Imaging Onset and Propagation of ECT‐induced Seizures

Abstract

Summary:Purpose: Regions of seizure onset and propagation in human generalized tonic-clonic seizures are not well understood. Cerebral blood flow (CBF) measurements with single photon emission computed tomography (SPECT) during electroconvulsive therapy (ECT)-induced seizures provide a unique opportunity to investigate seizure onset and propagation under controlled conditions.Methods: ECT stimulation induces a typical generalized tonic-clonic seizure, resembling spontaneous generalized seizures in both clinical and electroencephalogram (EEG) manifestations. Patients were divided into two groups based on timing of ictal (during seizure) SPECT tracer injections: 0 s after ECT stimulation (early group), and 30 s after ECT (late group). Statistical parametric mapping (SPM) was used to determine regions of significant CBF changes between ictal and interictal scans on a voxel-by-voxel basis.Results: In the early injection group, we saw increases near the regions of the bitemporal stimulating electrodes as well as some thalamic and basal ganglia activation. With late injections, we observed increases mainly in the parietal and occipital lobes, regions that were quiescent 30 s prior. Significant decreases occurred only at the later injection time, and these were localized to the bilateral cingulate gyrus and left dorsolateral frontal cortex.Conclusions: Activations in distinct regions at the two time points, as well as sparing of intermediary brain structures, suggest that ECT-induced seizures propagate from the site of initiation to other specific brain regions. Further work will be needed to determine if this propagation occurs through corticalcortical or cortico-thalamo-cortical networks. A better understanding of seizure propagation mechanisms may lead to improved treatments aimed at preventing seizure generalization.

The Default Mode Network and Altered Consciousness in Epilepsy

“…SPECT studies of ECT-induced seizures in depression patients have revealed significant CBF decreases in the bilateral anterior and posterior cingulate gyrus and precuneus [7,21] in addition to decreases in the medial frontal and lateral parietal lobes [9]. These findings were largely recapitulated in a subsequent study of a large group of epilepsy patients, which reported ictal and post-ictal CBF decreases in the precuneus and cingulate gyrus and postictal CBF decreases in the lateral frontoparietal association cortex [14].…”

“…SPECT studies have revealed that the earliest increases are often in the temporal lobe, where tonic-clonic seizures most commonly originate [14,68]. Additionally, large CBF increases during the generalization phase have been observed in the bilateral medial and lateral parietal cortex [9,21] as well as in the thalamus, basal ganglia, and superior medial cerebellum [9,14,21]. Interestingly, we recently observed that during the post-ictal phase, CBF in the bilateral lateral cerebellar hemispheres continues to increase before returning to a baseline level [14].…”

“…However, ictal single photon emission computed tomography (SPECT) works by injection of radiopharmaceutical during the seizure; and imaging at a later time can provide a window into changes in cerebral blood flow during seizures, a known marker of neuronal activity. Additionally, intracranial electroencephalography (EEG) [62] and electroconvulsive therapy (ECT) studies have proven useful for understanding these events [7,9,21].…”

Mode of action of electroconvulsive therapy: an update

“…In contrast, single photon emission computed tomography (SPECT) is par ticularly well suited to the investigation of rCBF during seizures. A collaboration among neurolo gists and psychiatrists at Yale University School of Medicine suggested hypotheses to explain both the reduced clinical efficacy of right unilateral ECT and the reduced effect on verbal memory (Enev 2007). It would have been informative to compare threshold right unilateral ECT with threshold bilateral ECT, but threshold right unilateral ECT was not included.…”

“…Bilateral ECT produced robust increases of blood flow symmetrically in frontal and temporal regions of the brain. In right unilateral ECT, the relative sparing of the left temporal lobe was the likely explanation of the reduced impair ment of verbal memory, and the relative sparing of the left cortical and subcortical regions was the likely explanation of the reduced clinical efficacy (Enev 2007). More will be said about the putative neuroanatomy of major depression below.…”