Toxic leukoencephalopathy
Progressive white matter damage from toxins, drugs, or chemotherapy.
Toxic leukoencephalopathy is a rare condition involving progressive damage to the brain's white matter, particularly myelin, from exposure to substances such as drugs, environmental toxins, or chemotherapeutic agents. Its prevalence is infrequent and often unreported, especially in cases linked to substance use. The exact pathophysiology remains unknown and is thought to vary by toxic source, though some reversibility has been observed upon removal of the agent.
Quick Facts
- Synonym
- Toxic spongiform leukoencephalopathy
Facts from the source article.
Signs and symptoms
Symptoms vary widely depending on the toxic agent, dosage, exposure duration, patient history, and genetics. In cases from substance use or environmental toxins, symptoms typically emerge days to months after exposure. Clinical features range from inattention, forgetfulness, and personality changes to dementia, coma, and death. Common initial signs include confusion, somnolence, generalized seizures, headaches, and vision impairment. Young acute lymphoblastic leukemia patients with methotrexate-induced leukoencephalopathy often appear asymptomatic, whereas substance-induced cases tend to cause more severe damage. Heroin-induced leukoencephalopathy progresses through three stages: first, soft speech, cerebellar ataxia, motor restlessness, and apathy; intermediate stage includes pyramidal tract signs, spastic paresis, myoclonic jerks, and choreoathetoid movements; terminal stage features stretching spasms, akinetic mutism, hypotonic paresis, central pyrexia, and death. Oral methotrexate for arthritis can cause ataxia, dysarthria, and seizures, with long-term cognitive effects unknown. Metronidazole overdose leads to dysarthria, gait disturbance, weakness, and confusion. Some patients recover completely.
Causes
Various pharmacological agents cause toxic leukoencephalopathy, most commonly substance use and chemotherapy, though it can also occur as a rare side effect of certain medications or environmental toxins. Inhalation, intravenous injection, or ingestion of addictive substances may lead to the condition, but such occurrences are rare, sporadic, and often undocumented. Heroin-induced leukoencephalopathy, known as "chasing the dragon" syndrome, is among the most studied. Some researchers suspect a contaminant or cutting agent in heroin, but none has been identified, and cases have occurred with contaminant-free opiates, including a woman taking triple her prescribed methadone dose and a girl intoxicated with pure morphine sulfate. Other rarely associated drugs include 2C-E ("Europa"), oxycodone, cocaine, and methadone, with unclear dose–response relationships. Chemotherapy drugs such as high-dose intravenous or intrathecal methotrexate for acute lymphoblastic leukemia can cause asymptomatic leukoencephalopathy in children and young adults, with prevalence declining over time and with dosage. 5-fluorouracil and fludarabine also induce neurotoxicity. Oral methotrexate for rheumatoid arthritis can cause leukoencephalopathy even at low doses, potentially leading to cognitive dysfunction or death.
Diagnosis
MRI advances have improved characterization of toxic leukoencephalopathy, aiding detection of injured brain tissue, though imaging severity does not always reflect clinical status. White matter may appear normal until the disease progresses further. Damage to CNS white matter, typically periventricular and other structures, is often bilateral and symmetric. Heroin-induced leukoencephalopathy frequently involves cerebellar white matter, posterior cerebral white matter, posterior limb of internal capsule, and cerebellar peduncles, with the occipital lobe most affected, though frontal, parietal, and temporal lobes may also be involved. Other toxins can extend damage to the hippocampus, dorsal medulla, and brainstem.
Treatment
No known cure or specific treatment exists for toxic leukoencephalopathy. In cases induced by medications such as methotrexate or metronidazole, the disease may gradually reduce once the medication is discontinued. Depending on the toxic source and severity of white matter damage, many patients can achieve complete clinical recovery. Coenzyme Q, vitamin C, vitamin E, and other antioxidant therapies have been suggested for heroin-induced cases but have rarely been trialed.
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