Biomedical subjects

Peter D Williamson

Publications and source records attributed to Peter D Williamson.

4 recordsLinked to original sources

PubMed2005

Frontal lobe seizures.

Despite the fact that clinical characteristics of frontal lobe seizures have been recently described better, differentiating seizures of frontal lobe origin from NES on clinical grounds alone is difficult. The difficulty has been compounded by the fact that both inter-ictal and ictal EEG can be normal or nonspecific, and the same is true of imaging studies. A detailed clinical history as well as video monitoring can be helpful diagnostic tools. A multidisciplinary approach is warranted and is at times essential to improve the diagnosis and care of these difficult patients.

Chromosomes, Human, Pair 1↗

PubMed2003

Validation of ictal single photon emission computed tomography with depth encephalography and epilepsy surgery.

Many centers have reported that ictal single photon emission computed tomography (SPECT) localizes regions of seizure onset with greater sensitivity and specificity than interictal SPECT. Here we report interictal and ictal SPECT scan results in both lesional and nonlesional cases. Using technetium hexamethyl propylamenamine oxide (HMPAO) or ethyl cysteinate dimer (ECD), these scans were done in 52 patients with partial and secondarily generalized seizures. Twenty-five had normal MRI and 27 showed structural lesions. None had mesial temporal sclerosis clearly identified on MRI. All 52 subsequently had interictal and ictal intracranial EEG studies that appeared to localize the seizure focus. Thirty-nine patients had surgery and have been followed for 2 or more years. Interictal SPECT scans showed focal hypoperfusion consistent with intracranial EEG localization of the seizure focus in 29% of patients. In another 13%, there was correct lateralization but not localization. Ictal SPECT scans showed focal hyperperfusion consistent with intracranial EEG localization of the seizure focus in 52% of patients. In another 25%, there was correct lateralization but not localization. The presence or absence of structural lesions on MRI did not affect ictal hyperperfusion or its correlation with intracranial EEG. Thirty-nine patients had resective surgery, of whom 62% had class I outcomes. There was a trend towards better outcome when ictal SPECT data were concordant with intracranial EEG data. The presence or absence of structural lesions on MRI did not affect the likelihood of class I outcome. Ictal SPECT is superior to interictal SPECT in localizing and lateralizing seizure foci. Its results correlate well with intracranial EEG, but in more than one third of cases, the latter shows focal seizure onset in areas that do not show focal hyperperfusion. Surgical outcome tends to be better when the two modalities give concordant results.

Adolescent↗

PubMed2003

Statistical mapping of scalp-recorded ictal EEG records using wavelet analysis.

PURPOSE: The wavelet transform (WT) is well suited for the analysis of signals whose characteristics vary rapidly over time. We devised a computerized method for objective scoring of scalp-recorded seizures that takes advantage of the WT. METHODS: Using wavelet coefficients as a metric, we devised a statistical scoring method aimed at detecting significant and sustained rhythmic buildup. The approach was used to create spatiotemporal significance maps for each seizure. Each seizure was also independently analyzed by computer and an expert reader not involved in the clinical workup or computer analysis of these patients. Hierarchical decision rules for determining seizure lateralization and localization were established from a training set of seizures and subsequently tested on those from an independent test set of seizures. The test dataset included a total of 57 scalp-recorded seizures from 18 patients, each with a > or =12-month seizure-free surgical outcome. RESULTS: Validation was determined by the site of surgical resection. Of the 57 seizure records in the test dataset, the computerized approach resulted in 48 correctly lateralized seizures as compared to 34 for the expert reader. Further, the computer correctly localized 41 seizures to the expert's 31. CONCLUSIONS: The method presented appears to provide an objective basis for the intrachannel scoring of ictal EEGs with minimal interference from artifacts and intermittent discharges. Although the approach has so far shown a substantial improvement over expert scoring in estimating the lateralization and locus of seizure onset, further testing is required to fully evaluate fully its diagnostic accuracy.

Brain Mapping↗

PubMed2003

Does asymmetric basal ganglia or thalamic activation aid in seizure foci lateralization on ictal SPECT studies?

UNLABELLED: Basal ganglia or thalamic activation has been reported in ictal SPECT studies of patients with intractable epilepsy. We hypothesized that lateralization of activation of these subcortical structures may aid in the lateralization of seizure foci in patients in whom the cortical focus is subtle or equivocal. METHODS: This was a retrospective analysis of 72 ictal (99m)Tc-ethylcysteinate dimer SPECT studies in 43 patients with intractable epilepsy in whom seizure laterality could be eventually determined. All patients underwent video-electroencephalography (EEG) monitoring, MRI, and one or more ictal SPECT scans as well as an interictal SPECT scan. Intracranial electrode EEG monitoring and surgery were performed as clinically indicated. Ictal and interictal studies were coregistered with patients' MRI scans using automated software, and ictal minus interictal subtraction images were obtained. The presence of asymmetric basal ganglia or thalamic activation was determined by 2 experienced observers who were unaware of clinical information. The final seizure focus was determined by surgical cure in 37 patients. In patients in whom surgery was not indicated or initial surgery was performed at another institution (n = 6), a consistent focus detected by intracranial electrode monitoring or repeated stereotypical seizures all originating from the same site on video-surface EEG monitoring was considered to indicate the final seizure focus. RESULTS: Thirty-five patients had neocortical seizures and 8 had mesial temporal lobe seizures. Asymmetric basal ganglia activation was seen in 22 (30.6%) studies. This activation was ipsilateral to the final determined seizure focus in 17 of 22 of these studies (77.3%) and contralateral in 5 of 22 (21.7%). Asymmetric thalamic activation was seen in 15 studies (20.8%), of which 12 of 15 (80%) were ipsilateral to the final seizure focus, whereas 3 of 15 (20%) were contralateral. In 3 of 5 studies with contralateral basal ganglia activation and 1 of 3 studies with contralateral thalamic activation, the SPECT study as a whole was found to be falsely localizing. In another 2 cases of contralateral subcortical activation, the SPECT study as a whole was considered nonlocalizing. Worse outcome was not observed in patients with false ictal SPECT subcortical lateralization; however, the presence of asymmetric subcortical uptake, regardless of relationship to seizure focus, was associated with decreased incidence of seizures at 1 y after surgery. CONCLUSION: Although asymmetric basal ganglia or thalamic activation is common, it is rarely the sole indicator of seizure localization. However, it may be a useful confirmatory sign in subtle cases of cortical localization. In cases of false ictal SPECT subcortical lateralization, the basal ganglia appear to follow cortical activation pattern. Furthermore, there appears to be a correlation between lateralizing uptake in subcortical structures on ictal SPECT and postsurgical outcome in intractable epilepsy patients.

Adult↗