Although no lesions were identified on immediate imaging, hippocampal lesions were found one to two days after an episode of transient global amnesia in over 80 percent of studied patients, according to an article in the June 22nd issue of Neurology.

A German research team used diffusion weighted imaging, a type of magnetic resonance imaging, to examine 31 patients within hours of the onset of amnesia. In a new approach, the patients underwent two follow-up studies over the next two days. After 24 hours, small lesions appeared for 23 patients, and after 48 hours, lesions appeared for 3 more patients (total of 26/31, 84 percent). All lesions were located in the hippocampus, an area of the brain which plays an important role in memory functions. In two of the five patients without lesions, the imaging study was done after 96 and 120 hours.

Transient global amnesia is characterized by a sudden inability to form new memories or recall the near past. This amnesia often occurs following a stressful, emotional situation, and usually lasts less than 24 hours. There are no apparent long-term effects. The cause isn’t yet known. None of the patients studied had recent history of head injury or seizures.

Despite some similarities, transient global amnesia isn’t the same as a transient ischemic attack. Lesions from transient ischemic attacks typically appear larger in size and without delay, in contrast to lesions associated with transient global amnesia.

“Lesions were rarely noted during the period of amnesia, but with follow-up magnetic resonance imaging (MRI), they became visible by 48 hours,” said study author Oliver L. Sedlaczek, MD. “Our study confirms the involvement of hippocampal lesions in transient global amnesia. The delayed detectability of lesions may explain the incongruence of previous studies in this condition.”

The study results could influence treatment of individuals with transient global amnesia. Antiplatelet therapy could be considered in those with vascular risk factors such as arteriosclerosis, commented David C. Tong, MD, who wrote an editorial in the same issue of Neurology.

“Using this study as a stepping stone, perhaps we can further clarify the mechanism of this condition by combining these findings with perfusion weighted MRI, functional neuroimaging such as PET or SPECT, and possibly venography,” said Tong.

One potential area to continue study is metabolic rate, noted Sedlaczek.
“Emotional arousal has been suggested to lead to metabolic disturbances,” said Sedlaczek. “High metabolic rates leading to a relative insufficiency of blood flow in the hippocampus could be the natural history of transient global amnesia.”