Jefferson C. Slimp

Clinical experience with dexmedetomidine for implantation of deep brain stimulators in Parkinson's disease

The pharmacologic profile of the α-2 agonist dexmedetomidine (Dex) suggests that it may be an ideal sedative drug for deep brain stimulator (DBS) implantation. We performed a retrospective chart review of anesthesia records of patients who underwent DBS implantation from 2001 to 2004. In 2003, a clinical protocol with Dex sedation for DBS implantation was initiated. Demographic data, use of antihypertensive medication, and duration of mapping were compared between patients who received Dex (11 patients/13 procedures) and patients who did not receive any sedation (controls: 8 patients/9 procedures). There were no differences in severity of illness between the two groups. Dex provided patient comfort and surgical satisfaction with mapping in all cases, and significantly reduced the use of antihypertensive medication (54% in the Dex group, versus 100% in controls, P = 0.048). In DBS implantation, sedation with Dex did not interfere with electrophysiologic mapping, and provided hemodynamic stability and patient comfort. Routine use of Dex in these procedures may be indicated.

Use of somatosensory-evoked potentials and cognitive event-related potentials in predicting outcomes of patients with severe traumatic brain injury.

Lew HL, Dikmen S, Slimp J, Temkin N, Lee EH, Newell D, Robinson LR: Use of somatosensory-evoked potentials and cognitive event-related potentials in predicting outcomes of patients with severe traumatic brain injury. Am J Phys Med Rehabil 2003;82:53–61. Objective This study was performed to evaluate the usefulness of somatosensory-evoked potentials (SEPs) and cognitive event-related potentials (ERPs) in predicting functional outcomes of severe traumatic brain injury patients. Design Prospective study of 22 patients with severe traumatic brain injury. Demographic information, Glasgow Coma Scale, and electrophysiologic measurements were recorded. Functional outcomes, as quantified by the Glasgow Outcome Scale–Extended, were obtained. Results Bilateral absence of median nerve SEP was strongly predictive of the worst functional outcome. The specificity and positive predictive value of absent SEP for predicting death or persistent vegetative state at 6 mo after traumatic brain injury were as high as 100%. If the definition of unfavorable outcome was expanded to include Glasgow Outcome Scale–Extended 1–4, absence of ERP was equivalent to the absence of SEP in specificity and positive predictive value. On the other hand, normal ERPs showed higher sensitivity and negative predictive value for prognosticating the best outcomes compared with normal SEPs. If the definition of favorable outcome was expanded to include Glasgow Outcome Scale–Extended 5–8, ERP was still superior to SEP for prognosticating good outcome. Interestingly, the highest sensitivity and negative predictive value for favorable outcomes were associated with the presence of any discernible waveform. Conclusions Although median nerve SEP continues to make reliable prediction of ominous outcome in severe traumatic brain injury, the addition of the speech-evoked ERPs may be helpful in predicting favorable outcomes. The strength of the latter test seems to complement the weakness of the former.

Somatosensory evoked potentials after removal of somatosensory cortex in man

Somatosensory evoked potentials (SEPs) to median nerve, ulnar nerve, thumb, middle finger, and posterior tibial nerve stimulation were recorded in a patient with a discrete resection of part of the postcentral somatosensory cortex as a treatment for focal epilepsy. Comparison of the different stimulation sites confirmed electrophysiologically the restricted locus of the lesion. The results strongly suggest that the early negative component (N20) and subsequent components recorded postcentrally are of cortical origin and depend upon postcentral gyrus cytoarchitectonic areas 3, 2, and 1. Moreover, these postcentral SEPs are distinct from precentrally recorded activity.

