Hippocampal modifications in transient global amnesia

Identification of Polymorphisms in EAAT1 Glutamate Transporter Gene SLC1A3 Associated with Reduced Migraine Risk

Dysfunction in ion channels or processes involved in maintaining ionic homeostasis is thought to lower the threshold for cortical spreading depression (CSD), and plays a role in susceptibility to associated neurological disorders, including pathogenesis of a migraine. Rare pathogenic variants in specific ion channels have been implicated in monogenic migraine subtypes. In this study, we further examined the channelopathic nature of a migraine through the analysis of common genetic variants in three selected ion channel or transporter genes: SLC4A4, SLC1A3, and CHRNA4. Using the Agena MassARRAY platform, 28 single-nucleotide polymorphisms (SNPs) across the three candidate genes were genotyped in a case-control cohort comprised of 182 migraine cases and 179 matched controls. Initial results identified significant associations between migraine and rs3776578 (p = 0.04) and rs16903247 (p = 0.05) genotypes within the SLC1A3 gene, which encodes the EAAT1 glutamate transporter. These SNPs were subsequently genotyped in an independent cohort of 258 migraine cases and 290 controls using a high-resolution melt assay, and association testing supported the replication of initial findings-rs3776578 (p = 0.0041) and rs16903247 (p = 0.0127). The polymorphisms are in linkage disequilibrium and localise within a putative intronic enhancer region of SLC1A3. The minor alleles of both SNPs show a protective effect on migraine risk, which may be conferred via influencing the expression of SLC1A3.

Transient global amnesia - hippocampal lesions in magnetic resonance imaging

BACKGROUND

Transient global amnesia is a benign syndrome characterized by a sudden onset loss of anterograde amnesia with full recovery. Magnetic resonance of the brain including diffusion-weighted imaging of patients with transient global amnesia revealed the presence of punctate hyperintense signal abnormalities in the hippocampus.

OBJECTIVE

Analysis of the presence of hippocampal lesions in brain magnetic resonance imaging in patients with transient global amnesia and the possible influence of additional factors on their appearance.

METHODS

In this retrospective, an observational study we assessed brain magnetic resonance imaging in 38 consecutive patients with transient global amnesia. The incidence of brain magnetic resonance imaging lesions was analyzed for the coexisting cardiovascular risk factors and precipitating events.

RESULTS

Hippocampal brain magnetic resonance imaging lesions were detected in 47% of patients with transient global amnesia. Of those, 65% had unilateral lesions, 82% were left-sided, and 28% were right-sided. Most lesions were located in the CA1 subfield. The incidence of hypertension in patients with transient global amnesia was higher than in the general population. Stress and exercise preceded the onset of transient global amnesia only in 13% and 16% of patients, respectively. There was no higher incidence of migraine in transient global amnesia patients (13%).

CONCLUSIONS

We found that nearly 50% of patients with transient global amnesia had hyperintense hippocampal brain magnetic resonance imaging lesions. In addition to hypertension, individuals with transient global amnesia had similar cardiovascular risk factors as the general population. We did not identify any precipitating events prior to the onset of transient global amnesia.

Disruption in normal correlational patterns of metabolic networks in the limbic circuit during transient global amnesia

Transient global amnesia is characterized by the sudden apparition of severe episodic amnesia, mainly anterograde, associated with emotional changes. Even though the symptoms are stereotyped, cerebral mechanism underlying transient global amnesia remains unexplained and previous studies using positron emission tomography do not show any clear results or consensus on cerebral regions impacted during transient global amnesia. This study included a group of 10 transient global amnesic patients who underwent ¹⁸F-fluorodeoxyglucose positron emission tomography during the acute or recovery phase of the episode and 10 paired healthy controls. Episodic memory was evaluated with the encoding-storage-retrieval paradigm and a story recall test of the Wechsler's memory scale and anxiety was assessed with the Spielberger scale. We used statistical parametric mapping to identify modifications of whole-brain metabolism. Regarding hypometabolism, there was no brain region systematically affected in all transient global amnesic patients and the comparison between amnesic patients and controls did not show any significant differences. To better understand the specific implication of the limbic circuit in the pathophysiology of transient global amnesia, we then conducted a correlational analysis that included regions of this network. Our findings showed that in healthy controls, regions of the limbic circuit seem to operate in a synchronized way with all regions being highly correlated to each other. On the opposite, in transient global amnesic patients, we observed a clear disruption of this normal correlational patterns between regions with the medial temporal lobe (the hippocampus, parahippocampal gyrus and amygdala) included in one cluster and the orbitofrontal cortex, anterior and posterior cingulate gyrus and thalamus gathered in the other one. Given the individual variability in the time course of transient global amnesia, the direct comparison between a group of patients and controls does not seem to favour the identification of subtle and transient alterations in regional metabolism. The involvement of an extended network, such as the limbic circuit, seems more likely to explain the symptoms of patients. Indeed, the synchronization of regions within the limbic circuit seems to be altered during transient global amnesia, which could explain the amnesia and anxiety observed in transient global amnesic patients. The present study thus deepens our understanding of the mechanisms underlying not only amnesia but also the emotional component of transient global amnesia by considering it as a disruption in the normal correlational patterns within the limbic circuit.

