[Diffusion-weighted MR imaging in a case of dissociative amnesia]

The differential diagnosis of psychogenic vs. organic amnestic syndromes may cause difficulty in certain cases. Here, we report a case of psychogenic amnesia which occurred after alcohol intoxication and mild head trauma. The initial memory deficit was very severe consisting of near-complete retrograde amnesia and anterograde amnesia covering 12 hours. The deficits resolved within a 4-week period of time. Brain CT and MRI scans revealed two circumscribed lesions of the right temporal lobe which were interpreted as old posttraumatic lesions. To ascertain the diagnosis, diffusion-weighted MR imaging (DWI) and brain perfusion SPECT were performed. The basal temporal lobes neither showed focal changes of perfusion, nor enhanced signal intensity on DWI as has been recently reported in patients with transient global amnesia. Later, the dissociative nature of the disorder could be confirmed by the exploration of recent psychological conflicts and the delayed type of recovery. We regard diffusion-weighted MRI as a powerful means to differentiate acute amnestic syndromes.