Faculty Bibliography

OBJECTIVE: To evaluate the safety, efficacy, and utility of a novel surgical strategy consisting of multiple (more than two) operative stages performed during the same hospital admission with subdural grid and strip electrodes in selected pediatric extratemporal epilepsy. METHODS: Subdural grid and strip electrodes were used for multistage chronic electroencephalographic monitoring in 15 pediatric patients (age, <19 yr) with refractory localization-related epilepsy and poor surgical prognostic factors. Initial resective surgery and/or multiple subpial transections were performed, followed by further monitoring and additional resection and/or multiple subpial transections. RESULTS: Mean patient age was 9.7 years. Mean duration of total invasive monitoring was 10.5 days (range, 8-14 d). The first monitoring period averaged 6.5 days, and the second averaged 3.9 days. Additional surgery was performed in 13 of 15 patients. Two patients who did not undergo additional surgery had a Class I outcome. Rationales for reinvestigation included incomplete localization, multifocality, and proximity to eloquent cortex. Complications were minimal, including two transfusions. There were no cases of wound infection, cerebral edema, hemorrhage, or major permanent neurological deficit. Minimum duration of follow-up was 31 months. Outcomes were 60% Engel Class I (9 of 15 patients), 27% Class III (4 of 15 patients), and 13% Class IV (2 of 15 patients). CONCLUSION: In a very select group of pediatric patients with poor surgical prognostic factors, the multistage approach can be beneficial. After failed epilepsy surgery, subsequent reoperation with additional intracranial investigation traditionally is used when a single residual focus is suspected. Our results, however, support the contention that multistage epilepsy surgery is safe, effective, and useful in a challenging and select pediatric population with extratemporal medically refractory epilepsy

PURPOSE: Cortical tubers are epileptogenic lesions in patients with tuberous sclerosis complex (TSC). Giant cells and dysplastic neurons are pathological hallmarks of cortical tubers. Severe astrogliosis, which is invariably present in tubers, has attracted much less attention. We hypothesize that the development of astrogliosis in cortical tubers constitutes a primary pathology of astrocytes and is directly related to TSC 1/2 mutations. METHODS: To begin to test this hypothesis, we performed immunohistochemical and electron microscopic analysis of brain tuber tissue resected from epileptic TSC patients. We compared alterations in tuber astrocytes to those found in other acute and chronic human epilepsy pathologies. RESULTS: We found that astrogliosis in tubers is comprised of a mixture of 'gliotic' and 'reactive' astrocytes. The majority of tuber astrocytes are 'gliotic' astrocytes that are morphologically and immunophenotypically similar to astrocytes in areas of gliosis in hippocampal sclerosis (HS). However, specific immunostaining features differentiate TSC gliosis from HS gliosis. 'Reactive' tuber astrocytes are large-sized, vimentin positive cells in the vicinity of giant cells that show activation of the mammalian target of rapamycin (mTOR) pathway, consistent with mutated TSC gene function. These cells resemble acutely reactive human astrocytes seen in tissue resected from depth electrode implantation patients. Oligodendrocytes and NG2 expressing glial cells do not have any detectable alterations within tubers. CONCLUSION: We conclude that astrocytes are the type of glial cell selectively impacted in cortical tuber pathology. We propose that tubers may be dynamic lesions, with progression of astrocytes over time from 'reactive' to 'gliotic.' Tuber astrogliosis in TSC may represent a genetic 'model' of gliosis that is phenotypically similar to gliosis seen in acquired human pathologies

The expanded disability status scale (EDSS) is an ordinal score that measures progression in multiple sclerosis (MS). Progression is defined as reaching EDSS of a certain level (absolute progression) or increasing of one point of EDSS (relative progression). Survival methods for time to progression are not adequate for such data since they do not exploit the EDSS level at the end of follow-up. Instead, we suggest a Markov transitional model applicable for repeated categorical or ordinal data. This approach enables derivation of covariate-specific survival curves, obtained after estimation of the regression coefficients and manipulations of the resulting transition matrix. Large sample theory and resampling methods are employed to derive pointwise confidence intervals, which perform well in simulation. Methods for generating survival curves for time to EDSS of a certain level, time to increase of EDSS of at least one point, and time to two consecutive visits with EDSS greater than three are described explicitly. The regression models described are easily implemented using standard software packages. Survival curves are obtained from the regression results using packages that support simple matrix calculation. We present and demonstrate our method on data collected at the Partners MS center in Boston, MA. We apply our approach to progression defined by time to two consecutive visits with EDSS greater than three, and calculate crude (without covariates) and covariate-specific curves.

