Heroin-induced leukoencephalopathy, also known as heroin-associated spongiform leukoencephalopathy, is a toxic leukoencephalopathy caused by the inhalation of heroin fumes, which is called "chasing the dragon."

Clinical presentation

Three stages are recognised:

1. cerebellar signs and motor restlessness

2. pyramidal and pseudobulbar signs

3. spasms, hypotonic paresis, and ultimately death

Only a minority of patients progress through all three.

There may be a latent period with a subclinical evolution of white matter degeneration. Progression of the disease continues even after cessation of the toxin for up to 6 months.

Pathology

Microscopic examination of affected white matter reveals spongiform degeneration with sparing of the subcortical U-fibres ^1,4.

Radiographic features

MRI

These are similar to other toxic leukoencephalopathies with widespread symmetric white matter signal change involving both supra- and infratentorial compartments, but with a characteristic distribution ^1-4:

• posterior limb of the internal capsules with extension superiorly along the corticospinal tracts and inferiorly into pons

• cerebellar white matter and middle cerebellar peduncles (one of the causes of the so-called MCP sign)

• splenium of the corpus callosum

• midbrain white matter (e.g. medial lemniscus)

• sparing of the subcortical U-fibres and adjacent grey matter structures (e.g. dentate nuclei)

Signal characteristics of affected areas ^1,3:

• T1: hypointense

• T2/FLAIR: hyperintense

• DWI/ADC

  • elevated signal on b=1000 (T2 shine through)

  • usually facilitated (increased) ADC values

• T1 C+: no enhancement

• MRS: in the affected white matter

  • ± elevated lactate

  • ± decreased N-acetylaspartate (NAA)

Treatment and prognosis

Treatment is generally supportive.

History and etymology

The following passage is from the original description in the American Journal of Roentgenology by Ciaran F Keogh ¹:

"The term “chasing the dragon” appears to have originated in China in the 1920s and became a popular mechanism of heroin administration in the 1950s in Hong Kong because the drug was cheap but impure. A small quantity of powder is placed on aluminium foil, which is then heated underneath with a lighter or matches. The heroin liquefies into a reddish-brown glob, which moves around on the foil and emits a white vapour. The glob or “dragon” is “chased” with the lighter underneath while the vapour is sucked through a straw or pipe..."

See also

• radiological manifestations of recreational drug use