This study aimed to conduct a preliminary analysis of the risk of encephalopathy among people who had an illicit drug poisoning in a population-based sample. The prevalence of drug poisoning among people with encephalopathy between January 1st, 2015 and December 31st, 2019 was 15%. After adjusting for demographic and mental illness, we demonstrated that people who experienced an illicit drug poisoning event were 15 times more likely to have encephalopathy than people who did not experience an illicit drug poisoning. These findings highlight the potential long-term health outcomes that persons may experience following drug poisoning, along with the need to develop health care services and outreach programs specifically for people who experience drug poisoning and a neurocognitive injury.
Most studies which examine toxic encephalopathy among people who experienced drug poisonings are clinical case reports (4, 5, 11, 13, 14, 24, 25, 26, 27, 28) suggesting that encephalopathy is an important health concern among this population. Though population level studies that estimate overdose-related encephalopathy are limited (19), and no existing literature attempts to estimate the co-occurrence of toxic encephalopathy and drug poisoning, there are some consistencies between our findings and the available literature. A study by Morrow et al. reported that 3% of patients admitted to hospitals from 2006 to 2015 in BC, Canada for accidental opioid overdose had a record of encephalopathy as a result of an overdose event (19). In the study, overdose is only identified using hospitalization, inpatient, and outpatient records therefore underestimates the number of people who had an illicit drug poisoning event, particularly people who experienced illicit drug poisoning in the community. Older age has also been described as an important factor that affects the severity of recovery from encephalopathy (15, 25). Consistent with the available literature, our study found a high proportion of people with encephalopathy died from drug poisoning within the study timeframe (1, 25).
Though it is not possible to ascertain temporality in the association between overdose and encephalopathy given the cross-sectional nature of our analysis, most of the available literature outlines directionality where overdose leads to encephalopathy. Increasingly, the literature is highlighting the potential health implications of non-fatal overdoses on neuropathology and cognitive health outcomes (29, 30). Diagnosis of encephalopathy is complex as there may be delayed onset of symptoms (6, 14), clinical presentations vary, and there rarely exists a measure of pre-existing neurological function (5, 15). The lack of standardized mechanism to identify drug poisoning-related encephalopathy using clinical or radiological methods (1) suggest that our study may underestimate the prevalence of encephalopathy. There is a need for collaboration between health care providers, experts, and key stakeholders to develop a standardized approach to define, screen, and detect neurocognitive injury among people experiencing drug poisonings. Encephalopathy, particularly if undiagnosed or untreated, can severely affect cognitive capabilities (1, 25), increase the likelihood of subsequent drug poisoning events, and impact social activities and livelihoods. And, may compound existing barriers, such as access to housing, employment, community supports, and increasing experiences of stigma (3). Several studies have outlined significant changes in a person’s level of independence following encephalopathy from a drug poisoning (15, 25), which has important implications for health and long-term care provision. Studies have also described the positive impacts of rehabilitation among people with drug poisoning-related encephalopathy (5, 7, 8, 25), highlighting the importance of screening. There is a need for studies to examine the temporal association between encephalopathy and illicit drug poisonings, and longitudinal analyses to estimate the incidence of encephalopathy among people who experienced drug poisonings.
i. Limitations
Due to the cross-sectional nature of the analysis, we are not able to determine the temporal relationship between encephalopathy and illicit drug poisoning. Though there seems to be a strong association, it is unclear whether people who experienced drug poisoning are at increased risk of encephalopathy or if people with encephalopathy are at increased risk of a drug poisoning event, or both. Measuring encephalopathy using administrative data can be challenging as diagnostic codes likely capture the most severe cases and underestimate the burden of mild to moderate cases, particularly given the lack of screening. The use of ICD codes to examine encephalopathy likely result in low specificity and impacts the ability to identify encephalopathy among the study population. Not every person who experiences a drug poisoning accesses health care, therefore not all drug poisonings, or cases of encephalopathy are reported. Our findings of a high proportion of drug poisoning deaths among people with an encephalopathy diagnostic code could be attributable to an over-representation of severe encephalopathy cases but may also reflect risky drug using behaviours among people who have encephalopathy.