Acute Amnestic Syndrome Associated with Fentanyl Overdose

Histopathologic correlates of opioid-associated injury in CHANTER syndrome: first report of a post-mortem examination

Opioid-associated brain injury may involve selective regions, including the hippocampi alone, globi pallidi, and cerebellar hemispheres. Opioid-associated amnestic syndrome, for example, is one clinical correlate of hippocampal injury as manifest by MRI abnormality. When all three regions are involved in what may be a more fulminant injury, the syndrome is termed "cerebellar, hippocampal, and basal nuclei transient edema with restricted diffusion (CHANTER)", initially described in 2019. Until now, to our knowledge, there have been no histopathologic correlates to the imaging findings specifically in CHANTER syndrome. Here, for the first time, we present histopathologic findings of the post-mortem brain from a patient who died from complications of CHANTER syndrome following fentanyl intoxication. These observations included microhemorrhage, reactive and necrotic vasculature, eosinophilic neuronal necrosis, axonal swelling and spheroids, and frank infarction. The findings support previous experimental models implicating both hypoxic-ischemic and cytotoxic mechanisms in the tissue damage associated with CHANTER syndrome, though further work is needed to better characterize the exact cellular pathways involved to develop targeted treatments.

Opioid-Associated Nervous System Injuries

With the rise of the opioid epidemic, the practicing neurologist must recognize the patterns of a growing number of opioid-associated neurological injuries. This is in addition to the classic toxidrome of miosis, altered mental status, and respiratory depression, which must never be overlooked, as it is reversible and potentially lifesaving. Several other idiosyncratic syndromes due to opioid-related nervous system insults are defined by their characteristic imaging findings and portend variable functional recovery. Opioid toxicity can not only lead to brain injury, but also spinal cord and, rarely, peripheral nerve injury. As several newer synthetic opioids are undetectable by most assays, a low threshold to suspect opioid exposure must be maintained.

Is there a relationship between opioid use and transient global amnesia?

BACKGROUND AND PURPOSE

Opioid-associated amnestic syndrome (OAS) and transient global amnesia (TGA) are conditions with clinical overlap. We therefore sought to determine whether opioid use might be associated with TGA.

METHODS

Data from the Massachusetts Department of Public Health Syndromic Surveillance program were queried to ascertain the frequency of opioid use among emergency department (ED) encounters for TGA compared to that for all other ED visits between January 2019 and June 2023.

RESULTS

A total of 13,188,630 ED visits were identified during the study period. Of 1417 visits for TGA, one visit met the exposure definition for opioid use. There were 13,187,213 visits for other indications, 57,638 of which were considered opioid-exposed. The odds ratio for the relationship between opioid use and TGA was 0.16 (95% confidence interval 0.02, 1.14).

CONCLUSION

Despite the clinical overlap between OAS and TGA, surveillance data from ED visits in Massachusetts do not suggest that opioid use is a risk factor for TGA, indicating that OAS and TGA are distinct entities.

An imaging review of the hippocampus and its common pathologies

The hippocampus is a complex structure located in the mesial temporal lobe that plays a critical role in cognitive and memory-related processes. The hippocampal formation consists of the dentate gyrus, hippocampus proper, and subiculum, and its importance in the neural circuitry makes it a key anatomic structure to evaluate in neuroimaging studies. Advancements in imaging techniques now allow detailed assessment of hippocampus internal architecture and signal features that has improved identification and characterization of hippocampal abnormalities. This review aims to summarize the neuroimaging features of the hippocampus and its common pathologies. It provides an overview of the hippocampal anatomy on magnetic resonance imaging and discusses how various imaging techniques can be used to assess the hippocampus. The review explores neuroimaging findings related to hippocampal variants (incomplete hippocampal inversion, sulcal remnant and choroidal fissure cysts), and pathologies of neoplastic (astrocytoma and glioma, ganglioglioma, dysembryoplastic neuroepithelial tumor, multinodular and vacuolating neuronal tumor, and metastasis), epileptic (mesial temporal sclerosis and focal cortical dysplasia), neurodegenerative (Alzheimer's disease, progressive primary aphasia, and frontotemporal dementia), infectious (Herpes simplex virus and limbic encephalitis), vascular (ischemic stroke, arteriovenous malformation, and cerebral cavernous malformations), and toxic-metabolic (transient global amnesia and opioid-associated amnestic syndrome) etiologies.

