Heroin leukoencephalopathy is specifically seen in individuals who use heroin by inhalation, also known as “chasing the dragon.” This is different from smoking or sniffing heroin, as the heroin powder is placed on aluminum foil, then heated from underneath, and then the smoke is inhaled. The pathogenesis of the neurological damage in heroin leukoencephalopathy is unknown, as this occurs only in individuals who use heroin this way, and has not been observed in individuals who only snort or inject heroin.
Clinically, the presentation of leukoencephalopathy occurs in 3 stages: initially, pseudobulbar speech, cerebellar signs and motor restless are typically observed. After 2-4 weeks, some patients will progress to a second stage that typically has rapid increase of cerebellar symptoms and additional features, such as pyramidal signs, hyperreflexia, spastic hemiplegia or quadriplegia, tremor, myoclonus, athetosis and chorea. After a few more weeks, a subset of those patients (approximately 25%) will progress to the final terminal stage, with the following: stretching spasms, hypotonic/areflexic paresis, akinetic mutism, central pyrexia followed by subsequent death.
On Brain MRI there is diffuse, symmetrical white matter hyperintensity in the supratentorial and infratentorial compartments on T2, and FLAIR sequences in the cerebellum, posterior cerebrum and posterior limbs of the internal capsule are seen as well, extending inferiorly into the pontine corticospinal tracts and superiorly into the perirolandic subcortical white matter. On Diffusion weighted imaging (DWI), an increased signal in the periventricular white matter may be present with corresponding low signal on apparent diffusion coefficient (ADC) maps. Subcortical U-fibers are usually spared, as well as the adjacent grey matter structures and the frontal lobes.
References:
1. Hagel J, Andrews G, Vertinsky T, et al. “Chasing the dragon”-imaging of heroin inhalation leukoencephalopathy. Can Assoc Radiol J. 2005;56(4):199–203.
2. https://radiopaedia.org/articles/chasing-the-dragon-sign-toxic-leukoencephalopathy