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

Transient global amnesia and hippocampal diffusion restriction: an overlooked radiological finding

Transient global amnesia (TGA) is characterized by isolated sudden anterograde amnesia. Diffusion restriction can be observed in the hippocampus on DWI-MRI at varying rates in TGA patients. This study analyzes the prevalence and characteristics of the hippocampal diffusion restriction (HDR), its relationship with vascular risk factors, and the prevalence of lesions overlooked in routine reports. 91 patients diagnosed with TGA at a tertiary hospital between 2011 and 2022 were evaluated retrospectively. The mean age was 64.8 ± 7.3 years, and 63.7% of patients were female. 75.8% of the patients had at least one vascular risk factor. Focal diffusion restriction was detected in 17 patients (18.5%) on DWI-MRI, with only one being extra-hippocampal. 81.2% of HDR was detected when DWI-MRI scan was performed between 12 and 96 h after the onset of symptoms. HDR was detected most when the imaging was performed in 24 to 48 h (p = 0.03). There was no correlation between the duration of symptoms and the detection rates of HDR (p = 0.55). In 9 patients (53% of 17) diffusion restriction was not specified in routine radiology reports. Although focal ischemia, venous flow abnormalities, migraine and epileptic phenomena have been suggested in its etiology, TGA is a clinical condition of which pathophysiology has not been determined clearly. Signal changes observed in DWI-MRI has led to discussions that cerebrovascular etiology may play a role, yet more comprehensive studies are required to prevent and manage TGA. HDRs can be overlooked in routine reports. Therefore, the DWI-MRI images of patients with TGA should be examined vigilantly.

[Transient global amnesia - benign memory blackout]

Transient global amnesia (TGA) is a typical clinical syndrome characterized by acute, predominantly anterograde amnesia. New epidemiological data assume a significantly higher annual incidence than previously assumed, namely around 15 cases per 100,000 people. Those affected, usually over the age of 50, cannot remember new memory content for longer than 30-180 seconds and therefore ask repetitive questions about current events. All other cognitive functions are unimpaired, and everything previously learnt, e.g. driving or cooking, can be carried out. The episodes are self-limiting and by definition subside within 24 hours. At least 10% of those affected will experience 1-5 recurrences in the future. The punctate lesions in the hippocampus, which are found on MRI in at least 50% of patients after 24-72 hours, are distributed 2/3 unilaterally and 1/3 bilaterally. Using 7 Tesla MRI the frequency of detected lesions increases to 90% compared to 50% with 1.5 or 3 Tesla. Beyond the punctiform hippocampal lesions, other memory-related network disorders, including the default network, are also suggested to be involved in the pathomechanism of TGA. TGA etiology and pathophysiology are not known in detail. Vascular, migraine-like, epilepsy-like, and psychogenic mechanisms are discussed. Triggers of the episodes are often physical exertion with a Valsalva character. Management is aimed at identifying the syndrome based on the typical clinical presentation and ruling out possible differential diagnoses with similar symptoms. During the TGA, the usually anxious relatives should be reassured of the benign and inconsequential nature of the episode.

Guideline "Transient Global Amnesia (TGA)" of the German Society of Neurology (Deutsche Gesellschaft für Neurologie): S1-guideline

INTRODUCTION

In 2022 the DGN (Deutsche Gesellschaft für Neurologie) published an updated Transient Global Amnesia (TGA) guideline. TGA is characterized by a sudden onset of retrograde and anterograde amnesia for a period of one to a maximum of 24 h (with an average of 6 to 8 h). The incidence is estimated between 3 and 8 per 100,000 population/year. TGA is a disorder that occurs predominantly between 50 and 70 years.

RECOMMENDATIONS

The diagnosis of TGA should be made clinically. In case of an atypical clinical presentation or suspicion of a possible differential diagnosis, further diagnostics should be performed immediately. The detection of typical unilateral or bilateral punctate DWI/T2 lesions in the hippocampus (especially the CA1 region) in a proportion of patients proves TGA. The sensitivity of MRI is considered higher when performed between 24 and 72 h after onset. If additional DWI changes occur outside the hippocampus, a vascular etiology should be considered, and prompt sonographic and cardiac diagnostics should be performed EEG may help to differentiate TGA from rare amnestic epileptic attacks, especially in recurrent amnestic attacks. TGA in patients < 50 years of age is a rarity, therefore it is mandatory to rapidly search for other causes in particular in younger patients. The cause of TGA is still unknown. Numerous findings in recent years point to a multifactorial genesis. Because the pathomechanism of TGA is not yet clearly known, no evidence-based therapeutic or prophylactic recommendations can be made.

CONCLUSIONS

There is no evidence for chronic sequelae of TGA with respect to cerebral ischemia, chronic memory impairment, or the onset of dementia-related syndromes.

The Man Who Mistook a Hat for His Wife: Case Report of Aortic Dissection Presenting with Acute Hyperfamiliarity for Faces

Acute aortic dissection is a challenging diagnosis for emergency physicians because of its high mortality and wide range of clinical presentations. We report a case of a previously healthy man who presented with hyperfamiliarity for faces syndrome as the predominant symptom of a large type A aortic dissection diagnosed by computed tomography angiography in the emergency department. Different elements of his presentation suggested possible other diagnoses, including transient global amnesia and transient ischemic attack. We discuss how evaluating these other diagnostic possibilities led to the correct diagnosis. Given increasing reports of painless aortic dissection, this case demonstrates the need to consider aortic dissection in patients with acute neurological symptoms.

Transient global amnesia: 7 Tesla MRI reveals more hippocampal lesions with diffusion restriction compared to 1.5 and 3 Tesla MRI

PURPOSE

To assess the ability of 7 T MRI to detect hippocampal DWI lesions in the acute phase of TGA compared to 1.5 T/3 T MRI.

METHODS

Patients with a clinical diagnosis consistent with TGA and a 1.5/3 T MRI underwent an additional 7 T MRI when the 7 T system was available for clinical use, thus serving as their own controls.

RESULTS

Thirteen TGA patients with a median age of 68.5 years (range 46-77 years) were included and imaged at 1.5/3 T (median 17 h after onset of symptoms, range 3-23 h) and 7 T (median 23 h after onset, range 15-46 h). The 7 T MRIs were performed a median of 15 h after the 1.5/3 T MRIs (range 1-28 h). At 1.5/3 T, six patients (46%) were found to have at least one hippocampal DWI-lesions supporting the TGA diagnosis, which increased to 11 patients (85%) when examined at 7 T (p = 0.03). At 1.5/3 T, nine hippocampal DWI lesions were detected, which increased to 19 at 7 T, giving an increased detection rate of 111% (p = 0.002). Both neuroradiologists found the hippocampal DWI lesions at 7 T to have higher conspicuity and be easier to categorize as true findings compared to 1.5/3 T.

CONCLUSION

Seven-Tesla MRI showed both a statistically significant increase in the total number of detected hippocampal DWI lesions and the proportion of patients with at least one hippocampal DWI lesion supporting the TGA diagnosis compared to 1.5/3 T. Clinical use of 7 T will increase the number of patients having their TGA diagnosis supported by MRI, which can be especially useful in patients with negative 1.5/3 T MRI and low clinical certainty.