Cerebellar, hippocampal, and basal nuclei transient edema with restricted diffusion (CHANTER) syndrome in the setting of opioid and phencyclidine use

Cerebellar, hippocampal, and basal nuclei transient edema with restricted diffusion (CHANTER) syndrome is a constellation of specific imaging findings characterized by cytotoxic edema in the bilateral hippocampi, cerebellar cortices, and basal ganglia in patients presenting with altered mental status in the setting of substance intoxication. Previous case reports have demonstrated a strong correlation between CHANTER syndrome and polysubstance abuse, particularly with opioid intoxication. The patient we present in this case was found unresponsive following opioid use and demonstrated a constellation of findings on initial and follow-up imaging, consistent with CHANTER syndrome. While cases of irreversible brain damage or death during hospitalization have been reported in the literature, our patient demonstrated near-full recovery a few days after admission to the hospital. We aim to highlight the presentation and progression of CHANTER syndrome and alert clinicians and radiologists to include this entity in their diagnostic checklist for patients with polysubstance abuse and altered mental status.

Hippocampal volume loss in individuals with a history of non-fatal opioid overdose

Incidence of opioid-related overdoses in the United States has increased dramatically over the past two decades. Despite public emphasis on overdose fatalities, most overdose cases are not fatal. Although there are case reports of amnestic syndromes and acute injury to the hippocampus following non-fatal opioid overdose, the effects of such overdoses on brain structure are poorly understood. Here, we investigated the neuroanatomical correlates of non-fatal opioid overdoses by comparing hippocampal volume in opioid use disorder (OUD) patients who had experienced an opioid overdose (OD; N = 17) with those who had not (NOD; N = 32). Voxel-based morphometry showed lower hippocampal volume in the OD group than in the NOD group, which on post hoc analysis was evident in the left but not the right hippocampus. These findings strengthen the evidence that hippocampal injury is associated with non-fatal opioid overdose, which is hypothesized to underlie overdose-related amnestic syndrome.

Longitudinal Imaging in a Patient With Opioid-associated Amnestic Syndrome

Since 2012, individuals with a history of opioid misuse have infrequently been observed to develop a sudden-onset amnestic syndrome associated with bilateral hippocampal-restricted diffusion on MRI. Follow-up imaging of this opioid-associated amnestic syndrome (OAS) has revealed persistent hippocampal abnormalities. Given these observations, as well as neuropathological studies demonstrating excessive tau deposition in the hippocampi and other brain regions of individuals with opioid misuse, we describe longitudinal imaging of a patient with a history of OAS from presentation through 53 months later, when tau positron emission tomography (PET) was performed. Our patient was a 21-year-old woman with a history of attention-deficit hyperactivity disorder and substance use disorder, including opioids (intravenous heroin), who was hospitalized for acute-onset, dense anterograde amnesia. Her urine toxicology screen was positive for opiates. On presentation, her brain MRI showed restricted diffusion as well as T2 and fluid-attenuated inversion recovery (FLAIR) hyperintensity of the hippocampi and globi pallidi. On day 3, magnetic resonance spectroscopy of a right hippocampal region of interest showed a mild reduction of N-acetyl aspartate/creatine, slight elevation of choline/creatine, and the appearance of lactate/lipid and glutamate/glutamine peaks. At 4.5 months, there was resolution of restricted diffusion on MRI, although a minimal anterior T2 and FLAIR hyperintense signal in the right hippocampus persisted. However, by 53 months, when mild memory loss was reported, the hippocampi appeared normal on MRI, and [ 18 F]T807 (tau) PET showed no uptake suggestive of tau deposition. This case report supports the investigation into the hypothesis that OAS may follow a trajectory of reversible metabolic injury.

Hippocampal and Cerebellar Involvement in Opioid-Associated Amnestic Syndrome: A Unique Case Report

We present a case of opioid-associated amnestic syndrome (OAS) in a 46-year-old female with persistent acute anterograde amnesia and biochemically confirmed with fentanyl use. The brain Magnetic Resonance Imaging (MRI) examination demonstrated symmetric restricted diffusion and T2/fluid-attenuated inversion recovery (FLAIR) hyperintensities in the hippocampi and cerebellum. While cases of cerebellar findings in OAS are rare in the literature, this is a unique case with corresponding images that demonstrate cerebellar involvement in addition to the more common hippocampal finding.

Association between toxic drug events and encephalopathy in British Columbia, Canada: a cross-sectional analysis

BACKGROUND

Encephalopathy can occur from a non-fatal toxic drug event (overdose) which results in a partial or complete loss of oxygen to the brain, or due to long-term substance use issues. It can be categorized as a non-traumatic acquired brain injury or toxic encephalopathy. In the context of the drug toxicity crisis in British Columbia (BC), Canada, measuring the co-occurrence of encephalopathy and drug toxicity is challenging due to lack of standardized screening. We aimed to estimate the prevalence of encephalopathy among people who experienced a toxic drug event and examine the association between toxic drug events and encephalopathy.

