New insights into a mysterious type of amnesia

Jun 21 2004

Researchers have new insights into a mysterious type of amnesia, according to a study published in the June 22 issue of Neurology, the scientific journal of the American Academy of Neurology. The study showed lesions didn’t appear immediately in the patients’ brains, but developed one to two days after an episode of transient global amnesia.

Using diffusion weighted imaging, a type of MRI, a team in Germany examined 31 patients within hours of the onset of amnesia. In a new approach, the patients underwent two follow-up MRI studies over the next two days. After 24 hours, small lesions (areas of brain damage) appeared on the MRI for 23 patients, and after 48 hours, lesions appeared for three more patients. 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 MRI 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 (TIA). Lesions from TIA 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 MRI, they became visible by 48 hours,” said study author Oliver L. Sedlaczek, MD, of the Department of Neurology at University of Heidelberg in Mannheim, Germany. “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, of Stanford University School of Medicine in Stanford, Calif., 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.”

The American Academy of Neurology, an association of more than 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as epilepsy, dystonia, migraine, Huntington’s disease, and dementia.

For more information about the American Academy of Neurology, visit its website at http://www.aan.com.