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ublic health officials on Thursday said they had detected a bizarre cluster of cases in which patients in Massachusetts developed amnesia over the past few years — a highly unusual syndrome that could be connected to opioid use.

The officials have identified only 14 cases so far. But officials said it’s possible that clinicians have simply missed other cases.

The patients were all relatively young — they ranged in age from 19 to 52. Thirteen of the 14 patients identified had a substance use disorder, and the 14th patient tested positive for opioids and cocaine on a toxicology screen.

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“What we’re concerned about is maybe a contaminant or something else added to the drug might be triggering this,” said Dr. Alfred DeMaria, the state epidemiologist at the Massachusetts Department of Public Health and an author of the new report. “Traditionally there’s no evidence that the drugs themselves can do this.”

The pattern emerged when Dr. Jed Barash, a neurologist at Lahey Hospital and Medical Center in Burlington, Mass., reported four of the amnesia cases to the state’s public health department. The department then sent out an alert to specialists, including neurologists and emergency physicians, asking about similar cases, ultimately identifying 10 more from 2012 to 2016 at hospitals in eastern Massachusetts. (The patients included one person who lived in New Hampshire and one person who was visiting Massachusetts from Washington state.)

The patients experienced various memory problems affecting both long- and short-term memory. Some of them arrived at hospitals following overdoses, but in other cases, family members brought in patients who became confused or stopped being able to recognize their relatives or recall basic facts. Some of the patients also struggled with disorientation, attention, and executive function.

In addition to showing the clinical symptoms of amnesia, brain imaging showed a significant reduction in blood flow to the hippocampus, a part of the brain involved in memory, learning, and emotion.

There are only a few case reports in the medical literature of a similar combination of clinical and imaging results, which were a result of cocaine use, influenza, or carbon monoxide poisoning. There was only one case of blood being cut off to the hippocampus as a result of heroin use, from France in 2013.

DeMaria said officials are concerned that increased exposure to synthetic opioids like fentanyl and synthetic marijuana could be playing a role in the recently identified cases. Twelve of the patients had a history of opioid use, and many patients either had a history of using other drugs — including cocaine and benzodiazepines — or tested positive for them.

“The best thing that could happen is, well, no one else has seen this,” he said. But “considering 14 cases in four years, we’re worried we’re going to find more cases.”

The new report appeared in the Morbidity and Mortality Weekly Report, which is published by the Centers for Disease Control and Prevention.

The researchers did not have follow-up data on all the patients, but one 19-year-old man recovered his short-term memory within five months, while one 33-year-old woman still had moderate short-term memory loss more than a year later. One 22-year-old man still had attention and processing problems almost two years later.

DeMaria said he and his colleagues had considered whether the memory loss might be a consequence of an overdose, which depresses breathing and means less oxygen gets to the brain. But he said that even though clinicians saw some wider damage on the brain imaging, the effect was so focused in the hippocampus that something beyond an overdose was probably occurring.

But other researchers not involved with the report said they guessed the amnesia could still have been caused by an overdose.

“I don’t really know if there’s any other plausible explanation,” said Dr. Gary Franklin, a research professor at the University of Washington and fellow of the American Academy of Neurology.

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Still, Franklin called the report both shocking for detailing how some people were dealing with memory issues years later and, at the same time, not all that surprising. Researchers are uncovering new ways opioid use can harm someone, and this finding might just be the latest addition.

Franklin also said the report suggested that it was worth assessing people who recover or are revived from an overdose for damage to their brains.

“This would prompt me to want to study that,” he said.

By publishing the case reports, officials said they hoped that more clinicians will be on the lookout for cases.

“That’s why we want to bring this to people’s attention,” DeMaria said. “Maybe this isn’t an outbreak of a new syndrome, but we won’t know that until people start looking at this more widely and start looking for this earlier in the presentation.”

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