Provoked ictal SPECT in temporal and extratemporal drug-resistant epileptic patients: Comparison of Statistical Parametric Mapping and qualitative analysis

Advances in the development of biomarkers for epilepsy

Over 50 million people worldwide have epilepsy. In nearly 30% of these cases, epilepsy remains unsatisfactorily controlled despite the availability of over 20 antiepileptic drugs. Moreover, no treatments exist to prevent the development of epilepsy in those at risk, despite an increasing understanding of the underlying molecular and cellular pathways. One of the major factors that have impeded rapid progress in these areas is the complex and multifactorial nature of epilepsy, and its heterogeneity. Therefore, the vision of developing targeted treatments for epilepsy relies upon the development of biomarkers that allow individually tailored treatment. Biomarkers for epilepsy typically fall into two broad categories: diagnostic biomarkers, which provide information on the clinical status of, and potentially the sensitivity to, specific treatments, and prognostic biomarkers, which allow prediction of future clinical features, such as the speed of progression, severity of epilepsy, development of comorbidities, or prediction of remission or cure. Prognostic biomarkers are of particular importance because they could be used to identify which patients will develop epilepsy and which might benefit from preventive treatments. Biomarker research faces several challenges; however, biomarkers could substantially improve the management of people with epilepsy and could lead to prevention in the right person at the right time, rather than just symptomatic treatment.

Optimizing SPECT SISCOM analysis to localize seizure-onset zone by using varying z scores

PURPOSE

Subtraction ictal single photon emission computed tomography (SPECT) co-registered to magnetic resonance imaging (MRI) (SISCOM) is a useful modality to identify epileptogenic focus. Using this technique, several studies have generally considered the area of highest ictal hyperperfusion, as outlined by thresholding the difference images with a standard z score of 2, to be highly concordant to the epileptogenic focus. In clinical practice, several factors influence ictal hyperperfusion and using different SISCOM thresholds can be helpful. We aimed to systematically evaluate the localizing value of various z scores (1, 1.5, 2, and 2.5) in a seizure-free cohort following resective epilepsy surgery, and to examine the localizing information of perfusion patterns observed at each z score.

METHODS

Twenty-six patients were identified as having ictal-interictal SPECT images, preoperative and postoperative MRI studies, and having remained seizure free for at least 6 months after temporal or extratemporal surgical resection. SISCOM analysis was performed using preoperative MRI studies, and then blindly reviewed for localization of hyperperfused regions. With the added information from postoperative, coregistered MRI, perfusion patterns were determined.

KEY FINDINGS

Using pair-wise comparisons, we found that the optimal z score for SPECT-SISCOM localization of the epileptogenic zone was 1.5, not the commonly used z score of 2. The z score of 1.5 was 84.8% sensitive and 93.8% specific. The z score of 1.5 had a moderate interrater agreement (0.70). When an hourglass configuration hyperperfusion pattern was present, a trend toward correctly localizing the seizure onset region was suggested (100% of the 11 observed occurrences). Nonetheless this trend was not statistically significant, possibly reflecting the small number of occurrences in our study.

SIGNIFICANCE

SISCOM is a useful modality in evaluating patients for epilepsy surgery. This study shows that the z score of 1.5 represents a highly sensitive and specific SISCOM threshold that should be examined in conjunction with the traditionally used z score of 2 to enhance the chances of correct localization. Further prospective investigations are needed to confirm this finding in large patient series.

Statistical parametric mapping of interictal 123I-iomazenil SPECT in temporal lobe epilepsy surgery

Brain single photon emission computed tomography (SPECT) for epilepsy is divided into two types (using three radionuclide tracers)-perfusion SPECT (123I-IMP or 99 mTc-ECD), identifying epileptogenic foci by detecting abnormality in regional cerebral blood flow, and 123I-iomazenil SPECT, identifying epileptogenic foci based on distribution of central benzodiazepine receptors. This study aimed to statistically evaluate and compare the SPECT effectiveness for the three tracers. Statistical parametric mapping (SPM) analysis was performed on 30 mesial temporal lobe epilepsy (mTLE) patients. The radionuclide and patient data were categorized as follows: abnormality in the medial temporal lobe on the operated hemisphere (AAA), in the entire temporal lobe on the operated hemisphere (AA), in the dominantly affected temporal lobe on the operated hemisphere (A), in bilateral temporal lobes (B), with no abnormalities in bilateral temporal lobes (C), and with abnormality in the temporal lobe on the nonoperated hemisphere (D). For analyses of (AAA), (AA), and (A), examining the hemisphere containing epileptogenic foci, IMP-SPECT was significantly superior to ECD-SPECT (P<0.05). For (AAA), indicating localization, IMZ-SPECT was significantly superior to the other two (P<0.05). IMP-SPECT was superior for lateralizing and IMZ-SPECT was useful for localizing epileptogenic foci in mTLE patients though the applicability of the results in extratemporal lobe epilepsy is unknown.

Preictal changes in cerebral haemodynamics: review of findings and insights from intracerebral EEG

The possibility of recording changes in brain signals occurring before epileptic seizures is of considerable interest, both as markers for seizure anticipation and as a window into the mechanisms of seizure generation. Several studies have reported preictal changes on electrophysiological traces. More recently, observations have been made of changes occurring on haemodynamic signals before interictal events or before seizures, often without concurrent changes observed on electrophysiology. We present here a critical review of these findings, in optical imaging, SPECT and fMRI, followed by a discussion based on data from intracerebral EEG.