Opioid-associated amnestic syndrome (OAS) following cerebellar hippocampal and basal nuclei transient edema with restricted diffusion (CHANTER) syndrome triggered by opioid overdose: A case report

Cerebellar, Hippocampal, and Basal Nuclei Transient Edema with Restricted diffusion (CHANTER) syndrome is a neurological condition characterized by reversible cytotoxic edema involving the cerebellum, hippocampi, and basal nuclei after opioid intoxication. Opioid-associated amnestic syndrome (OAS), in contrast, is clinically characterized by persistent anterograde amnesia accompanied by bilateral hippocampal lesions. We present a 20-year-old patient found in deep coma with suspected opioid overdose. Despite the negative urine opioid screen, typical magnetic resonance (MR) findings led to a diagnosis of CHANTER syndrome. The patient's neurological status improved dramatically after hemodialysis. However, the patient subsequently developed mild persistent anterograde amnesia with hippocampal atrophy consistent with OAS. This case highlights the importance of early magnetic resonance (MR) diagnosis and hemodialysis in addressing opioid-induced neurotoxicity. Moreover, CHANTER syndrome may represent an acute, widespread manifestation, while OAS may emerge subsequently as a localized amnestic condition, reflecting temporal and spatial progression of the pathology. In addition, frequent overdoses may contribute to frontal lobe dysfunction.