METHODS

Using a 20% random sample of BC residents from administrative health data, we conducted a cross-sectional analysis. Toxic drug events were identified using the BC Provincial Overdose Cohort definition and encephalopathy was identified using ICD codes from hospitalization, emergency department, and primary care records between January 1st 2015 and December 31st 2019. Unadjusted and adjusted log-binomial regression models were employed to estimate the risk of encephalopathy among people who had a toxic drug event compared to people who did not experience a toxic drug event.

RESULTS

Among people with encephalopathy, 14.6% (n = 54) had one or more drug toxicity events between 2015 and 2019. After adjusting for sex, age, and mental illness, people who experienced drug toxicity were 15.3 times (95% CI = 11.3, 20.7) more likely to have encephalopathy compared to people who did not experience a drug toxicity event. People who were 40 years and older, male, and had a mental illness were at increased risk of encephalopathy.

CONCLUSIONS

There is a need for collaboration between community members, health care providers, and key stakeholders to develop a standardized approach to define, screen, and detect neurocognitive injury related to drug toxicity.

Fentanyl Induces Novel Conditioned Place Preference in Adult Zebrafish, Disrupts Neurotransmitter Homeostasis, and Triggers Behavioral Changes

Abuse of new psychoactive substances increases risk of addiction, which can lead to serious brain disorders. Fentanyl is a synthetic opioid commonly used in clinical practice, and behavioral changes resulting from fentanyl addiction have rarely been studied with zebrafish models. In this study, we evaluated the rewarding effects of intraperitoneal injections of fentanyl at concentrations of 10, 100, and 1000 mg/L on the group shoaling behavior in adult zebrafish. Additional behavioral tests on individual zebrafish, including novel tank, novel object exploration, mirror attack, social preference, and T-maze memory, were utilized to evaluate fentanyl-induced neuro-behavioral toxicity. The high doses of 1000 mg/L fentanyl produced significant reward effects in zebrafish and altered the neuro-behavioral profiles: reduced cohesion in shoaling behavior, decreased anxiety levels, reduced exploratory behavior, increased aggression behavior, affected social preference, and suppressed memory in an appetitive associative learning task. Behavioral changes in zebrafish were shown to be associated with altered neurotransmitters, such as elevated glutamine (Gln), gamma-aminobutyric acid (GABA), dopamine hydrochloride (DA), and 5-hydroxytryptamine (5-HT). This study identified potential fentanyl-induced neurotoxicity through multiple neurobehavioral assessments, which provided a method for assessing risk of addiction to new psychoactive substances.

Neuroimaging Findings in CHANTER Syndrome: A Case Series

Recently, a distinct clinicoradiologic entity involving cerebellar, hippocampal, and basal nuclei transient edema with restricted diffusion (CHANTER) on MR imaging was identified. Patients present in an unresponsive state following exposure to drugs of abuse. Very little information exists regarding this entity, particularly in the radiology literature. We identify and describe 3 patients at our institution with similar clinical and radiographic findings. Multifocal restricted diffusion in the brain is typically associated with poor outcomes. By contrast, CHANTER involves intraventricular obstructive hydrocephalus that, when treated, can lead to substantial recovery. This novel syndrome should be on the differential in patients who present in an unresponsive state after recent opioid use in the context of the above imaging findings. Additional diagnoses on the differential can include ischemic stroke, hypoxic-ischemic encephalopathy, "chasing the dragon," leukoencephalopathy, opioid-associated amnestic syndrome, and pediatric opioid-use-associated neurotoxicity with cerebellar edema.

Application of an Existing Syndromic Surveillance System to Quantify Possible Cases of Opioid-associated Amnestic Syndrome in Massachusetts

OBJECTIVES

In recent years, an opioid-associated amnestic syndrome (OAS) was identified in Massachusetts through elicited reporting by health care providers (traditional surveillance, TS). Whether OAS occurs more frequently and with a wider spatiotemporal distribution in Massachusetts remains unclear. We compared the frequency and spatiotemporal characteristics of emergency department (ED) visits for possible OAS (pOAS) using a pre-existing syndromic surveillance system (SyS) with OAS cases captured through TS.

METHODS

SyS was queried for Massachusetts ED visits in 15- to 55-year-olds with a chief complaint text and discharge codes for memory loss in association with codes for opioid use (pOAS). SyS data were extracted for 2016-2020, whereas TS was conducted for 2012-2018. Cases identified by SyS and TS were stratified by demographic and spatiotemporal variables.

