We present a patient with acute onset amnesia secondary to illicit substance use, found to have reversible hippocampal abnormalities on MRI.

Acute amnesia in young patients is rare and often nonphysiologic. However, there have been case series of patients with amnesia and supporting MRI findings of hippocampal injury. One such series attributed the findings to illicit substance abuse, and patient outcomes varied. 

A 21 year-old male with history of bipolar depression and substance abuse presented with sudden onset of amnesia, mixed retrograde and anterograde. Computerized Tomography (CT) of head and blood work were unrevealing. Brain magnetic resonance imaging (MRI) demonstrated symmetric non-enhancing T2/FLAIR signal abnormality and restricted diffusion limited to the bilateral hippocampi.  Family denied any seizure activity, and electroencephalography was normal. Cerebrospinal fluid studies were unremarkable. Urine drug screen was positive for cannabinoids and benzodiazepines. The patient admitted to a history of benzodiazepine abuse, and after brief remission, used unprescribed benzodiazepines the night prior to admission. The patient was discharged with outpatient cognitive therapy.  At four week follow up, memory formation fully returned and MRI findings had normalized. 

In young patients with acute onset amnesia, brain MRI and toxicology screening should be pursued. There are several published cases of bilateral hippocampal injury following substance abuse, with varied degrees of recovery. Treatment is supportive, and involves ruling out other potential causes (infectious, electrographic, anoxic). Etiology is unknown and prognosis varies.