Dermatomal somatosensory evoked potentials: cervical, thoracic, and lumbosacral levels

Somatosensory evoked potentials were recorded at the scalp to stimulation of the skin at C4, C5, C6, C7, C8, T2, T4, T6, T8, T10, T12, L2, L3, L4, L5, and S1 dermatomes and of the tibial nerve. Stimulation and recording techniques are described. Data were obtained from 41 normal subjects, 25 of which had all 16 dermatomes studied. Wave form descriptions include both typical and atypical presentations. Descriptive statistics for latency, amplitude, left to right comparisons, and level to level comparisons are given. Scalp response latencies for distal extremity dermatomes were well correlated with height but not with vertebral column length, whereas latencies for thoracic dermatomes were not well correlated with either height or vertebral column length. Since scalp response amplitude data were not normally distributed, they were logarithmically transformed and minimum and maximum limits for 1 S.D., 2 S.D., and 3 S.D. derived. Left/right amplitude ratios were similarly treated. Level to level comparisons were achieved with a Z score concordance analysis, which showed that the response values at one level can be used to predict the response values at another level.

What's New in MRI of Peripheral Nerve Entrapment?

New developments in clinical peripheral nerve imaging with MRI over the past few years, primarily those related to nerve entrapment syndromes, are reviewed. The basic principles of peripheral nerve imaging are described briefly. Relevant current or forthcoming technical innovations are described, and then recent work describing novel findings, organized by anatomic location (brachial plexus, upper extremity, and lower extremity), is reviewed. The review concludes with a summary and suggestions of areas in which future clinical research would be particularly helpful.

Staged unilateral versus bilateral subthalamic nucleus stimulator implantation in Parkinson disease.

In 17 consecutive patients with Parkinson disease (PD), bilateral subthalamic nucleus (STN) stimulators were implanted during staged surgeries. The Unified Parkinson Disease Rating Scale (UPDRS) and the Dyskinesia Disability Scale were completed both off and on medication prior to any surgery and also OFF and ON stimulation after each surgery. On‐medication UPDRS activities of daily living (ADL) and motor examination scores changed little with unilateral or bilateral stimulation. Off‐medication UPDRS motor examination scores improved to similar degrees after each staged STN electrode implantation. Most of the improvements in off‐medication ADL scores, dyskinesia scores, complications of therapy, and medication dose reduction occurred after unilateral STN stimulation with smaller improvements after the second operation.

Electrophysiologic intraoperative monitoring for spine procedures.

The advent of equipment capable of performing SEPs, MEPs, and EMG in a multiplexed manner and in a timely fashion brings a new level of monitoring that far exceeds the previous basic monitoring done with SEPs only. Whether this more comprehensive monitoring will result in greater protection of the nervous system awaits future analysis. In any event, monitoring of the spinal cord with SEPs is an accepted standard of care for cases that place the spinal cord at risk. Likewise, nerve root monitoring with EMG is a widely practiced form of monitoring and shows great benefit. MEPs and reflex monitoring, which address the descending pathways and the interneuronal connections, is efficacious in detecting abnormalities that may be missed by SEPs.

Gait changes in response to subthalamic nucleus stimulation in people with Parkinson disease: a case series report.

Background and Purpose For individuals with advanced Parkinson disease (PD), stimulation of the subthalamic nucleus (STN) reduces tremor, rigidity, and bradykinesia, but the effects of stimulation on gait and mobility are not fully understood. The purpose of this paper is to describe the effects of unilateral and bilateral STN stimulation on gait following staged stimulator implantations in a series of individuals with PD. Case Descriptions Participants were 6 individuals with PD who underwent staged stimulator implantation surgeries. The effects of stimulation on gait were assessed in the optimally medicated state using items from the Unified Parkinsons Disease Rating Scale (UPDRS) related to gait and self-reported mobility, time to complete the Timed Up and Go (TUG) test, and quantitative gait analysis. Gait was evaluated with stimulation turned off and with stimulation turned on after unilateral stimulator implantation and again after implantation of the second stimulator. Outcomes Variable effects of unilateral and bilateral STN stimulation on gait were observed on UPDRS self-reported mobility, TUG time, and gait velocity, but changes were not detected using the UPDRS gait item. Minimal gait changes, either positive or negative, were detected with unilateral stimulation. With bilateral stimulation, gait improved for 3 individuals but worsened for the other 3 individuals. Discussion The ability to detect changes in gait after STN stimulation using the UPDRS gait item was limited, but variable effects were detected by self-report, TUG time, and gait velocity. For half of the individuals studied, bilateral stimulation improved these measures, but gait worsened for the remaining individuals. Future research is needed to better understand factors that influence the effect of STN stimulation on walking, and assessment of gait changes in people with PD should include self-report and performance-based measures, such as the TUG test or gait velocity.

