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

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.

Substance use moderates relationships between apolipoprotein E genotype, hepatitis C, cognition, and depression in Miami Adult Studies on HIV (MASH) participants

The impact of APOE on HIV and HCV disease course, cognition, and memory has been understudied in minoritized populations. This study examined whether scores on cognition and depression measures differed by APOE ε4 carrier status while considering HCV and HIV seropositivity and whether these measures were moderated by substance use. A retrospective analysis examined cognitive and psychological data from participants (n = 493) in the Miami Adult Studies on HIV (MASH) cohort. APOE genotyping was performed on banked blood samples. Multiple linear regression was employed to examine differences across participants living with and without HIV and/or HCV and by APOE ε4 genotype. APOE ε4 carriers living with HCV who used cannabis had higher depression scores than non-ε4 carriers, while nonusers had fewer depressive symptoms. APOE ε4 carriers living with HCV had better cognition scores after adjusting for cocaine, opiate, and cannabis use than non-ε4 carriers. Scores on cognitive and depression measures did not differ between APOE ε4 carriers and non-ε4 carriers in participants living with HIV, and substance use did not moderate this relationship. This study was the first of its kind to examine substance use as a moderator for cognition and depression among individuals with HIV and/or HCV stratified by APOE genotype. Findings support further research evaluating the frequency and duration of 1) domains of cognitive functioning impacted by APOE genotype relevant to substance use and 2) the influence of substance use on cognitive and depressive outcomes among adults living with HIV and HCV, HIV, or HCV.

Collateral Damage: Neurological Correlates of Non-Fatal Overdose in the Era of Fentanyl-Xylazine

Non-fatal opioid overdoses are associated with significant morbidity. Hypoxic brain injury caused by opioid-induced respiratory depression is a key mechanism of such morbidity. For example, reports describe an amnestic syndrome in opioid users associated with acute injury to the hippocampus, a brain region that is highly susceptible to hypoxic injury. In our recent study we investigated the effects of non-fatal opioid overdose on the hippocampal volume in a well-characterized sample of opioid use disorder (OUD) patients with a history of overdose (OD) compared to those with no prior overdose (NOD). Using structural magnetic resonance imaging (MRI) and voxel-based morphometry, we observed lower hippocampal volume in patients with a history OD than in the NOD group. These findings support an association between non-fatal opioid overdose and hippocampal injury, which we hypothesize contributes to recently reported cases of OUD related amnestic syndrome. Here we review our study findings and the potential pathophysiological mechanisms underlying the acute and delayed hippocampal injury in nonfatal opioid overdose. We also discuss the implications for the risk of overdose and brain injury with the increased prevalence of fentanyl and xylazine contamination of the illicit opioid supply. Lastly, we highlight considerations for clinical management of the underappreciated neurological injury and cognitive dysfunction in OUD patients.

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.

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.

A pilot study investigating cognitive impairment associated with opioid overdose

BACKGROUND

In 2021, while overdose (OD) deaths were at the highest in recorded history, it is estimated that >80% of ODs do not result in a fatality. While several case studies have indicated that opioid-related ODs can result in cognitive impairment, the possible association has not yet been systematically investigated.

METHODS

78 participants with a history of OUD who reported experiencing an OD in the past year (n=35) or denied a lifetime history of OD (n=43) completed this study. Participants completed cognitive assessments including the Test of Premorbid Functioning (TOPF) and the NIH Toolbox Cognition Battery (NIHTB-CB). Comparisons were made between those who experienced an opioid-related OD in the past year versus those who denied a lifetime OD history while controlling for factors including age, premorbid functioning, and number of prior ODs.

RESULTS

When comparing those who experienced an opioid-related OD within the past year to those without a history of OD, uncorrected standard scores were generally comparable; however, differences emerged in the multivariable model. Specifically, compared to those without a history of OD, those who experienced a past year OD evidenced significantly lower total cognition composite scores (coef. = -7.112; P=0.004), lower crystalized cognition composite scores (coef. = -4.194; P=0.009), and lower fluid cognition composite scores (coef. = -7.879; P=0.031).

