Aleksandar Beric

Background/Aim. Neuroplasticity of the somatosensory system can be manifested after short-term or long-term peripheral tactile stimulation. Focused attention has been well established as a modulator of neural processing in the visual and auditory systems. However, its role in the primary somatosensory cortex is insufficiently elucidated. The aim of this study was to examine the effect of focused attention on short-term somatosensory neuroplasticity following repeated tactile stimulation of different intensity over identical locations on the hands and shoulders. The aim of the study was also to determine whether repeated tactile stimulation of different intensity in the shoulder area of the non-dominant hand leads to a reduction in the stimulus thresh-old and to assess whether similar changes occur in the contralateral, unstimulated shoulder somatotopically identical location. Methods. This study included 30 healthy volunteers of both sexes. The contingent negative variation (CNV) wave and the Go/NoGo paradigm for measuring reaction time were used to objectively register the stimulus threshold for light touch, before and after sensory stimulation. The CNV wave was registered within the paradigm with two known stimuli, the first of which was tactile and the second visual in the form of a green or red circle that appeared randomly on the screen. Peripheral sensory stimulation was conducted only over the non-dominant hand and shoulder using multiple series with 12 tactile stimuli of varying intensities. Results. The results showed statistically significant decrease in the stimulus threshold for light touch on both shoulders after tactile stimulation performed only on the non-dominant shoulder. In addition, whenever CNV waves were detected within the Go/NoGo paradigm, reaction times of the subjects were significantly shorter, which served as an objective validation of the initial detection of tactile thresholds before and after peripheral sensory stimulation. Conclusion. Short-term, unilateral tactile stimulation leads to bilateral, functional adaptation of the proximal regions of the upper extremities, which suggests interhemispheric homologous transfer within the somatosensory system, supporting the principle of somatotopic organization in somatosensory neuroplasticity.

Study Design: This is a retrospective analysis of electromyographic (EMG) stimulation thresholds of 64 cortical bone trajectory (CBT) screws. Objective: The authors seek to determine whether recordings below stimulation threshold correlate with CBT screw pedicle breach on computed tomographic imaging, and to explore which specific nerve roots are most at risk with this new trajectory. Summary of Background Data: Intraoperative EMG monitoring has been utilized to verify accurate placement of pedicle screws. Although CBT screws are becoming increasingly popular, to the authors’ knowledge there are no existing evaluations of the accuracy of intraoperative triggered EMG (tEMG) monitoring in this trajectory. Materials and Methods: Retrospective analysis of EMG stimulation thresholds of 64 CBT screws placed in patients at NYU Langone Medical Center from 2015–2017. EMG results including threshold values and muscle group stimulated were correlated with screw positioning determined on postoperative or intraoperative computed tomographic imaging. Results: In total, 4.7% of EMG threshold values indicated true breach, 1.6% were falsely positive for breach, 76.5% showed true absence of breach, 17.1% failed to reveal a present breach though 0% of medial breaches were undetected. L4 screws showed tEMG responses from adductor longus in 22%, L5 screws, from rectus femoris in 16.7%, and S1 screws from tibialis anterior in 50%. Conclusions: tEMG testing is effective for medial breaches in CBT screws. In addition, there is evidence that bicortical placement of these screws causes lower stimulation values due to distal breach. Importantly, it seems that this is due in part to stimulation of the exiting nerve root at the level above.

Intraoperative monitoring is performed to provide real time assessment of the neural structures that can be at risk during spinal surgery. Somatosensory evoked potentials (SEPs) are the most commonly used modality for intraoperative monitoring. SEP stability can be affected by many factors during the surgery. This study is a prospective review of SEP recordings obtained during intraoperative monitoring of instrumented spinal surgeries that were performed for chronic underlying neurologic and neuromuscular conditions, such as scoliosis, myelopathy and spinal stenosis. We analyzed multiple montages at the baseline, and then followed their development throughout the procedure. Our intention was to examine the stability of the SEP recordings throughout the surgical procedure on multiple montages of cortical SEP recordings, with the goal of identifying the appropriate combination of the least number of montages that gives the highest yield of monitorable surgeries. Our study shows that it is necessary to have multiple montages for SEP recordings, as it reduces the number of non-monitorable cases, improves IOM reliability, and therefore could reduce false positives warnings to the surgeons. Out of all the typical montages available for use, our study has shown that the recording montage Cz-C4/Cz-C3 (Cz-Cc) is the most reliable and stable throughout the procedure and should be the preferred montage followed throughout the surgery.

