Nicolas K. K. King

Estimation of cortical silent period following transcranial magnetic stimulation using a computerised cumulative sum method.

The cortical silent period (CSP) following transcranial magnetic stimulation (TMS) of the motor cortex can be used to measure intra-cortical inhibition and changes in a number of important pathologies affecting the central nervous system. The main drawback of this technique has been the difficulty in accurately identifying the onset and offset of the cortical silent period leading to inter-observer variability. We developed an automated method based on the cumulative sum (Cusum) technique to improve the determination of the duration and area of the cortical silent period. This was compared with experienced raters and two other automated methods. We showed that the automated Cusum method reliably correlated with the experienced raters for both duration and area of CSP. Compared with the automated methods, the Cusum also showed the strongest correlation with the experienced raters. Our results show the Cusum method to be a simple, graphical and powerful method of detecting low-intensity CSP that can be easily automated using standard software.

External Validation of the CRASH and IMPACT Prognostic Models in Severe Traumatic Brain Injury

An accurate prognostic model is extremely important in severe traumatic brain injury (TBI) for both patient management and research. Clinical prediction models must be validated both internally and externally before they are considered widely applicable. Our aim is to independently externally validate two prediction models, one developed by the Corticosteroid Randomization After Significant Head injury (CRASH) trial investigators, and the other from the International Mission for Prognosis and Analysis of Clinical Trials in Traumatic Brain Injury (IMPACT) group. We used a cohort of 300 patients with severe TBI (Glasgow Coma Score [GCS] ≤8) consecutively admitted to the National Neuroscience Institute (NNI), Singapore, between February 2006 and December 2009. The CRASH models (base and CT) predict 14 day mortality and 6 month unfavorable outcome. The IMPACT models (core, extended, and laboratory) estimate 6 month mortality and unfavorable outcome. Validation was based on measures of discrimination and calibration. Discrimination was assessed using the area under the receiving operating characteristic curve (AUC), and calibration was assessed using the Hosmer-Lemeshow (H-L) goodness-of-fit test and Cox calibration regression analysis. In the NNI database, the overall observed 14 day mortality was 47.7%, and the observed 6 month unfavorable outcome was 71.0%. The CRASH base model and all three IMPACT models gave an underestimate of the observed values in our cohort when used to predict outcome. Using the CRASH CT model, the predicted 14 day mortality of 46.6% approximated the observed outcome, whereas the predicted 6 month unfavorable outcome was an overestimate at 74.8%. Overall, both the CRASH and IMPACT models showed good discrimination, with AUCs ranging from 0.80 to 0.89, and good overall calibration. We conclude that both the CRASH and IMPACT models satisfactorily predicted outcome in our patients with severe TBI.

Use of programmable versus nonprogrammable shunts in the management of hydrocephalus secondary to aneurysmal subarachnoid hemorrhage: a retrospective study with cost-benefit analysis

OBJECTIVES The choice of programmable or nonprogrammable shunts for the management of hydrocephalus after aneurysmal subarachnoid hemorrhage (SAH) remains undefined. Variable intracranial pressures make optimal management difficult. Programmable shunts have been shown to reduce problems with drainage, but at 3 times the cost of nonprogrammable shunts. METHODS All patients who underwent insertion of a ventriculoperitoneal shunt for hydrocephalus after aneurysmal SAH between 2006 and 2012 were included. Patients were divided into those in whom nonprogrammable shunts and those in whom programmable shunts were inserted. The rates of shunt revisions, the reasons for adjustments of shunt settings in patients with programmable devices, and the effectiveness of the adjustments were analyzed. A cost-benefit analysis was also conducted to determine if the overall cost for programmable shunts was more than for nonprogrammable shunts. RESULTS Ninety-four patients underwent insertion of shunts for hydrocephalus secondary to SAH. In 37 of these patients, nonprogrammable shunts were inserted, whereas in 57 programmable shunts were inserted. Four (7%) of 57 patients with programmable devices underwent shunt revision, whereas 8 (21.6%) of 37 patients with nonprogrammable shunts underwent shunt revision (p = 0.0413), and 4 of these patients had programmable shunts inserted during shunt revision. In 33 of 57 patients with programmable shunts, adjustments were made. The adjustments were for a trial of functional improvement (n = 21), overdrainage (n = 5), underdrainage (n = 6), or overly sunken skull defect (n = 1). Of these 33 patients, 24 showed neurological improvements (p = 0.012). Cost-benefit analysis showed

Differential effects of endurance and resistance training on central fatigue

646.60 savings (US dollars) per patient if programmable shunts were used, because the cost of shunt revision is a lot higher than the cost of the shunt. CONCLUSIONS The rate of shunt revision is lower in patients with programmable devices, and these are therefore more cost-effective. In addition, the shunt adjustments made for patients with programmable devices also resulted in better neurological outcomes.