RESULTS

TS ascertained 22 reported cases of OAS (18 males) between 2012 and 2018, ranging from 0 to 5 annually. No identified OAS patients presented between January and March or in western Massachusetts. Between 2016 and 2020, SyS identified 82 ED visits (49 males) with pOAS, ranging from 13 to 22 per year. Over the 5-year period, at least 2 ED visits for pOAS occurred during each month of the year (24 total during January, February, or March) and at least 1 visit occurred in each county except 2, with the second largest number (11) in Berkshire County (at the western border of Massachusetts), where no cases were ascertained through TS.

CONCLUSIONS

Although OAS is a relatively rare condition, use of SyS in Massachusetts suggests a broader and more frequent spatiotemporal distribution than previously indicated from TS.

Opioid-Associated Amnestic Syndrome

Opioid-associated amnestic syndrome (OAS) is a relatively new condition that is associated with opioid abuse and has increased in prevalence since the notable rise in opioid-related deaths and opioid-related hospitalizations of the opioid crisis. Patients often present with acute anterograde amnesia and current opioid abuse, most commonly fentanyl. OAS is frequently diagnosed when other potentially infectious or metabolic conditions such as encephalitis and seizures are ruled out, as these conditions can also present similarly to OAS. This case highlights the signs, symptoms, and hallmark characteristics of OAS, including bilateral hippocampal edema and anterograde amnesia.

Neurotoxicology Syndromes Associated with Drugs of Abuse

Substance use disorders-and their associated neurologic complications-are frequently encountered by neurologists as well as emergency room physicians, internists, psychiatrists, and medical intensivists. Prominent neurologic sequelae of drug abuse, such as seizure and stroke, are common and often result in patients receiving medical attention. However, less overt neurologic manifestations, such as dysautonomia and perceptual disturbances, may be initially misattributed to primary medical or psychiatric illness, respectively. This article focuses on the epidemiology, pharmacology, and complications associated with commonly used recreational drugs, including opioids, alcohol, marijuana, cocaine, and hallucinogens.

Opioid-associated amnestic syndrome: Description of the syndrome and validation of a proposed definition

OBJECTIVE

An opioid-associated amnestic syndrome (OAS) characterized by acute onset memory loss and bilateral hippocampal signal abnormalities on brain imaging in the setting of a history of opioid use, most notably fentanyl, has been reported. To date, however, there is no case definition to assist neurologists and other clinicians in identifying this syndrome. A multi-disciplinary collaboration of physicians, including neurologists, propose diagnostic criteria for OAS using cases that have been published in the medical literature or presented at conferences.

METHODS

Cases were classified as confirmed, probable, or possible based on brain imaging findings and history or analytical testing supporting opioid use. Published articles and presentations were identified by discussion with public health authorities and a systematic search of PubMed. Included were articles, abstracts or posters through November 2019 that presented case reports or case series of a new-onset amnestic syndrome associated with bilateral hippocampal injury on imaging and/or prior opioid or other substance use. The percentages of cases that would meet confirmed, probable, or possible criteria were calculated.

RESULTS

Twenty-three publications from all sources met criteria for inclusion, accounting for 40 unique cases. Based on the case definition of OAS, 50% (20/40) were confirmed, 25% (10/40) were probable and 25% (10/40) were possible.

CONCLUSION

The development of a validated, formal case definition for OAS can assist neurologists and other clinicians in evaluating patients with amnesia and a history of opioid use.

Cerebellar Hippocampal and Basal Nuclei Transient Edema with Restricted diffusion (CHANTER) Syndrome

Background

Abnormal restricted diffusion on magnetic resonance imaging is often associated with ischemic stroke or anoxic injury, but other conditions can present similarly. We present six cases of an unusual but consistent pattern of restricted diffusion in bilateral hippocampi and cerebellar cortices. This pattern of injury is distinct from typical imaging findings in ischemic, anoxic, or toxic injury, suggesting it may represent an under-recognized clinicoradiographic syndrome. Despite initial presentation with stupor or coma in the context of obstructive hydrocephalus, patients may have acceptable outcomes if offered early intervention.

Methods

We identified an ad hoc series of patients at our two institutions between years 2014 and 2017 who presented to the neurocritical care unit with severe, otherwise unexplained cerebellar edema and retrospectively identified several commonalities in history, presentation, and imaging.

Results

Between two institutions, we identified six patients—ages 33–59 years, four male—with similar presentations of decreased level of consciousness in the context of intoxicant exposure, with acute cytotoxic edema of the cerebellar cortex, hippocampi, and aspects of the basal nuclei. All patients presented with severe cerebellar edema which led to obstructive hydrocephalus requiring aggressive medical and/or surgical management. The five patients who survived to discharge demonstrated variable degrees of physical and memory impairment on discharge and at follow-up.