Somatosensory evoked potential monitoring during closed humeral nailing: a preliminary report.

OBJECTIVES To assess the role of intraoperative somatosensory evoked potential (SSEP) monitoring of the radial and median nerves in preventing iatrogenic nerve injury during closed, locked intramedullary (IM) nailing of the humerus. DESIGN Prospective clinical study. SETTING Pacific Northwest Level One trauma center and Southern California military medical center. PATIENTS Thirteen patients with indications for surgical stabilization of fractures of the humeral diaphysis and either unknown neurologic status of the affected limb or anticipated difficult reduction maneuvers due to fracture complexity or displacement. INTERVENTION Closed, antegrade or retrograde locked IM nailing of the humerus was attempted while intraoperative monitoring of the radial and median nerves with SSEP was performed. MAIN OUTCOME MEASUREMENTS Intraoperative radial and median nerve SSEP changes during closed fracture manipulation, guide rod insertion, reaming, and humeral nail placement. RESULTS Baseline recordings were obtained in twelve of thirteen patients for both the radial and median nerves. An absence of radial nerve signal in one patient with a closed head injury prompted an open procedure, revealing entrapment of the radial nerve in the fracture. Intraoperative SSEP changes were observed in two of the twelve remaining patients during fracture manipulation and distal interlocking. The signal amplitude returned after discontinuation of manipulation and traction, and alteration of the interlocking maneuver. No neurologic deficits were noted in these two patients. CONCLUSIONS Intraoperative radial nerve SSEP monitoring appears to reliably reflect the status of the radial nerve in those patients with a humerus fracture. In three of eleven patients, intraoperative signal changes prompted a change in surgical plan. In no patient did there appear to be evidence of iatrogenic nerve injury.

Facial nerve mapping and monitoring in lymphatic malformation surgery

OBJECTIVE Establish the efficacy of preoperative facial nerve mapping and continuous intraoperative EMG monitoring in protecting the facial nerve during resection of cervicofacial lymphatic malformations. METHODS Retrospective study in which patients were clinically followed for at least 6 months postoperatively, and long-term outcome was evaluated. Patient demographics, lesion characteristics (i.e., size, stage, location) were recorded. Operative notes revealed surgical techniques, findings, and complications. Preoperative, short-/long-term postoperative facial nerve function was standardized using the House-Brackmann Classification. Mapping was done prior to incision by percutaneously stimulating the facial nerve and its branches and recording the motor responses. Intraoperative monitoring and mapping were accomplished using a four-channel, free-running EMG. Neurophysiologists continuously monitored EMG responses and blindly analyzed intraoperative findings and final EMG interpretations for abnormalities. RESULTS Seven patients collectively underwent 8 lymphatic malformation surgeries. Median age was 30 months (2-105 months). Lymphatic malformation diagnosis was recorded in 6/8 surgeries. Facial nerve function was House-Brackmann grade I in 8/8 cases preoperatively. Facial nerve was abnormally elongated in 1/8 cases. EMG monitoring recorded abnormal activity in 4/8 cases--two suggesting facial nerve irritation, and two with possible facial nerve damage. Transient or long-term facial nerve paresis occurred in 1/8 cases (House-Brackmann grade II). CONCLUSIONS Preoperative facial nerve mapping combined with continuous intraoperative EMG and mapping is a successful method of identifying the facial nerve course and protecting it from injury during resection of cervicofacial lymphatic malformations involving the facial nerve.