Complete Hippocampal Ischemic Amnestic Syndrome: what is it?

In 2012, a 22-year-old boy was brought to a Massachusetts hospital complaining of leg problems and what was initially considered a high level of confusion. He constantly repeated the same phrases and asked the same questions. After passing several tests, it soon became evident that what was considered confusion was actually severe amnesia.

This had appeared suddenly, being associated with the consumption, the night before admission, of what the young man believed to be heroin. Since then, around 16 similar cases of what has come to be considered a new amnesic syndrome associated with the use of opioids have been detected.

• Related article: "The different types of amnesia (and their characteristics)"

What is this syndrome?

The complete hippocampal ischemic amnestic syndrome, as the doctors who discovered its existence have called it for the moment, is characterized by the presence of the sudden appearance of anterograde amnesia, often shortly after consumption or after surviving an overdose of some type of opiate (heroin and/or fentanyl being the most common).

This means that patients lose the ability to record new information and store it in memory. Beyond the memory problems, those who suffer from this syndrome may have other alterations, but they are not definitive of this syndrome. In some cases there has been an improvement over time (as occurred with the first of known cases), recovering to a great extent the memory capacity to record new information.

At the neuropsychological level, the existence of brain damage has been observed in a very specific area, being this aspect what is most striking (since they do not tend to have large brain lesions in other areas): the greatest damage and the most characteristic of this evident syndrome is the presence of a lesion of great importance in both seahorses, being the lesion bilateral.

Suffering from amnesia due to damage to the hippocampus or to different areas is not that unusual, and it is also known that hypoxia and stroke affect the hippocampus to a greater extent than to other regions, but it is not so simple that the damage occurs in both hippocampuses at the same time in such a sudden way and without any type of trauma that also damages other areas.

Cause?

The causes of the appearance of massive lesions in both hippocampuses and the appearance of this type of amnesia are largely unknown. Despite this, the immediate cause, the trigger, seems to be associated with the previously mentioned use of opioids. In many of the cases, the patients had a history of opioid use. (especially heroin), suffering from a substance abuse disorder, and in some other cases the presence of other drugs such as cocaine, marijuana, amphetamines, hallucinogens or drugs such as benzodiazepines.

Another element to take into account is that most of us are dealing with more or less young patients (between their twenties and their fifties). majority), of which around half of the known cases suffer from some vascular disorder such as hypertension or diabetes. Vascular alterations could facilitate the appearance of ischemia that caused the hippocampal damage, but how they are really related is something little known.

Suffering from a dependency or substance use disorder, in addition to being one of the possible causes or triggers, it can have different repercussions for your health that can complicate your recovery if you continue to use it after the episode amnesic.

• You may be interested in: "Parts of the human brain (and functions)"

A little-known amnestic syndrome

Not much is known about this syndrome, but it has been observed that it is undergoing a certain expansion: since it was observed in 2012 the first case to date, a total of 16 cases have been detected in the United States that meet the same criteria characteristics.

However, we must bear in mind that it is possible that there are more, since there is a possibility that people without resources have not gone to the hospital (These 14 cases have been observed in the United States), or that previous cases have been associated with other disorders.

But apart from the aforementioned findings, little is known about this syndrome. Much more research is needed to determine the causes of this disorder. and establish action and treatment protocols more appropriate to this problem.

Bibliographic references:

• Barash, J.A.; Somerville, N. & DeMaria, A. (2017). Cluster of an unusual amnestic syndrome – Massachusetts, 2012-2016. MMWR.: 66(3); 76-79.
• Duru, U.B.; Pawat, G.; Barash, J.A.; Miller, L.E.; Thiruselvam, I.K. & Haut, M.W. (2018). An Unusual Amnestic Syndrome Associated With Combined Fentanyl and Cocaine Use. Annals of Internal Medicine. American College of Physicians
• Lim, C.; Alexander, M.P.; LaFleche, G.; Schnyer, D.M.; Verfaellie, M. (2004). The neurological and cognitive sequelae of cardiac arrest. Neurology, 63 (10): 1774-1778.