What is the pathophysiology of transient global amnesia (TGA)?

Updated: Jul 27, 2018
  • Author: Roy Sucholeiki, MD; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

The precise pathophysiology of transient global amnesia is not clear. The findings reported with positron emission tomography (PET), diffusion-weighted MRI (DWI), single photon emission computed tomography (SPECT) and MR spectroscopy (MRS) have indicated various brain regions that are affected in TGA.

  • On PET and DWI, blood flow to specific brain areas that involve memory appears to be disrupted transiently during TGA. This includes the thalamus and/or mesial temporal structures (in particular the amygdala and hippocampus).

  • Hakan et al demonstrated tiny increases in signal in the left parahippocampal gyrus and splenium of the corpus callosum on DWI in one patient. This method of imaging allows detection of hyperacute ischemic change. Liang et al and Yang et al have also recently used DWI to document tiny lesions in the hippocampus of patients with acute TGA. [1, 2] However, Eustache et al reported a PET study consistent with a spreading depression in the left lateral frontal cortex. This case also featured oligemia in the left occipital cortex. [3] Strupp et al found mainly medial temporal changes on DWI in 7 of 10 patients with TGA. They suggested that cellular edema or spreading depression could be responsible, not just ischemia. [4]

  • Winbeck et al found a significant incidence (10/28) of acute DWI changes in patients with TGA, which is comparable to the TIA group (21/74). Although the patients who presented with a TIA had a higher prevalence of vascular risk factors, those in the TGA group (who had DWI changes) were found to have significantly more carotid atherosclerosis. [5]

  • Nakada et al demonstrated via high-resolution T2-reversed MRI a high incidence of hippocampal cavities compared with their normal or disease controls. The authors conclude that their findings may indicate that TGA can be associated with neuronal loss in the CA1 region of the hippocampus. [6]

  • Generally, the territory of the vertebrobasilar system is most often rendered ischemic and dysfunctional. However, since ischemia typically does not progress to infarction, symptoms are expected to resolve completely.

  • Yamane et al reported rather diffuse cerebral hypoperfusion on SPECT that improved months later upon repeating the test in a patient with TGA. [7] Yang et al also reported hypoperfusion in the cerebellar vermis that recovered by the time of follow-up examination. [1]

  • Bartsch et al found that in 7 patients with TGA, 4 had a diffusion abnormality corresponding with a T2 lesion in the CA-1 sector of the hippocampus. In 3 of these patients, MRS revealed a lactate peak. The authors suggest that this represents an acute stress reaction of this particular area and indicates the pathological substrate of TGA. [8]

Overall, the variety of findings on functional imaging studies may support the notion that TGA is a syndrome with not only a variety of precipitating causes but also of differing mechanisms.


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