Delayed posthypoxic leukoencephalopathy

Delayed posthypoxic leukoencephalopathy (DPHL) is a demyelinating syndrome presenting as an acute neurological deterioration shortly after apparent recovery from a hypoxic-ischemic episode.

Epidemiology

Given its low frequency, there are no large numbers regarding the prevalence and incidence of delayed post-hypoxic leukoencephalopathy. Many reported cases have been secondary to carbon monoxide intoxication ¹. 

Clinical presentation

The diagnosis requires a prolonged and severe period of cerebral hypo-oxygenation, from which the patient initially recovered. After a period of relative stability that lasts typically a few weeks, there is a fairly rapid onset of neuropsychiatric deficits characterized by confusion, abnormal behavior, parkinsonism, movement disorders and cognitive deficits ^1-4.

Pathology

The exact mechanism responsible for delayed post-hypoxic leukoencephalopathy is not well understood but is believed to be related to myelin sheath damage ⁴. This accounts for white matter involvement and relative sparing of U-fibers (that have very slow myelin metabolism) ².

Radiographic features

The main imaging features of delayed post-hypoxic leukoencephalopathy reflect white matter demyelination, with MRI being the preferred modality.

CT

Early imaging features will be subtle or absent. However, CT is useful for quickly excluding other causes of delirium such as tumors or abscesses. White matter low attenuation may indicate demyelination, but is a non-specific sign ¹.

MRI

• T2/FLAIR: diffuse high signal in white matter, particularly in the centrum semiovale. Subcortical U-fibers are often spared ². 
• DWI/ADC: increased diffusion restriction, often marked ^1,4
• T1: affected white matter is typically iso- to hypointense
• T1 C+: no enhancement
• MR spectroscopy
  • ​​elevated choline and lactate peaks
  • NAA peak decreased ²

Treatment and prognosis

Supportive care is the mainstay of treatment for delayed post-hypoxic leukoencephalopathy, though it is often fatal and the evidence base is limited by the lack of cases reported.