Permanent global amnesia with unknown etiology.

Three patients developed severe and selective memory impairment with no known cause, one during a period of a few days and two others during a period of 1 to 2 years. In two of these patients, the amnesia has been stable and circumscribed for 5 to 6 years. The third patient appears to have declined in cognitive functions during the past year, at the age of 78, after 6 years of stable, circumscribed amnesia. Neuropsychological testing reveals severe impairment in the ability to learn verbal and nonverbal material as well as retrograde amnesia covering at least 20 years. CT and routine brain MRIs were uninformative. Subsequently, a high-resolution protocol for imaging human hippocampus with MR revealed that the hippocampal formation was markedly reduced in size in all three patients. The pattern of cognitive impairment and the MR findings are similar to the findings in other patients with chronic amnesia due to a known anoxic or ischemic episode, and differ from the findings in amnesic patients with alcoholic Korsakoff's syndrome. We suggest that the amnesia may be due to ischemic damage to medial temporal lobe brain structures important for memory.