Value of routine early post-operative computed tomography in determining short-term functional outcome after drainage of chronic subdural hematoma: An evaluation of residual volume

Abstract The effect of long-term endurance and resistance training on central fatigue has been studied using transcranial magnetic stimulation by exercising the biceps brachii to exhaustion and recording motor-evoked potentials from the non-exercised homologous biceps. Three groups of eight healthy individuals took part: two groups of individuals who had more than 8 years of athletic training in either an endurance or resistance sport, and a group of controls. The size of a motor-evoked potential (area of averaged rectified response) was significantly depressed in all three groups in the non-exercised arm after exhaustive exercise of the opposite arm. Recovery of motor-evoked potentials occurred earlier in endurance athletes (20 min) than in control participants (30 min) and resistance athletes (>30 min). Dexterity and maximum voluntary contraction of the biceps for the non-exercised arm were not depressed in any group. In a separate session, the limit of endurance time for the biceps was reduced significantly following exhaustive exercise of the biceps of the other arm for resistance athletes and control participants, whereas there was no change in the endurance athletes. Our findings suggest that athletic training has an effect on the mechanism of central fatigue that may be specific to the nature of training.

A computed tomography morphometric study of occipital bone and C2 pedicle anatomy for occipital-cervical fusion

Background: Computed tomography (CT) scans are widely used in managing chronic subdural hematoma (CSDH). Factors that determine early post-operative volume have not been examined. The value of routine early post-operative residual volume have not been evaluated. Our study aims to compare pre-operative and early post-operative CT findings to determine the factors affecting residual hematoma and evaluate if early post-operative CT scans are useful in the management of CSDH. Methods: Forty-three patients who underwent burr hole drainage of unilateral CSDH from August 2006 to January 2013 and had routine post-operative CT scans within 48 hours of surgery were selected. Data regarding age, sex, neurological deficit, Glasgow Coma Scale (GCS), pre-existing medical conditions, use of antiplatelets or anticoagulation, operative time, usage of drains, and number of burr holes were obtained. The pre-operative CSDH volume, CSDH density, and midline shift were measured. Residual volume was calculated from early post-operative CT scans. Clinical outcome was evaluated with Glasgow Outcome Scale (GOS) at the time of discharge. Statistical analysis was performed to look for correlation between the pre-operative factors and residual volume, and the residual volume and GOS. Results: Pre-operative volume was found to correlate significantly with post-operative residual volume. There was no significant correlation between all other pre-operative factors and residual volume. There was also no correlation between residual volume and GOS at discharge. Conclusion: Routine post-operative CT brain for burr hole drainage of CSDH may be unnecessary in view of the good predictive value of pre-operative volume, and also because it is not predictive of the clinical outcome.

Effect of prior statin use on outcome after severe traumatic brain injury in a South-East Asian population.

Background: Occipital-cervical fusion (OCF) has been used to treat instability of the occipito-cervical junction and to provide biomechanical stability after decompressive surgery. The specific areas that require detailed morphologic knowledge to prevent technical failures are the thickness of the occipital bone and diameter of the C2 pedicle, as the occipital midline bone and the C2 pedicle have structurally the strongest bone to provide the biomechanical purchase for cranio-cervical instrumentation. The aim of this study was to perform a quantitative morphometric analysis using computed tomography (CT) to determine the variability of the occipital bone thickness and C2 pedicle thickness to optimize screw placement for OCF in a South East Asian population. Methods: Thirty patients undergoing cranio-cervical junction instrumentation during the period 2008-2010 were included. The thickness of the occipital bone and the length and diameter of the C2 pedicle were measured based on CT. Results: The thickest point on the occipital bone was in the midline with a maximum thickness below the external occipital protuberance of 16.2 mm (±3.0 mm), which was thicker than in the Western population. The average C2 pedicle diameter was 5.3 mm (±2.0 mm). This was smaller than Western population pedicle diameters. The average length of the both pedicles to the midpoint of the C2 vertebral body was 23.5 mm (±3.3 mm on the left and ±2.3 mm on the right). Conclusions: The results of this first study in the South East Asian population should help guide and improve the safety in occipito-cervical region instrumentation. Thus reducing the risk of technical failures and neuro-vascular injury.

