Frequent neuromonitoring loss during the completion of vertebral column resections in severe spinal deformity surgery

Background Context

Intraoperative monitoring (IOM) is an essential method for preventing postoperative spinal deficits during posterior vertebral column resection (VCR) surgery for treatment of severe spine deformities, but the IOM features directing at VCR procedures are rarely reported and need to be further clarified.

Neurophysiological evidence of corticospinal tract abnormality in patients with Parkin mutations

Mutations in the parkin gene (PARK2) are the most frequent cause of autosomal recessive early–onset Parkinson disease. We performed a transcranial magnetic stimulation study in four patients with parkin mutations. Two patients had a prolonged central motor conduction time at both upper and lower limb, one only at the arm and one only at the leg. The MEP threshold was increased in one patient for the arm and in two for the leg. The MEP amplitude was reduced in one and central silent period shortened in two. The findings demonstrate corticospinal dysfunction in these patients and suggest that the extent of central nervous system involvement in parkin disease may be wider that hitherto supposed.     

Maternal urinary phthalate metabolites during pregnancy and thyroid hormone concentrations in maternal and cord sera: The HOME Study

Background

Phthalates, endocrine-disrupting chemicals that are commonly found in consumer products, may adversely affect thyroid hormones, but findings from prior epidemiologic studies are inconsistent.

A comparison of the absolute amplitude of motor evoked potentials among groups of patients with various concentrations of nitrous oxide

Purpose It has been shown in previous studies that nitrous oxide (N₂O) suppresses the amplitude of motor evoked potentials (MEPs) in individual subjects. In the present study, we compared the absolute amplitude and latency of MEPs among groups of patients with various concentrations of N₂O.Methods The subjects were 60 patients who were scheduled to undergo craniotomy with MEP monitoring. Anesthesia was induced and maintained with propofol and fentanyl. The patients were randomly assigned to one of three groups based on the concentration of N₂O: 0% N₂O (N0 group), 50% N₂O (N50 group), and 66% N₂O (N66 group). MEPs were elicited by transcranial electrical stimulation. The effect-site concentrations (ESCs) of anesthetics were calculated retrospectively. The effects of anesthetics on MEP were analyzed by analysis of covariance (ANCOVA) followed by Tukeys method.Results MEPs were elicited in all cases. The absolute amplitude of the MEP was significantly higher in the N0 group than in the N50 and N66 groups [4.16 ± 0.42 vs 1.00 ± 0.26mV and 1.00 ± 0.27mV, respectively (mean ± SD); P < 0.05]. In contrast, there was no significant difference in the latency of the MEP among the three groups of subjects (N0: 16.64 ± 0.72, N50: 16.78 ± 0.66, and N66: 16.82 ± 0.63ms).Conclusion The results suggest that N₂O can suppress the absolute amplitude of the MEP in patients under propofol and fentanyl anesthesia. Although monitoring of MEP as a trend is feasible even if N₂O is used, the use of N₂O may be better avoided.This paper was presented in part at the annual meeting of the American Society of Anesthesiologists, Orlando, Florida, USA, on October 12–16, 2002.     

国人大脑皮层与脊髓电刺激多导联描记MEP正常值

报告国人上、下肢共２４块肌于大脑皮层与脊髓电刺激时的运动诱发电位（ＭＥＰ）正常值。无论上肢或下肢，ＭＥＰ潜伏期均因肌肉所在位置而异，越是远端肌潜伏期越长，认为此乃脊神经长度不同所致。但中枢运动传导时间（ＣＭＣＴ）则与脊神经长度、肢长及身高无关，此为锥体束功能的最重要指标。肌肉轻度收缩时，皮层刺激的ＭＥＰ潜伏期缩短，波幅增高，认为系上运动神经元的易化所致。作者认为，ＭＥＰ的多导记录能减少刺激次数，一次性刺激即能同时获得多块肌的ＥＭＰ记录；有利于髓内和神经根病变的定位诊断。     

Sensorimotor integration to cutaneous afferents in humans: the effect of the size of the receptive field

Transcranial magnetic stimulation (TMS) can be used to study sensorimotor integration in humans non-invasively. Motor excitability has been found to be inhibited when afferent stimuli are given to a peripheral nerve and precede TMS at interstimulus intervals (ISIs) of 20–50 ms. This phenomenon has been referred to as short-latency afferent inhibition (SAI). To better understand the functional meaning of these phenomena, we examined the effect of the size of the receptive field on SAI to cutaneous afferents in upper-limb sensorimotor areas in humans. We examined the effect of the stimulation of the isolated right first (D₁), second (D₂) and third finger (D₃), the right second and third finger together (D₂₃) and the right first three fingers together (D₁₂₃) on the amplitude of motor evoked potentials (MEPs) to TMS in hand and forearm muscles. We examined the right abductor pollicis brevis (APB), first dorsal interosseous (FDI), extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles. Digital stimulation preceded TMS at ISIs of 20–50 ms. The effect of D₂ stimulation was MEP inhibition (SAI), which was more marked and consistent in APB and FDI muscles than in ECR and FCR muscles. Similarly, D₁ and D₃ stimulation caused MEP reduction, while no MEP enhancement could be found to single finger stimulation. In contrast, D₁₂₃ stimulation induced less effective SAI in upper-limb muscles. MEP potentiation was recorded in some muscles to D₁₂₃ stimulation. A significant difference between D₂ and D₁₂₃ stimulation was found in APB (ISIs = 30–50 ms) and FDI (ISIs = 40–50 ms) muscles, but not in forearm muscles. The effect to D₂₃stimulation on MEP amplitude was intermediate between those to D₂ and D₁₂₃ stimulation. Our data suggest that motor excitability to cutaneous afferents may be influenced by the size of the receptive fields, this effect being the result of increasing convergence between hand afferents in the somatosensory system. These phenomena appear to be topographically arranged across the representation of upper-limb muscles. These findings may help to understand the functional significance of SAI in normal physiology and pathophysiology.     

Intensity modulation of TMS-induced cortical excitation: primary motor cortex

The intensity dependence of the local and remote effects of transcranial magnetic stimulation (TMS) on human motor cortex was characterized using positron-emission tomography (PET) measurements of regional blood flow (BF) and concurrent electromyographic (EMG) measurements of the motor-evoked potential (MEP). Twelve normal volunteers were studied by applying 3 Hz TMS to the hand region of primary motor cortex (M1(hand)). Three stimulation intensities were used: 75%, 100%, and 125% of the motor threshold (MT). MEP amplitude increased nonlinearly with increasing stimulus intensity. The rate of rise in MEP amplitude was greater above MT than below. The hemodynamic response in M1(hand) was an increase in BF. Hemodynamic variables quantified for M1(hand) included value-normalized counts (VNC), intensity (z-score), and extent (mm(3)). All three hemodynamic response variables increased nonlinearly with stimulus intensity, closely mirroring the MEP intensity-response function. VNC was the hemodynamic response variable which showed the most significant effect of TMS intensity. VNC correlated strongly with MEP amplitude, both within and between subjects. Remote regions showed varying patterns of intensity response, which we interpret as reflecting varying levels of neuronal excitability and/or functional coupling in the conditions studied.