were performed in 10 cases, 9 of which showed short-lived fluctuations of the former. ConclusionDirect cortical SSEP monitoring is feasible, informs management and predicts outcome. SignificanceEarly intervention prevents sensory deficit. Concomitant MEP fluctuations may reflect modulation of motor activity by TCA.

Phase Reversal of Somatosensory Evoked Potentials Triggered by Gracilis Tract Stimulation: Case Report of a New Technique for Neurophysiologic Dorsal Column Mapping

: Reliable visual identification of the median raphae, essential for the preservation of function of the posterior dorsal columns during intramedullary spinal cord tumor resection, is not possible in many cases, because of distorted local anatomy. In such cases, intraoperative neurophysiologic mapping of the dorsal columns offers invaluable information to the surgeon, and guides the myelotomy. We hereby describe such a new technique. : A 41-year-old man with a C3-C4 intramedullary spinal cord tumor underwent successful myelotomy and tumor resection. Dorsal column mapping was performed by use of an 8-contact minielectrode strip placed on the dorsal spinal cord. Direct electrical stimulation was applied via 2 adjacent contacts of the strip at a time, in an attempt to stimulate in succession the left and right dorsal columns. Somatosensory evoked potentials (SSEPs) were recorded after each stimulation, via scalp electrodes. A sharp change in polarity of the recorded scalp SSEPs (phase reversal) indicated when the stimulation of the opposite dorsal column occurred. Myelotomy was performed in between the minielectrode contacts identified as being situated closest to the raphe. The posterior tibial SSEPs were continuously monitored during and after myelotomy and until the dura closure. No changes from premyelotomy SSEPs were present. Postoperatively, the patient had preservation of the posterior column function. : SSEP phase-reversal technique is a promising new method to identify the neurophysiologic midline in intramedullary tumor resection. Fast and easy to perform, its final role in neurophysiologic dorsal column mapping awaits confirmation in future applications.

The Characteristics of Gait Disturbance and Its Relationship with Posterior Tibial Somatosensory Evoked Potentials in Patients with Cervical Myelopathy

Prospective case control study. This study is to investigate the gait characteristics of cervical myelopathy (CM) and to assess the relationship between presence of abnormality of posterior tibial somatosensory evoked potential (PTSEPs) and gait parameters. Many of CM patients suffer from gait disturbance so that the assessment of walking ability and its restoration are one of main concerns. The patients were recruited who had suffered from gait disturbance and were diagnosed as CM by cervical magnetic resonance image (MRI). All subjects underwent three-dimensional gait analysis and PTSEP. Normal persons were recruited as control groups and underwent gait analysis. The CM patients were divided into two groups such as normal and abnormal SEP groups, and two groups were compared as to presence of signal change in MRI and gait parameters. CM groups revealed significantly lower gait velocity, decreased step length and stride length, and increased double support time. They showed significantly decreased maximal knee flexion angle in swing phase, the decreased plantarflexion angle at push off, and the increased maximal dorsiflexion angle at swing phase in comparison with control group. Abnormal SEP group demonstrated the lower gait velocity and cadence, smaller plantarflexion angle at push off and the larger maximal dorsiflexion angle at swing phase in comparison with normal SEP group. There was no significant relationship between presence of SEP abnormality and signal change of MRI. CM patients compensated stabilizing balance by decreasing gait velocity and step length as well as increasing step width and double support time. Considering the presence of abnormality of PTSEP was closely related to typical gait characteristics of CM patient, the gait deviation of CM patients was attributed to impaired proprioception of lower limbs and poor stability.

Serum vitamin B12, folate, and homocysteine levels and their association with clinical and electrophysiological parameters in multiple sclerosis

Patients with multiple sclerosis (MS) may have low serum vitamin B12 and folate levels and high levels of homocysteine. We aimed to evaluate serum vitamin B12, folate, homocysteine, mean corpuscular volume (MCV), hemoglobin (Hb), and hematocrit (Hct) levels in patients with MS. We examined the relationship between these parameters and age, sex, disease type, age at onset, disease duration, Expanded Disability Status Score, immunoglobulin G (IgG) index, oligoclonal band presence, visual evoked potentials (VEP) and posterior tibial somatosensory evoked potentials (SEP). These parameters were evaluated in 35 patients during an acute attack and compared to data collected from 30 healthy individuals (control subjects). Serum vitamin B12, folate, homocysteine, Hb, and Hct levels and MCV were low in a proportion of patients with MS (20%, 14.3%, 20%, 6.7%, 3.3% and 10% respectively), whereas only vitamin B12 and folate levels were low in only 3.3% of the control subjects. Homocysteine levels were high in 20% of patients with MS but were within normal limits in the control group. Elevated Hct levels were significantly correlated ( p < 0.05) with prolonged posterior tibial SEP P1 and P2 latencies compared to the control subjects. Patients with MS who had prolonged VEP and posterior tibial SEP P1 and P2 latencies also had lower vitamin B12 levels compared to patients with normal latencies. Thus, we found a significant relationship between MS and vitamin B12 deficiency, and also demonstrated a relationship between vitamin B12 deficiency, VEP and posterior tibial SEP in MS.

