The Cases

In November 2015, a neurologist in the Boston area reported four cases of an uncommon amnestic syndrome involving acute and complete ischemia of both hippocampi, as identified by magnetic resonance imaging (MRI), to the Massachusetts Department of Public Health (MDPH).¹ A subsequent e-mail alert, generated by the Massachusetts Board of Registration in Medicine and sent to relevant medical specialists (including neurologists, neuroradiologists, and emergency physicians), resulted in the identification of 10 additional cases that had occurred during 2012–2016. All 14 patients (mean and median age = 35 years) had been evaluated at hospitals in eastern Massachusetts. Thirteen of the 14 patients underwent routine clinical toxicology screening at the time of initial evaluation; eight tested positive for opioids, two for cocaine, and two for benzodiazepines. Apart from sporadic cases, this combination of clinical and imaging findings has been reported rarely.^2–6 The apparent temporospatial clustering, relatively young age at onset (19–52 years), and associated substance use among these patients should stimulate further case identification to determine whether these observations represent an emerging syndrome related to substance use or other causes (eg, a toxic exposure).

The four patients reported in November 2015 had been evaluated at a single Boston-area medical center during the preceding three years.¹ MRI of the head revealed changes consistent with acute and complete ischemia of both hippocampi in all four patients at the time of initial evaluation. Three of the four patients tested positive for opiates on initial toxicology screening, and the fourth, who was not tested, had a reported history of heroin use. No readily apparent evidence for another established etiology of hippocampal amnesia existed for any of the patients.^7,8 Several previous isolated case reports were associated with cocaine use only, and one case of complete unilateral hippocampal infarction involving heroin inhalation was reported in France in 2013.^{2–4, 9}