Conclusions

We present findings of a potentially novel syndrome involving a distinct pattern of cerebellar and hippocampal restricted diffusion, with imaging and clinical characteristics distinct from ischemic stroke, hypoxic injury, and known toxidromes and leukoencephalopathies. Given the potential for favorable outcome despite early obstructive hydrocephalus, early identification and treatment of this syndrome are critical.

The rising crisis of illicit fentanyl use, overdose, and potential therapeutic strategies

Fentanyl is a powerful opioid anesthetic and analgesic, the use of which has caused an increasing public health threat in the United States and elsewhere. Fentanyl was initially approved and used for the treatment of moderate to severe pain, especially cancer pain. However, recent years have seen a growing concern that fentanyl and its analogs are widely synthesized in laboratories and adulterated with illicit supplies of heroin, cocaine, methamphetamine, and counterfeit pills, contributing to the exponential growth in the number of drug-related overdose deaths. This review summarizes the recent epidemic and evolution of illicit fentanyl use, its pharmacological mechanisms and side effects, and the potential clinical management and prevention of fentanyl-related overdoses. Because social, economic, and health problems that are related to the use of fentanyl and its analogs are growing, there is an urgent need to implement large-scale safe and effective harm reduction strategies to prevent fentanyl-related overdoses.

A human memory circuit derived from brain lesions causing amnesia

Human memory is thought to depend on a circuit of connected brain regions, but this hypothesis has not been directly tested. We derive a human memory circuit using 53 case reports of strokes causing amnesia and a map of the human connectome (n = 1000). This circuit is reproducible across discovery (n = 27) and replication (n = 26) cohorts and specific to lesions causing amnesia. Its hub is at the junction of the presubiculum and retrosplenial cortex. Connectivity with this single location defines a human brain circuit that incorporates > 95% of lesions causing amnesia. Lesion intersection with this circuit predicts memory scores in two independent datasets (N1 = 97, N2 = 176). This network aligns with neuroimaging correlates of episodic memory, abnormalities in Alzheimer's disease, and brain stimulation sites reported to enhance memory in humans.

ISMP Adverse Drug Reactions: Pheochromocytoma Crisis Induced by Metoclopramide Baclofen Dependence Following High-Dose Therapy Fatal Cardiotoxicity Following High-Dose Cyclophosphamide Acute Anterograde Amnestic Syndrome Induced by Fentanyl Ivermectin-Induced Toxic Epidermal Necrolysis Pembrolizumab-Induced Type 1 Diabetes

The purpose of this feature is to heighten awareness of specific adverse drug reactions (ADRs), discuss methods of prevention, and promote reporting of ADRs to the US Food and Drug Administration's (FDA) MedWatch program (800-FDA-1088). If you have reported an interesting, preventable ADR to MedWatch, please consider sharing the account with our readers. E-mail Dr. Mancano at michael.mancano@temple.edu. Your report will be published anonymously unless otherwise requested. This feature is provided by the Institute for Safe Medication Practices (ISMP) in cooperation with the FDA's MedWatch program and Temple University School of Pharmacy. ISMP is an FDA MedWatch partner.

Commentary. Fentanyl-related death and the underreporting risk

Novel synthetic opioid overdose deaths have been rising largely worldwide as a result of fentanyl adulteration in the illegal drug supply. Interpretation of post mortem analytical results concerning fentanyl can be challenging in particular due to redistribution phenomena. Lacking of resources, infrastructures and expertise to perform forensic toxicological investigation when an unknown drug or complex mixture of drugs is suspected can affect failure in exactly reporting cause in drug related death. Public safety and public health entities are called working together to enhance the timeliness and accuracy of the analytical characterization and toxicology testing of novel synthetic opioids.

Connecting the dots: an association between opioids and acute hippocampal injury

Acute hippocampal injury represents a relatively rare cause of amnesia. Interestingly however, between 2012 and 2017, 18 patients were reported at hospitals in Massachusetts with sudden-onset amnesia in the setting of complete diffusion-weighted hyperintensity of both hippocampi on magnetic resonance imaging. Notably, 17 of the 18 patients tested positive for opioids or had a recorded history of opioid use. This observation suggests an association between opioids and acute hippocampal injury. With particular attention to the Massachusetts cluster and data on fentanyl and its congeners, the epidemiological and pathophysiological evidence that supports this hypothesis is presented, as are potential underlying mechanisms.