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Unusual Amnesia Cases May Be Linked to Drug Overdoses, Doctors Say

MRI scans of a patient afflicted with ‘complete hippocampal ischemia and amnesia syndrome’ show bright white spots indicating damage to both sides of the hippocampus, a structure essential to creating and storing memories.
Lahey Hospital & Medical Center

Dr. Yuval Zabar, a senior neurologist on staff at the Lahey clinic, spends time with a lot of patients afflicted with memory loss. A few years ago, he was brought in to consult on a patient who had come out of a heroin overdose with a form of amnesia. 

“His brain was basically not recording new information,” Zabar said. The patient would ask questions, and seem to understand the answers, “but then, a very short while after that, he would basically ask the same exact question as though the conversation never happened.”

It’s not necessarily unusual for people who overdose on opiates to experience memory loss. But Zabar thought this particular type of amnesia didn’t make sense for an overdose like this. It wasn’t not so much memory loss as the inability to form new memories, in a sense re-living the same day over and over again. Zabar ordered a more detailed MRI scan of the brain, and he was shocked by what he saw: “Perfectly symmetrical, abnormal…very intense signals in the hippocampus on both sides of the brain.  It's very striking.”

The abnormality is striking even to the untrained eye: two bright white spots indicating damage to both sides of the hippocampus—a small, seahorse-shaped structure that is essential to creating and storing memory. Zabar says it couldn’t have been from a stroke or similar type of vascular injury, because the damage was so specific, affecting just these two particular spots, on opposite sides of the hippocampus, as if they had been targeted.

“We thought he was a unique case and we might never see anything like it again,” Zabar said. So he and his colleague Dr. Jed Barash decided to write a study of the case. 

Before they’d even finished, Barash encountered another patient with the same story: overdose, amnesia, and this very strange, very particular damage to the hippocampus. Then, another two cases. 

“Here we are seeing a case that has never been really described. Now all of a sudden we have four cases in one hospital. So then it became a cluster, and that's when we wrote up the four cases and that's when we reported it to the Massachusetts Department of Public Health,” said Zabar.

Dr. Alfred DeMaria, the medical director of the Department of Public Health’s infectious disease bureau, agreed that the cluster was significant and “seems beyond coincidence.” 

They sent out word to other neurologists in Massachusetts, looking for similar cases of what’s termed complete hippocampal ischemia and amnesia syndrome. 

That resulted in about 25 cases being brought to our attention, of which ten new cases were ultimately identified as having the same syndrome,” said DeMaria.

Now the state has sent out a notice to all doctors to be on the lookout for new cases that match this pattern. DeMaria said the early stages of tracking a disease like this are very difficult, because at this stage, any number of variables could be in play. 

“It may be that this has nothing to do with the substance use.  [Perhaps] it's just coincidental that we're finding these cases because these are the people who were evaluated.” He added that “a number of people who responded to the publication” have mentioned that domoic acid, a toxin found in shellfish, has caused this kind of amnesia in other cases. It could be that opiates in combination with another unknown substance could be causing this syndrome.

But the only thing that’s certain at this point is the effect this kind of brain damage can have. Zabar recalls how that first patient he saw couldn’t function and couldn’t even be left alone safely.  He has improved over the past couple of years, but Zabar says that may not be the case for everyone. 

“Developing an amnestic syndrome early in life if it's irreversible is potentially a disability for the rest of your life, and living independently is probably not in the cards for somebody with a condition like this,” he said.

Zabar and DeMaria say they hope that as doctors across the commonwealth are now on the lookout, they’ll be able to understand and ultimately prevent this devastating condition.


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