Four cases were initially reported in November 2015, which led to an investigation that increased the number of cases to 10 occurring between 2012 and 2016. Thirteen of the 14 total patients had undergone routine clinical toxicology screening at initial evaluation, of which eight tested positive for opioids, two for cocaine, and two for benzodiazepines. "This cluster of amnestic syndrome associated with bilateral complete hippocampal ischemia is unusual given the absence of a readily identifiable etiology, the temporospatial clustering, relatively young patient age, and extensive substance use among affected persons," the investigators noted. MRI of the head of the four patient cases from November 2015 showed changes consistent with acute and complete ischemia of both hippocampi. “He could not retain any new information,” Lim said. Regarding substance use disorders, 12 of 14 patients had a history of opioid use, and eight tested positive for opiates on routine toxicology screening. CDC Investigating Unusual Amnestic Syndrome Cases 
 
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 Prior to recent reports, the combination of these clinical findings were rare and tied to cocaine use, flu, and poisoning 
 
 The Centers for Disease Control and Prevention (CDC)'s Morbidity and Mortality Weekly Report describes several cases of an unusual amnestic syndrome, involving acute and complete ischemia of both hippocampi, reported to the Massachusetts Department of Public Health (MDPH).
– Since 2012, doctors in Massachusetts have observed a most unusual kind of patient just 14 times—or, 14 times that we know about. It all started with Max Meehan, who was taken to the hospital after his behavior freaked out his family: his memory had suddenly vanished. "The kid was amnestic," neurologist Yuval Zabar says of the then-23-year-old, and what Zabar found when he reviewed an MRI scan of Meehan's brain essentially freaked him out: As BuzzFeed puts it, two bright white orbs where there should have been gray, each "perfectly localized" to both hippocampi, which plays a crucial role in the formation of memories. Zabar had never seen it before, but it wasn't a total anomaly: Doctors in the state have now identified 13 more people who experienced the same white orbs and memory issues, and one of their commonalities, with two exceptions, is opioid use. In Meehan's case, he shot up heroin and collapsed before waking to a seeming inability to form new memories, leaving him in a state that forced him to drop out of college and made it difficult to hold a job. Memory improvements came slowly over two years. "The only thing that seems to parallel" the condition—which has been named CHIAS, for complete hippocampal ischemic amnestic syndrome—"is fentanyl use," says another Massachusetts neurologist. Among the many varied theories: that there was a toxin in the drugs ingested, or that persistent fentanyl use results in severe respiratory issues that may deprive those parts of the brain of oxygen. For now, state public health officials are pushing the mystery forward by branding CHIAS a "reportable disease," meaning the state will have to be alerted to any new cases. Read the full piece.