EPIAMNE: A New Scoring System for Differentiating Transient EPIleptic AMNEsia from Transient Global Amnesia

Transient epileptic amnesia (TEA) is a rare cause of acute amnestic syndromes (AAS), often misdiagnosed as transient global amnesia (TGA). We proposed a scoring system—the EPIlepsy AMNEsia (EPIAMNE) score—using quantitative EEG (qEEG) analysis to obtain a tool for differentiating TEA from TGA. We retrospectively reviewed clinical information and standard EEGs (stEEG) of 19 patients with TEA and 21 with TGA. We computed and compared Power Spectral Density, demonstrating an increased relative theta power in TGA. We subsequently incorporated qEEG features in EPIAMNE score, together with clinical and stEEG features. ROC curve models and pairwise ROC curve comparison were used to evaluate and compare the diagnostic accuracy for TEA detection of EPIAMNE score, presence of symptoms atypical for TGA (pSymAT) and identification of anomalies (interictal epileptiform or temporal focal spiky transients) at stEEG (PosEEG). Area Under the Curve (AUC) of EPIAMNE score revealed to be higher than PosEEG and pSymAT (AUCEPIAMNE = 0.95, AUCpSymAT = 0.85, AUCPosEEG = 0.67) and this superiority proved to be statistically significant (p-valueEPIAMNE-PosEEG and p-valueEPIAMNE-pSymAT < 0.05). In conclusion, EPIAMNE score classified TEA with higher accuracy than PosEEG and pSymAT. This approach could become a promising tool for the differential diagnosis of AAS, especially for early TEA detection.

Neuroimaging and Electroencephalographic Correlation in Patients with Transient Global Amnesia: Clinical Case Series

Objective. To determine if there is any correlation between the electroencephalographic and neuroimaging findings in patients with Transient Global Amnesia (TGA). Methods: We retrospectively reviewed files of the First Department of Neurology of AHEPA University Hospital, including patients with a clinical diagnosis of TGA. Only patients who had the characteristic high signal in the temporal lobes in the DWI MRI and those who underwent electroencephalographic recording (EEG) were selected. Results: Out of 28 patients, 8 were selected. We found that 6 out of 8 patients (75%) who had imaging findings in DWI, in at least one medial temporal lobe, also had had intermittent slow theta waves on the electroencephalographic recording. Of these 6 patients, 3 (50%) had bilateral EEG findings, 2 patients (33,3%) only had findings on the left hemisphere and 1 (17%) had on the right hemisphere. 3 out of 6 patients (50%) had electroencephalographic dominance on the left, while 2 out of the 6 (33%) had on the right. In 2 patients with imaging findings in DWI no anomalies were demonstrated on EEG. In 3 out of 8 patients, both MRI and EEG findings correlated on the same side, while 1 patient had opposite findings, depending on which hemisphere the EEG anomalies dominated. Conclusions: There is no absolute matching between the DWI MRI and EEG findings in patients with the clinical diagnosis of TGA. However, there is some degree of correlation, when we focus on the focal dominance of the EEG anomalies, although not statistically significant.

Sensitivity of diffusion-weighted magnetic resonance imaging in transient global amnesia as a function of time from symptom onset

BACKGROUND

The objective was to systematically evaluate the sensitivity of diffusion-weighted magnetic resonance imaging (DW-MRI) for transient global amnesia (TGA) across various time frames compared to the reference-standard clinical criteria.

METHODS

All indexed publications related to TGA and MRI through June 2020 were retrieved by a medical librarian. Two independent reviewers identified original research studies of adults with a clinical diagnosis of TGA using Caplan and Hodges and Warlow criteria (reference standard) who were evaluated with DW-MRI. Pooled estimates and its 95% confidence intervals (CI) for the proportion of acute TGA patients with positive DW-MRI (i.e., sensitivity) were obtained using random-effects meta-analysis for various time frames. Quality assessment was performed using the revised Quality of Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool.

RESULTS

After screening 665 reports, we identified 81 potentially relevant studies. Twenty-three studies representing 1688 patients met eligibility criteria, but not all studies had data available for meta-analysis. The pooled sensitivity (also described as positivity rate) of DW-MRI was 15.6% (95% CI = 2.6%-35.0%) between 0 and 12 h from symptom onset, 23.1% (95% CI = 6.1%-45.7%) at 0-24 h, 72.8% (95% CI = 40.8%-96.3) at 12-24 h, 68.8% (95% CI = 44.8%-88.8%) at 24-36 h, 72.4% (95% CI = 59.8%-83.5%) at 36-48 h, 82.8% (95% CI = 54.7%-99.6%) at 48-60 h, 66.9% (95% CI = 47.5%-83.9%) at 60-72 h, and 72.0% (95% CI = 30.1%-100.0%) at 72-96 h. There was significant concern for risk of bias in the QUADAS-2 domains of patient selection and index test, yielding a low level of certainty in the pooled estimates.

