Leukoencephalopathy is shorthand for a disease that preferentially manifests as damage to the white matter of the brain. While often referred to as “demyelinating diseases”, axonal damage is present in all of these disorders (in contrast to nearly pure myelin loss which can be seen cases of acute inflammatory demyelinating polyneuropathy/ Guillain-Barre syndrome). However, partial preservation of axons and minimal detectable loss of neuronal cell bodies separate leukoencephalopathies from other major classes of CNS diseases (ischemic, degenerative, etc.). While leukoencephalopathies have varying presentations and pathologies, neuroimaging characteristically demonstrates that most of the action is in the white matter.  

The traditional primary physiologic function of myelin is to enhance axonal action potential conduction. Loss of myelin can result in either decreased conduction velocity or overt conduction block depending on the extent and location of the demyelination and the subsequent alteration in axonal ion channel distribution and kinetics. Myelin sheath may also have a protective function in shielding axons from potentially toxic local factors such as edema, ionic disturbances, and pathogenic cytokines.

Broadly speaking leukoencephalopathies can be divided into those that are inborn/genetic and those that are acquired. Genetic disorders may be subdivided into those that affect myelin development (called leukodystrophies) and those that affect white matter through other means (e.g. inherited arteriopathy). Acquired disorders of white matter can be divided into toxic/metabolic, infectious, or immune-mediated.

These disorders are discussed in this section.  To start off, we recommend the video presentation by gliageek, "Demyelinating Diseases," which you can access by clicking the first "video link" below.

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