Toxic encephalopathy

Drugs and medications

Toxic exposure to illicit substances is often accompanied by severe vascular catastrophes and demyelination.

• Cocaine: Promotes ischemic and hemorrhagic strokes. Hemorrhages occur twice as often and are usually localized in the subarachnoid space or intracerebral structures (basal ganglia, thalamus). The mechanism is associated with a sympathomimetic spike in blood pressure, which can lead to the rupture of aneurysms or arteriovenous malformations. Adulterants play an important role: the anthelmintic drug levamisole causes multifocal inflammatory leukoencephalopathy (lesions are hyperintense on T2-FLAIR with a rim of restricted diffusion).
• Opioids (heroin): Ischemic strokes are the most frequent complication. The globus pallidus is often the target. A specific variant is the "chasing the dragon" syndrome from inhaling heroin vapors. MRI shows extensive symmetrical hyperintensity of the white matter: the posterior limb of the internal capsule (crus posterius capsulae internae), medial lemniscus (lemniscus medialis), and pyramidal tracts. The cortex and cerebellar dentate nuclei (nucleus dentatus) remain intact.
• Ecstasy (MDMA): Causes a massive release of serotonin, leading to severe vasoconstriction and necrosis of the most vulnerable zones—the occipital cortex and globus pallidus.

Alcohol and surrogates

Chronic alcohol abuse leads to diffuse and focal lesions.

1. Brain atrophy: Begins with infratentorial structures (atrophy of the cerebellar vermis — vermis), then extends to the frontal and temporal lobes. If alcohol affects the fetus, it inhibits the maturation of Bergmann glial fibers, causing marked cerebellar atrophy.
2. Marchiafava-Bignami disease: A rare complication associated with the consumption of low-quality red wine and B-vitamin deficiency. Demyelination and necrosis of the corpus callosum (corpus callosum) occur. In the acute phase, MRI shows hyperintensity on T2 and restricted diffusion; in the chronic phase, necrosis of the splenium and genu.
3. Methanol poisoning: Toxicity is mediated by formic acid. The primary target is the putamen (putamen). Scans show zones of necrosis (hyperintense on T2), sometimes with hemorrhages.
4. Ethylene glycol and diethylene glycol: Cause cerebral edema and white matter involvement (predominantly in the temporo-parieto-occipital region).

Carbon monoxide, metals, and solvents

Specific toxins have preferential locations in the central nervous system.

• Carbon monoxide (CO): Has a very high affinity for hemoglobin, causing severe hypoxia. A characteristic sign is bilateral necrosis of the globus pallidus (globus pallidus). In severe cases, the white matter is affected.
• Heavy metals:
• Manganese: Accumulates in the basal ganglia (appears bright on T1 without contrast). Often found in alcoholic liver cirrhosis.
• Mercury: Selectively affects the cerebellar vermis and visual cortex.
• Organic solvents (toluene): Cross the blood-brain barrier upon inhalation. Cause diffuse demyelination and axonal loss (diffuse T2 signal hyperintensity).

Iatrogenic and metabolic encephalopathies

A rare complication is gadolinium-induced toxic encephalopathy. It occurs in patients with acute renal failure after intravenous contrast administration. Gadolinium crosses the blood-CSF barrier—a bright signal from the CSF is visible on T2-FLAIR. The prognosis is favorable.

Inherited metabolic disorders may debut in adults. For example, X-linked adrenoleukodystrophy (affecting the corticospinal tracts with restricted diffusion and contrast enhancement) or Krabbe disease (also affecting the corticospinal tract, but without involvement of the lower brainstem and without contrast enhancement).

Class and exam questions

What else to study on this topic

• Pathogenesis of demyelination in Marchiafava-Bignami disease
• Specifics of blood-CSF barrier impairment following gadolinium administration
• Cannabis-induced strokes: the role of vasculopathy
• Differential diagnosis of globus pallidus necrosis on MRI
• Neurotoxicity of levamisole as a contaminant in illicit drugs

Other topics in the Neuroimaging section

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