Hirayama disease: three cases assessed by F wave, somatosensory and motor evoked potentials and magnetic resonance imaging not supporting flexion myelopathy

Traumatic chronic injury of the cervical spinal cord caused by neck flexion ("flexion myelopathy") is one of the suggested pathogenetic mechanisms for Hirayama disease (HD). Neurophysiological data, especially reporting particularly N13 cervical somatosensory response, are scarce and conflicting in HD. F wave, somatosensory evoked potentials (SEP), motor evoked potentials (MEP) and magnetic resonance imaging (MRI) studies were assessed in 3 HD male patients (aged 22, 36, and 51 years) with the aim of evaluating the functional effects of neck flexion in HD. Median and ulnar F waves, median, ulnar and posterior tibial SEP, and upper and lower limb MEP were performed bilaterally in standard conditions and during neck flexion in the patients. Cervical spinal MRI study was performed in standard position in two patients and both in standard and flexed positions in the third patient. F wave, SEP, and MEP findings did not show statistically significant differences in standard conditions and during neck flexion both in HD patients and controls. MRI with neck in standard position was normal in two patients, while in the third patient revealed cervical anterior horns signal changes and cord atrophy. In this patient, MRI with the neck in flexion showed that the spinal cord was normally located, was not compressed within the cervical canal and that there were no abnormalities of the dural sac. These findings suggest that in a complex disorder like HD no definite conclusions can be drawn from the present paper and some cases of HD without evidence of "flexion myelopathy" might have a different pathogenetic mechanism.

The role of cortical evoked responses in predicting neuromotor outcome in very preterm infants.

To explore the role of posterior tibial somatosensory evoked potentials (SSEP) and flash visual evoked potentials (VEP) in the early prediction of functional brain injury, 93 infants of less than 32 weeks gestation at birth were studied. Neuromotor outcome was defined by clinical examination at the age of 2 years. SSEP, VEP and cerebral ultrasound were compared as predictors of neuromotor outcome. Posterior tibial SSEP were the most accurate single method of predicting neuromotor abnormalities with a 83% positive predictive power for cerebral palsy and a 100% predictive power for abnormal neurology, compared to 17% and 40% for cerebral ultrasound and 38% and 85% for VEP respectively. When SSEP and VEP results were concordant, the positive predictive power for cerebral palsy and abnormal neurology was 100%. Our results suggest that posterior tibial SSEP and VEP are accurate tools in the prediction of outcome in very preterm infants.

Comparison of Median and Posterior Tibial Nerve Somatosensory Evoked Potentials in Ambulatory Patients with Definite Multiple Sclerosis

Somatosensory evoked potentials (SEPs) were recorded for stimulation of both median nerves and both posterior tibial nerves in control subjects and in subjects with multiple sclerosis (MS) of several years' duration, who were ambulatory and not experiencing exacerbation. Documentation of peripheral nerve conduction revealed no abnormalities in any of the subjects. Centrally, abnormal responses to median and posterior tibial nerve stimulation were found at the spinal level and/or the scalp in nearly all MS patients. Using the latency of the initial negativity of scalp SEPs, posterior tibial SEPs were abnormal significantly more often than median SEPs. Calculations suggested a significant increase in spinal conduction time. The high incidence of abnormal SEPs does not support any substantial physiological recovery in this group of MS patients.

Somatosensory evoked potentials and magnetic resonance imaging in syringomyelia

Somatosensory evoked potentials (SEPs) to median and posterior tibial stimulation were obtained in 22 patients with syringomyelia. All patients had magnetic resonance imaging (MR) which defined the maximum transverse diameter of the syrinx as well as its longitudinal extension. SEP was abnormal in 16 (72%) patients. Median and posterior tibial SEPs were abnormal in 11 and 15 patients respectively. Both tests were abnormal in 10 patients. Ten patients showed absence of one or more central potentials (P/N13, N20, N22) and 7 patients demonstrated increased conduction times (N9–N20, P/N13–N20, N22–P40). The mean maximum transverse diameter of the syrinx was 7.5 mm in patients with normal SEPs and 16.2 mm in patients with abnormal SEPs. Abnormal SEP was observed in all 5 patients with loss of position sense, in 9 of 13 (69%) with loss of superficial pain and temperature, and 1 of 2 patients with motor deficit only. Central SEP abnormalities were observed in 3 of 5 patients with sensory deficits indistinguishable from a peripheral neuropathy and in 2 patients in the asymptomatic extremity. Three of 4 patients with syringomyelia and Chiari malformation had a normal SEP.