Transient global amnesia: Acute SPECT functional imaging and neuropsychological deficits

Abstract

Five patients with transient global amnesia (TGA) were seen clinically and studied neuropsychologically and with SPECT scanning within 24 hours in four and one within 48 hours of the attack. The memory deficits were characteristic of TGA and the magnetic resonance brain scans were normal in all patients. The SPECT scans showed hypoperfusion in the frontal and thalamic regions in all patients. In addition biparietal hypoperfusion was seen in one, parieta occipital in two and unilateral temporal in two patients. Transcranial Doppler studies were performed in three of the five patients and revealed abnormalities of possible relevance in one. Two of the SPECT studies had normalised when repeated at approximately 2 months post ictus. These five patients represent relatively "pure" forms of TGA as they all had normal MRI scans which excluded other disease processes such as subclinical or silent strokes. The frontal hypoperfusion in all five patients is of interest given the role of the frontal lobes in memory processing. Transient global amnesia (TGA) remains a clinical diagnosis of unknown pathophysiology with no corroborative laboratory or radiological test. Despite over one thousand case reports in the literature,1-9 neuropshyhological assessment at time of or immediately after the ictus is limited to less than a dozen cases.1,3-5 Strict definition as recommended by the Oxford criteria was not used in the majority of studies.1 Several functional scanning studies, mainly single photon emission computed tomography (SPECT) reports and one positron emission computed tomography (PET) study, report of thalamic and/or neocortical hypoperfusion with hippocampal, temporal, frontotemporal, thalamus, hemicortical and mesial temporal sites of decreased cerebral blood flow.3,10-19 Functional imaging with SPECT and PET may be useful in elucidating the cause for the most popular proposed mechanisms which include cerebral ischaemia, seizures and migraine. To date 10 such studies have been published describing 13 patients. In these studies, magnetic resonance imaging (MRI) scans were not reported on, or not performed in six studies and were abnormal in a further two. In the remaining two studies MRI scans were performed 10 days and three months post ictus.3, 10-19 This report describes five patients in the acute phase, all with normal MRI scans. To our knowledge, this study represents the largest case series at TGA patients with normal MRI scans but abnormal SPECT scans.