Toxic leukoencephalopathy

Toxic leukoencephalopathy or toxic spongiform leukoencephalopathy is a rare condition that is characterized by progressive damage (-pathy) to white matter (-leuko-) in the brain (-encephalo-), particularly myelin, due to causes such as exposure to drugs of abuse, environmental toxins, or chemotherapeutic drugs. The prevalence of this disease is infrequent and often goes unreported, especially in cases resulting from drug abuse. Magnetic resonance imaging (MRI) is a popular method to study and diagnose the disease. However, even with technological advances, the exact mechanism and underlying pathophysiology of toxic leukoencephalopathy remains unknown and is thought to vary between sources of toxicity. The clinical severity of toxic leukoencephalopathy also varies among patients, exposure time, and concentration and purity of the toxic agent. Some reversibility of the condition has been seen in many cases when the toxic agent is removed.

Various pharmacological agents have been known to cause toxic leukoencephalopathy. The most common causes are substance abuse drugs and chemotherapy; however, the disease has also occurred on the rare occasion as a side effect to certain medications and environmental toxins.

Leukoencephalopathy may result from the inhalation, intravenous injection, or ingestion of substance abuse drugs. However, such occurrences are rare, sporadic, and often go undocumented. Leukoencephalopathy caused by inhalation of heroin, also known as "chasing the dragon" syndrome, is one of the most studied of these rare occurrences and has even been recognized for over twenty five years.

It is believed by some researchers that heroin-induced leukoencephalopathy may be caused by a contaminant, or “cutting agent,” in the heroin. However, no such agent has been identified; and indeed, toxic leukoencephalopathy has been observed as a result of intoxication with contaminant-free opiates. Cases include a 65-year-old woman who had mistakenly been taking three times the dose of methadone that had been prescribed for pain management, and a young girl intoxicated with pure morphine sulphate tablets.

Other drugs that have been associated with toxic leukoencephalopathy in much more rare occurrences include psychoactive drug 2C-E ("Europa"),oxycodone,cocaine, and methadone. The dose-response relationship for these substances remains unclear.

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