Unexplained sudden amnesia.

BACKGROUND In almost all cases of acute, sudden, persistent amnesia, the cause can be determined. Ischemic stroke, hypoglycemia, syncope, and seizure are the most likely causes. PATIENTS AND METHODS In a clinical study, 2 elderly men are described in which sudden, permanent amnesia developed in the absence of a satisfactory explanation. In 1 case, a neuropathologic study disclosed Alzheimer disease; in the other, magnetic resonance imaging showed a temporal lobe abnormality bilaterally. RESULTS A man aged 80 years suddenly lost his memory of the previous 60 years. Neuropathologic study 5 years later showed the changes of Alzheimer disease. In the second case a disabling amnesia developed overnight in a man aged 70 years. There was no progression of the disabling amnesia in the next 15 years. Magnetic resonance imaging 10 years from the onset showed abnormality of the medial temporal lobe bilaterally. CONCLUSIONS In neither case was the amnesia satisfactorily explained. It is likely that rare cases of amnesia occur as the result of an unrecognized pathophysiologic process.