CONCLUSIONS

Findings revealed that opioid-related ODs may be associated with, or contribute to, reduced cognition. Extent of the impairment appears contingent upon individuals' premorbid intellectual functioning and the cumulative number of past ODs. While statistically significant, clinical significance may be limited given that performance differences (∼4 - 8 points) were not particularly robust. More rigorous investigation is warranted, and future studies must also account for the many other variables possibly contributing to cognitive impairment.

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

A 31-year-old male with a history significant for obesity, attention deficit hyperactivity disorder, methamphetamine use, and IV drug use was evaluated for unexplained global amnesia greater than 24 h. The patient had been in recovery for opioid use disorder for about a year, but he relapsed on IV fentanyl in the week prior to presentation. On exam, he was alert and fully oriented but had no spontaneous recall of three objects after five minutes. General medical and neurological examinations were otherwise unrevealing. Urine fentanyl and norfentanyl were positive. CT and MRI imaging demonstrated isolated bilateral hippocampal injury. Given the totality of his presentation and the contributing variables, his medical team considered this to be a case of the newly characterized opioid-associated amnestic syndrome (OAS). This case is significant because of the relative absence of potentially confounding variables on presentation, including antecedent cardiorespiratory failure. Further reporting of these cases may have implications for understanding opioid toxicity and clarifying the functional role of the hippocampus.

Neurocognitive impairments and brain abnormalities resulting from opioid-related overdoses: A systematic review

BACKGROUND

Non-fatal opioid-related overdoses have increased significantly over the past two decades and there have been increasing reports of brain injuries and/or neurocognitive impairments following overdose events. Limited preclinical research suggests that opioid overdoses may cause brain injury; however, little is known about such injuries in humans. The purpose this systematic review is to summarize existing studies on neurocognitive impairments and/or brain abnormalities associated with an opioid-related overdose in humans.

METHODS

PubMed, Web of Science, Ovid MEDLINE and PsyINFO were searched, without year restrictions, and identified 3099 articles. An additional 24 articles were identified by reviewing references. Articles were included if they were published in English, reported study findings in humans, included individuals 18 years of age or older, and reported an objective measure of neurocognitive impairments and/or brain abnormalities resulting from an opioid-related overdose. Six domains of bias (selection, performance, attrition, detection (two dimensions) and reporting were evaluated and themes were summarized.

RESULTS

Seventy-nine journal articles, published between 1973-2020, were included in the review. More than half of the articles were case reports (n = 44) and there were 11 cohort studies, 18 case series, and 6 case-control studies. All of the studies were categorized as at-risk of bias, few controlled for confounding factors, and methodological differences made direct comparisons difficult. Less than half of the studies reported toxicology results confirming an opioid-related overdose; 64.6 % reported brain MRI results and 27.8 % reported results of neuropsychological testing. Only two studies had within subject comparative data to document changes in the brain possibly associated with an overdose. Despite these limitations, existing publications suggest that brain injuries and neurocognitive impairments are associated with opioid overdose. Additional research is needed to establish the incidence of overdose-related brain injuries and the potential impact on functioning, as well as engagement in treatment of substance use disorders.

CONCLUSIONS

Respiratory depression is a defining characteristic of opioid overdose and prolonged cerebral hypoxia may cause brain injuries and/or neurocognitive impairments. The onset, characteristics, and duration of such injuries is variable and additional research is needed to understand their clinical implications.

Complete Bilateral Hippocampal Diffusion Restriction and Reversible Amnesia Following Opiate, Cocaine, and Benzodiazepine Abuse

The hippocampus is a crucial component of the circuits involved in memory formation and recall. Bilateral hippocampal lesions can lead to profound anterograde amnesia. As a highly vascularized structure, the hippocampus is susceptible to ischemia from hypoxic and toxic insults. Infarction of bilateral hippocampi as a result of cocaine use, while rare, is well described in the literature. Combined opiate and stimulant abuse also cause dysfunction of this structure. We present a case of complete bilateral hippocampal diffusion restriction and anterograde amnesia after heroin, cocaine, and benzodiazepine abuse, consistent with opioid-associated amnestic syndrome, as well as a remarkable resolution of amnesia months later.

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.