Comparison of T1-T4 decrement between upper and lower extremity muscles can indicate differences between recovery time from neuromuscular blockade, which may have repercussions for neurophysiologic intraoperative monitoring. We investigated decrement between T1 and T4 hand and foot muscle responses on quantitative train-of-four (TOF) test. Study analyzed differences between recovery of foot, abductor hallucis muscle, and hand, first dorsal interosseous muscle, by application of quantitative TOF test on 147 patients undergoing lumbar spine surgery. T1 to T4 decrements on hand and foot TOF were obtained and classified into different groups, depending on elapsed time after administration of neuromuscular blocking agents and its dose. There are significant differences between T1-T4 decrements obtained on hand and foot (P < 0.05). T1-T4 decrement determined on abductor hallucis muscle was lower indicating more rapid recovery than the first dorsal interosseous muscle (P < 0.05). Interestingly, quite opposite, more pronounced decrement in foot TOF than hand was showed in 4% (5 out of all 147 cases). The observed difference between recovery of hand and foot muscles suggests that quantitative TOF test should be performed on extremities for which accurate data about the level of neuromuscular blockade is sought. During lumbar spine surgery monitoring, in addition to hand TOF, foot TOF should be included.

The potential synergy of modulating platinum-induced DNA damage by combining the proteasome inhibitor bortezomib with oxaliplatin was studied in patients with solid tumors, with special attention to avoidance of cumulative neurotoxicity (NT). In a 3 + 3 dose escalation design, patients received bortezomib at 1.0–1.5 mg/m² on days 1 and 4 and oxaliplatin at 60–85 mg/m² on day 1 of a 14-day cycle. NT assessments were performed at the start of every two cycles. Oxaliplatin pharmacokinetics (PK) were determined pre- and post-bortezomib. Thirty patients were enrolled with 25 (11 men, 14 women) fully evaluable for NT assessments at cycle 2. The median age was 56 years (range 35–74 years); median number of cycles received 2 (range 1–10). At dose levels 2–5 (B 1.3 mg/m²), patients manifested NT grades 3 and 4 at a median 3.4 cycles (range 2–9 cycles): 3 had ataxia (one also with sensory neuropathy or neurogenic hypotension, respectively) and 3 had just sensory neuropathy. A 6th dose-level reducing bortezomib to 1.0 mg/m² with oxaliplatin 85 mg/m²) was explored and no NT or dose limiting toxicities were noted among 7 evaluable patients (5 receiving two or more cycles). Four patients experienced a partial response—one with platinum-resistant ovarian cancer, another with gastroesophageal cancer, another with ampulla of Vater carcinoma, and a patient with cholangiocarcinoma. PK studies at dose levels 1 and 2 showed greater mean ultrafiltrable platinum when oxaliplatin was dosed after bortezomib. Bortezomib 1.0 mg/m² × 2 every 14 days combines safely with oxaliplatin. At higher doses, cumulative NT (i.e., cerebellar signs and sensory neuropathy) occurs at an accelerated pace perhaps from a PK interaction.