OBJECTIVE: Cortical tubers are a pathognomonic finding in some patients with tuberous sclerosis complex (TSC), and are believed to be epileptogenic foci. Surgery is an effective option in selected patients with TSC who are refractory to medical therapy. This article describes three patients with TSC who underwent three-stage epilepsy surgery at our center, with the intention of examining local electrophysiological changes after each stage of the procedure. METHODS: Magnetic resonance images were obtained after initial implantation of electrodes and after resection and electrode reimplantation. These images were co-registered and overlaid. The intracranial grids were overlaid in a similar procedure and manually traced, and then added to the volumetric image. Mean spike counts were obtained for each patient and expressed in spikes per minute. Statistical analysis was performed on spike counts prior to and after resection. RESULTS: All three patients displayed intense spiking in the regions around the dominant epileptogenic tuber. On tuber removal, spike counts diminished significantly. In each case, new areas of spiking emerged in regions remote from the tuber periphery after tuber resection, with the emergence of secondary ictal onset zones in the resection margin. CONCLUSION: This retrospective study highlights some common electrophysiological features among the patients examined. The observed epileptogenic activity and regions of ictal onset suggest that it may be the region of brain tissue surrounding the tuber that is responsible for the majority of epileptogenic activity in these patients

Multicenter, retrospective analysis of 70 subjects with TSC following surgery for relief of epilepsy revealed significant associations between younger age at seizure onset, present/prior history of infantile spasms, interictal focality (bilateral versus unilateral), and absence of residual postoperative predominant tuber, and poorer postoperative outcome (p < 0.01). Ictal multifocality, mental retardation, and discordant EEG and MRI data showed a negative trend toward outcome, but were not significant

OBJECTIVE: Transient paraplegia in the immediate postoperative period after lipomyelomeningocele repair is uncommon and is not discussed in the literature. We present the unique case of a patient who developed transient paraplegia 48 hours after lipomyelomeningocele repair attributable to the acute development of a thoracic syrinx. CLINICAL PRESENTATION: At birth, the patient was noted to have a large skin-covered mass in the lumbosacral region. On neurological examination, both iliopsoas and quadriceps exhibited 3/5 motor function, and the plantar flexors and dorsiflexors exhibited 1/5 motor function. Urodynamic studies were normal. Magnetic resonance imaging demonstrated the presence of a lipomyelomeningocele associated with tethering of the spinal cord in the lumbosacral region. INTERVENTION: At 5 months of age, the patient underwent repair of the lipomyelomeningocele. After surgery, the patient developed progressive paraplegia along with bowel and bladder dysfunction. Given the concern about a postoperative hematoma resulting in cauda equina syndrome, the patient returned to the operating room for a wound exploration. No compressive lesion such as a hematoma was found at surgery. A postoperative magnetic resonance imaging scan obtained afterward, however, demonstrated the presence of a large thoracic syrinx. CONCLUSION: Syrinx formation can occur as early as 48 hours after lipomyelomeningocele repair, leading to progressive lower extremity weakness and bowel and bladder incontinence. In the immediate postoperative period, an acute syrinx can mimic cauda equina syndrome, and a magnetic resonance imaging scan is necessary to distinguish between these two entities. In this patient, the syrinx was transient and resolved without a shunting procedure

OBJECTIVE:To develop covariate specific short-term disability curves to demonstrate the probability of progressing by Expanded Disability Status Scale (EDSS) at semiannual visits. METHODS:Semiannual EDSS scores were prospectively collected in 218 relapsing-remitting (RR) and clinically isolated syndrome (CIS) patients as part of the Comprehensive Longitudinal Investigation of Multiple Sclerosis at the Brigham and Women's Hospital (CLIMB) study. Baseline brain parenchymal fraction (BPF) and T2 lesion volume were available on 205 patients. A partial proportional odds model determined the influence of covariates on the change in EDSS score at subsequent visits. A discrete second order Markov transitional model was fit and generated a probability matrix for each subject; the 6-month probabilities of EDSS change were graphically represented. RESULTS:The univariate analysis demonstrated the lowest baseline BPF quartile (OR 1.99; p = 0.0203) and the highest T2 lesion volume quartile (OR 2.19; p = 0.0130) were associated with progression in EDSS. Covariate specific disability curves demonstrated the effect of BPF and T2 lesion volume on short-term progression. In subjects with a 6-month EDSS of 2, the probability of a sustained progression of an EDSS of 3 within 3 years was 0.277 for a subject with low BPF and a high T2 lesion volume vs 0.055 for a subject with high BPF and a low T2 lesion volume. CONCLUSIONS:Markov transitional models allow for the comparison of covariate specific short-term disability changes among groups of patients with multiple sclerosis.

Abnormally strong functional linkage between cortical areas has been postulated to play a role in the pathogenesis of partial epilepsy. We explore the possibility that such linkages may be manifest in the interictal EEG apart from epileptiform disturbances or visually evident focal abnormalities. We analyzed samples of interictal intracranial EEG (ICEEG) recorded from subdural grids in nine patients with medically intractable partial epilepsy, measuring interelectrode synchrony using the mean phase coherence algorithm. This analysis revealed areas of elevated local synchrony, or 'hypersynchrony' which had persistent spatiotemporal characteristics that were unique to each patient. Measuring local synchrony in a subdural grid results in a map of the cortical surface that provides information not visually apparent on either EEG or structural imaging. We explore the relationship of hypersynchronous areas to the clinical evidence of seizure localization in each case, and speculate that local hypersynchrony may be a marker of epileptogenic cortex, and may prove to be a valuable aid to clinical ICEEG interpretation