the main active ingredient in various oral pain relief medications. High doses of opiates such as oxycodone can lead to leukoencephalopathy. The activity of various opioid and nociceptive receptors appear to play a role in the disease; however, the exact mechanism remains unknown. Metronidazole, an antibiotic used to treat anaerobic and protozoal infections, has been known at high doses to produce neurologic symptoms associated with toxic leukoencephalopathy. Other Toxic leukoencephalopathy may also result from carbon monoxide poisoning, ingestion of methanol, ingestion of ethylene, toluene toxicity, ethanol poisoning, ingestion of methylenedioxymethamphetamine (MDMA or "ecstasy"), or ingestion of paradichlorobenzene, which is a toxic agent in mothballs. Diagnosis Due to advances in MRI, this neurological disorder has been characterized more successfully in more recent years. MRI can aid in the detection of injured brain tissue; however, the severity and extent of the damage demonstrated by imaging does not always reflect patient clinical status. Toxic leukoencephalopathy encompasses the degeneration of white matter tracts devoted to higher cerebral function; however, white matter can appear normal until the disease has progressed more intensely. Toxic leukoencephalopathy-related damage to central nervous system (CNS) white matter, typically of the periventricular nucleus, and other structures in the brain is often bilateral and symmetric. Heroin-induced leukoencephalopathy often involves damage to cerebellar white matter, posterior cerebral white matter, posterior limb of internal capsule, and cerebellar peduncles. The occipital lobe is typically most affected though the frontal, parietal, and temporal lobes have shown involvement as well. Other toxins have been shown to extend damage to other structures of the brain, including the hippocampus, dorsal medulla, and brainstem. Treatment With such a wide array of causes and unclear understanding of the pathophysiology, there is no known cure or treatment for the disease. In some cases of leukoencephalopathy induced by medications, such as methotrexate and metronidazole, the disease will reduce gradually once the medication is no longer distributed to the patient. Depending on the source of toxicity or pharmacological substance and severity of the white matter damage, many patients can have complete clinical recovery. Coenzyme Q and vitamin supplements, typically vitamin C and vitamin E, and other antioxidant therapies have been suggested to treat heroin-induced leukoencephalopathy patients. However, such treatments have rarely been trialed. See also Leukoencephalopathy References Further reading Neurodegenerative disorders Complications of surgical and medical care Substance-related disorders