CONCLUSION

DW-MRI lesions are uncommon in patients with TGA early after symptom onset, but the sensitivity (i.e., positivity rate) of DW-MRI increases with time. Despite the limited quality of existing evidence, obtaining an early DW-MRI in patients with clinical diagnosis of TGA in the acute setting is likely a low-yield test.

Transient Global Amnesia - Risk Factors and Putative Background

Objectives

Transient global amnesia (TGA) is a temporary short-term reversible memory loss. Etiology of TGA remains unclear with various hypotheses. We analyzed clinical characteristics, neuroimaging, and electrophysiological findings as well as comorbidities and seasonal variation in TGA patients with regard to possible background of the syndrome.

Materials and Methods

A total of 56 patients (42 women and 14 men) with TGA hospitalized from 2008 to 2016 in the Department of Neurology, Wrocław Medical University.

Results

A total of 52 patients (92.9%) underwent their first-ever episode of TGA. The potential triggers or events before episode could be recognized in 22 patients (39.3%). 35.7% patients had TGA in summer and 26.8% in winter months. In 92.9% patients chronic diseases were found, included: Hypertension (60.7%), dyslipidemia (48.2%), autoimmune thyroiditis (17.9%), and ischemic heart disease (14.3%). One patient (1,8%) suffered from migraine. Doppler ultrasonography of carotid arteries revealed abnormalities in 29 patients (51.8%). Electroencephalography abnormalities were observed in 10 (17.6%) of patients.

Conclusion

Our findings suggest a putative cerebrovascular background of transient global amnesia. No evidence has been provided for the association between TGA and epilepsy or migraine. Among comorbidities, autoimmune thyroiditis deserves further investigation with regard to its potential links with TGA.

Migraine in transient global amnesia: a meta-analysis of observational studies

BACKGROUND

PURPOSE: Although many studies have investigated the relationship between transient global amnesia (TGA) and migraine, to date, no meta-analysis has confirmed the existence and size of their association.

METHODOLOGY

Literature search involved MEDLINE, EMBASE, CENTRAL and PsycINFO. Observational controlled studies including TGA patients (Caplan, Hodges and Warlow) were retrieved. Quality evaluation was based on the Newcastle-Ottawa scale. The prevalence of migraine was compared in TGA patients vs. healthy controls (HC), as well as in TGA against TIA individuals. Data from case-control, cross-sectional and cohort studies were pooled separately.

RESULTS

Literature search yielded 1178 articles, 12 of which were included in the present meta-analysis. Results from case-control (ten), cohort (one) and cross-sectional (one) studies were compatible with an association between TGA and migraine. The nationwide inpatient cross-sectional study was of lesser value due to its inpatient orientation. The high-quality, population-based, retrospective cohort (158,301 participants per group) determined a higher relative-risk (RR) of TGA for migraine vs. non-migraine individuals [RR = 2.48, 95%confidence-interval (95% CI) = (1.32, 4.87)]. Sensitivity testing based on stricter diagnostic criteria strengthened the estimated association [RR = 3.84, 95% CI = (1.57, 9.38)]. Additionally, pooled data from eight case-control studies (700 TGA, 746 HC) yielded similar results [Odds-Ratio, OR = 2.51, 95% CI = (1.85, 3.41)], with the association mainly driven by the three high-quality studies, rather than the five articles of moderate quality. Finally, pooled findings from four case-control studies of moderate-quality revealed a higher prevalence of migraine among TGA compared to TIA patients [OR = 1.82, 95% CI = (1.22, 2.73)].

CONCLUSIONS

A significant association between TGA and migraine was established. The underlying connecting mechanism remains undetermined, yet.

Optimization of magnetic resonance imaging protocol for the diagnosis of transient global amnesia

Objective

To emphasize the most appropriate magnetic resonance imaging (MRI) diffusion protocol for the detection of lesions that cause transient global amnesia, in order to perform an accurate examination, as well as to determine the ideal time point after the onset of symptoms to perform the examination.

Materials and Methods

We evaluated five patients with a diagnosis of transient global amnesia treated between 2012 and 2015. We analyzed demographic characteristics, clinical data, symptom onset, diffusion techniques, and radiological findings. Examination techniques included a standard diffusion sequence (b value = 1000 s/mm²; slice thickness = 5 mm) and a optimized diffusion sequence (b value = 2000 s/mm²; slice thickness = 3 mm).

Results

Brain MRI was performed at 24 h or 36 h after symptom onset, except in one patient, in whom it was performed at 12 h after (at which point no changes were seen) and repeated at 36 h after symptom onset (at which point it showed alterations in the right hippocampus). The standard and optimized diffusion sequences were both able to demonstrate focal changes in the hippocampi in all of the patients but one, in whom the changes were demonstrated only in the optimized sequence.

Conclusion

MRI can confirm a clinical hypothesis of transient global amnesia. Knowledge of the optimal diffusion parameters and the ideal timing of diffusion-weighted imaging (> 24 h after symptom onset) are essential to improving diagnostic efficiency.