Anterograde amnesia and bilateral hippocampus ischemia: is it caused by substance abuse?
January 26, 2017, 11:51 pm
Cluster of an Unusual Amnestic Syndrome — Massachusetts, 2012-2016. Barash JA et al. MMWR Morb Mortal Wkly Rep 2017;66:76-79
Late in 2015 a Boston neurologist reported a cluster of 4 cases of anterograde amnesia associated with MRI evidence of bilateral hippocampal ischemia. After a public health alert was issued an additional 10 cases were identified in the years 2012-2016, using the case definition of: “1) new onset amnesia in the absence of evidence to support a readily apparent cause, and 2) changes consistent with acute and complete ischemia of both hippocampi on MRI at initial assessment.”
Of the 14 identified patients, all had a history consistent with substance abuse or drug screening consistent with such abuse. In 13 of the patients, this history involved opioids. Additional neurological findings in these cases included deficits in attention orientation, and executive functioning. Some of these deficits resolved over time, but several patients had residual impairment at 1-year follow-up.
Authors note that previously reported causes of amnestic syndrome with bilateral complete hippocampal ischemia include cocaine, carbon monoxide, and influenza. They admit that hypoxia-induced hippocampal ischemia is a possibility. Others have speculated that changes in glutamate balance may be responsible.
The authors’ conclusion:
MRI of the head,toxicology screen, and neurologic consultation should be considered in all adults age > 18 years with sudden-onset amnesia, particularly in patients with altered consciousness. Advanced laboratory testing, including testing for synthetic opioids (e.g., fentanyl) and their analogies, as well as extraneous substances not assessed in these reported cases, might further clarify an association with substance use.
The initial 4 cases have been reported previously in the medical literature.