Objective To determine whether transcranial motor-evoked potential (TCMEP) monitoring of the facial nerve (FN) during cerebellopontine angle (CPA) tumor resection can predict both immediate and long-term postoperative FN function. Design Retrospective review. Setting Tertiary referral center. Main Outcome Measures DeltaTCMEP (final-initial) and immediate and long-term facial nerve function using House Brackmann (HB) rating scale. Results Intraoperative TCMEP data and immediate and follow-up FN outcome are reported for 52 patients undergoing CPA tumor resection. Patients with unsatisfactory facial outcome (HB >2) at follow-up had an average deltaTCMEP of 57 V, whereas those with HB I or II had a mean deltaTCMEP of 0.04 V (t = -2.6, p < 0.05.) Intraoperative deltaTCMEP did not differ significantly between groups with satisfactory (HB I, II) and unsatisfactory (HB > 2) facial function in the immediate postoperative period. Conclusion Intraoperative TCMEP of the facial nerve can be a valuable adjunct to conventional facial nerve electromyography during resection of tumors at the CPA. Intraoperative deltaTCMEP >57 V may be worrisome for long-term recovery of satisfactory facial nerve function.

Retrospective review. The purpose of this study was to assess the preoperative neurologic risk in a consecutive series of spinal deformity patients undergoing correction surgery at one institution. During spinal deformity correction surgery, neurologic monitoring techniques are commonly applied to reduce the risk of neurologic deficits. While previous studies have demonstrated risk factors for neurologic changes in the setting of spinal surgery, these involved long time spans and heterogeneous patient populations. Of 301 cases performed over 1 year, 281 cases were monitorable. Patients were grouped according to diagnosis: neuromuscular (NM) scoliosis, Sagittal Plane deformity, and Scoliosis. Demographic and surgical data were collected for neurologically monitorable patients. Coronal and sagittal parameters were measured using digital images of radiographs. Neurologic status was measured with somatosensory-evoked potentials and/or motor-evoked potentials. Primary NM scoliosis cases had the highest incidence of neurologic monitoring changes (NMC) (10%) while revision sagittal plane deformity had the second highest (9.8%). Sensitivity and specificity were both 100%. Overall incidence of neurologic deficit was 1.1%. Of the 13 NMCs patients, 3 patients had persistent neurologic deficit. Majority of NMCs occurred before deformity correction. In patients with NM scoliosis, NMCs increased with hybrid constructs with wires (P < 0.01). In patients with scoliosis, NMCs increased with increased body mass index, estimated blood loss, operative time, and postoperative coronal thoracolumbar curve magnitude (P < 0.04). In patients with primarily sagittal plane deformity, NMCs increased with preoperative proximal curve, postoperative proximal and thoracolumbar curves, and postoperative kyphosis and lordosis (P < 0.04). Primary NM scoliosis and revision sagittal plane deformities appear to carry greatest incidence of NMCs during surgical intervention. Most observed NMCs did not result in a permanent neurologic deficit. Neuromonitoring should be assessed throughout the entire surgical procedure. This study may aid surgeons and patients to better assess neurologic risks related to spinal deformity surgery.

Overactivity of subthalamic nucleus (STN) neurons is a consistent feature of Parkinson's disease (PD) and is a target of therapy for this disorder. However, the relationship of STN firing rate to regional brain function is not known. We scanned 17 PD patients with ¹⁸F-fluorodeoxyglucose (FDG) PET to measure resting glucose metabolism before the implantation of STN deep brain stimulation electrodes. Spontaneous STN firing rates were recorded during surgery and correlated with preoperative regional glucose metabolism on a voxel-by-voxel basis. We also examined the relationship between firing rate and the activity of metabolic brain networks associated with the motor and cognitive manifestations of the disease. Mean firing rates were 47.2 ± 6.1 and 48.7 ± 8.5 Hz for the left and right hemispheres, respectively. These measures correlated (P< 0.007) with glucose metabolism in the putamen and globus pallidus, which receive projections from this structure. Significant correlations (P< 0.0005) were also evident in the primary motor (BA4) and dorsolateral prefrontal (BA46/10) cortical areas. The activity of both the motor (P< 0.0001) and the cognitive (P< 0.006) PD-related metabolic networks was elevated in these patients. STN firing rates correlated with the activity of the former (P< 0.007) but not the latter network (P = 0.39). The findings suggest that the functional pathways associated with motor disability in PD are linked to the STN firing rate. These pathways are likely to mediate the clinical benefit that is seen following targeted STN interventions for this disease.