Serum procalcitonin is a marker for prediction of readmission from an intermediate care to an acute care hospital in neurosurgical patients.

Abstract Introduction: Traumatic brain injury (TBI) is a global concern associated with high mortality and morbidity. Costs to individuals and society are extensive due to poor recovery, long-term disability and the young age group affected. Statins have emerged as potential therapeutic agents in TBI. This study aimed to investigate the protective effect of statins in severe TBI. Methods: This case-control study included adults with severe TBI. A sliding dichotomy approach was used to dichotomize mortality at 14-days and Glasgow Outcome Score (GOS) at 6 months. Logistic regression analysis was used to calculate the odds ratios (OR) for 14-day mortality and 6-month GOS. Results: Equivalent cohorts of 59 age- and sex-matched statin and non-statin users were selected, resulting in population of 118 (mean age = 70.2 years, SD = 10.3), with a median Glasgow Coma Score of 5. Statins did not reduce the likelihood of mortality at 14 days (adjusted OR = 1.23, p = 0.68) or unfavourable outcome at 6 months (adjusted OR = 1.19, p = 0.78). Conclusions: Despite increasing evidence for benefit of statins in TBI, this study in an Asian population does not support this association, demonstrating no significant improvement in outcome for statin users. Further research is required to understand the mechanisms and impact of statins in TBI.

PTMS 1 Pre-and post-surgical assessment of cervical myelopathy: a transcranial magnetic stimulation study

Background: Readmission of patients to acute hospitals contributes significantly toward inefficient utilization of healthcare resources, with studies quoting up to 90% being preventable. We aim to report and analyze the factors involved in the readmission of neurosurgical patients who had been previously transferred to an intermediate step-down care facility, and explore possible predictive markers for such readmissions. Methods: We conducted a retrospective analysis of all 129 neurosurgical patients who were transferred from out acute tertiary hospital to an intermediate care facility. The cases were segregated into those who were readmitted and those who were not readmitted back to our acute center. The demographic data, clinical features, diagnoses, treatment modalities, pretransfer laboratory findings, and inpatient complications were compared with readmission rate. Results: There were 23 patients (17.8%) who were readmitted to our acute hospital. The most common causes of readmission was infection (n = 12, 52.2%). We found a statistically significant correlation between the higher pretransfer procalcitonin levels with the readmission of our patients (P = 0.037). There was also a significant difference noted between ethnic groups (P = 0.026) and having no complications of disease or treatment (P = 0.008), with readmission. Conclusion: Procalcitonin is a pro-hormone known to correlate with infection and poor neurological status. We have found that its serum values correlate significantly with the readmission rates of neurosurgical patients in our study. We postulate that by ensuring normality in procalcitonin levels prior to transfer to an intermediate care facility, potentially half of neurosurgical readmissions can be prevented.

Reliability of cutaneous electrical perceptual threshold in the assessment of sensory perception in patients with spinal cord injury.

cortical stimulation, absence of response on the right side and abnormal response for latency and amplitude on the left side; after lumbar stimulation normal response was elicitated bilaterally. Over time the patient partially recovered her neurological deficit spontaneously and on the ten days a MEP for cortical stimulation was recorded bilaterally, although reduced for amplitude. After four months her recover was complete and the MEP investigations documented a normal cortical response for amplitude and latency on both sides. Discussion: Brain mechanisms underlying conversion symptoms haven’t been elucidated so far. Dysfunction at thalamus level (Sackeim et al 1979) or at prefrontal cortex (Oakley et al, 1999) have been postulated; moreover, a distorsion of sensory or motor representation has been suggested (Brown et al 2004). Our results could reveal an inhibition of motor cortex, maybe through changing in its connectivity with midline brain regions, as documented in functional MRI studies (Cojan Y et al 2009). Conclusions: Unlike commonly reported MEP abnormalities seem to be compatible with conversion disorders and could explain the pathophysiology of these conditions.