Transient global amnesia
A patient on anti-hypertensive therapy developed an acute amnesic state on hearing of the sudden death of a relative. CT head was negative. Her recall gradually improved over 24 hours. She displayed no neurological symptoms. MRI head requested to rule out pathology.
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Axial FLAIR images show scattered bilateral white matter hyperintensities typical of ischemic gliosis. An incidental small falcine meningioma is noted anteriorly on the right.
Axial b1000 DWI shows a small focus of signal hyperintensity within the right hippocampus laterally, adjacent to the lateral ventricle. The ADC study shows a focal hypointensity at the same location, confirming diffusion restriction.
Transient global amnesia (TGA) is a temporary loss of short-term memory without other signs of impaired cognition and with absent focal neurological signs. The diagnostic criteria include that the attack should have been witnessed, there was no seizure or head injury, and the symptoms resolve within 24 hours. Common precipitating events include exercise, exposure to cold water and emotional stress. The etiology is unclear.
In one study of 86 patients with TGA, 6 patients showed a solitary punctate focus of restricted diffusion in the mesiotemporal/hippocampal region, and 4 patients had bilateral lesions, giving an overall lesion incidence of 11%. In another study of 203 episodes of TGA presenting to an emergency department, only 16 patients had DWI lesions. However another study using serial DWI on a cohort of TGA patients reported lesions in only 2/31 scanned within hours of the event, but this increased to 26/31 patients (84%) at 48 hours. The timing of the MRI study is therefore very important.
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