We have characterized 27 cases of leukoencephalopathy associated with 'chasing the dragon'. This is the largest number of cases reported in North America which are temporally and geographically defined. Although an etiologic agent has not been identified, we have a better understanding of the population at risk. The age, sex and ethnicity of our cases are consistent with the demographic profiles in other published reports. Forty-one percent of BC cases were Asian; this preponderance, also found in other studies, is likely representative of persons who 'chase the dragon' .
Identification of two heterosexual case-couples suggests that the risk factors for leukoencephalopathy are more likely to be substance related rather than due to genetic predisposition. The distribution of the cases in place and time suggests a common intermittent exposure. Substances added to the heroin may be an inert 'cutting agent' such as caffeine, lactose or mannitol to increase the volume and hence profit, or an 'adulterant', which is added for its pharmacological effect . The dial-a-dope delivery system identified by some cases may involve additional persons in the supply and delivery chain (i.e., from the dealer to the deliverer) and increase the risk of contaminants being added, either for profit or to retain some drug for personal use. It is unlikely that the contaminant is added to cause intentional harm as it is in the best interest of the dealer to maintain his/her client base.
According to a recent report from the UN Office of the Drug Commission, 96% of heroin seizures (2002-2007) in the US originated from Mexico and Columbia; whereas 98% of heroin seized in Canada originated from Southwest Asia . Although the source of heroin differs between Canada and US, and the epidemiology and prevalence of 'chasing the dragon' in BC is poorly understood, the incidence and risk of the resultant leukoencephalopathy is clearly low. We believe this indicates the contaminant is likely added close to the final delivery stage, rather than at the original source. However there is likely under-reporting as physicians are required to actively report the condition to public health, some cases may have been mild and spontaneously recovered and others attributed to other etiologies.
The purity of street heroin in BC, determined by Health Canada, Drug Analysis Service, has increased from 5-10% in the 1970's, to greater than 60% . However, heroin used for smoking is usually 30% to 40% pure as higher grade cuts char too quickly for effective smoking. Heroin is also reported to be increasingly available in the base form which is not amenable for injection . Smoking heroin in North America was becoming established prior to the knowledge of the risks of HIV associated with injecting . Gossop et al found that chasing the dragon was a well-established method of using heroin in certain populations, not merely a pre-injection phase of heroin addiction . Therefore, drug availability, attitudes to using needles, stigma and the potential of disease transmission related to injection drug use may have led to increased smoking rather than injection of heroin. This illustrates the potential for further cases to occur.
One case with a single brief exposure to inhaling heroin pyrolysate required outpatient support only. This finding was similar to a case report in the literature of a patient with an isolated exposure who had a complete recovery, and is consistent with a dose-response relationship [3, 12]. Clarity of quantity and purity of heroin used by cases would allow a better understanding of a dose-response relationship.
Reported clusters of leukoencephalopathy have been associated with smoking heroin. However isolated cases of leukoencephalopathy associated with using heroin and heroin and cocaine intravenously [30–32], and one case of leukoencephalopathy associated with heroin ingestion occurring in a 2 year old child have been reported . The development of disease associated with other routes of administration highlights the lack of knowledge about the etiological agent and the importance of determining its identity.
The etiology of heroin-related toxic leukoencephalopathy requires further research and public health involvement. The severity of the outcome and lack of curative treatment highlights the importance of future investigations. Current therapy with coenzyme Q and vitamin supplements is anecdotal only . Previous literature has been mostly published in neurology and radiology journals as clinical case reports; isolated cases make it difficult to determine risk factors for this condition. Research into the prevalence of 'chasing the dragon' will help determine the potential risk for further outbreaks and may indicate a need to modify both educational, treatment and support services for this group of heroin users. Although a specific etiology has not been identified, a toxic agent added to the heroin, or a combustion by-product, remain the leading theories [6, 21, 22].
Limitations of our study include incomplete case and drug information. This may be related to the inability of cases to communicate at presentation and the rapid decline in mental state of some. Also, the illicit nature of drug use may cause concerns about sharing information regarding other drug users or the source of heroin. Family members may have little prior knowledge of the case's drug use, limiting the information provided through collateral history. The delay between heroin use and symptom onset also reduces the likelihood that implicated heroin is available for testing.
Recognizing the difficulties inherent in studying such a sporadically occurring condition, a serious effort to determine etiology may require both reactive and prospective approaches. Collaboration with public health, health professionals, law enforcement and persons who use illegal drugs, would facilitate the early identification of cases to enable timely and complete follow-up including obtaining heroin samples. A pre-arranged process for transporting and testing implicated heroin samples may allow identification of the contaminant and therefore prevent further cases. Purity and contaminant sampling programs for street drugs could also be considered. It is therefore important to ensure key stakeholders are aware of these findings and the association of leukoencephalopathy and heroin smoking.