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Demyelinating disorders of the central nervous system 

Demyelinating disorders of the central nervous system

Chapter:
Demyelinating disorders of the central nervous system
Author(s):

Siddharthan Chandran

and Alastair Compston

DOI:
10.1093/med/9780199204854.003.0241002_update_001

Update:

This chapter has been extensively rewritten (Nov 2012).

Updated on 30 May 2013. The previous version of this content can be found here.
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date: 24 April 2017

Clinicians suspect demyelination when episodes reflecting damage to white matter tracts within the central nervous system occur in young adults. The paucity of specific biological markers of discrete demyelinating syndromes places an emphasis on clinical phenotype—temporal and spatial patterns—when classifying demyelinating disorders. The diagnosis of multiple sclerosis, the most common demyelinating disorder, becomes probable when these symptoms and signs recur, involving different parts of the brain and spinal cord. Other important demyelinating diseases include post-infectious neurological disorders (acute disseminated encephalomyelitis), demyelination resulting from metabolic derangements (central pontine myelinosis), and inherited leucodystrophies that may present in children or in adults. Accepting differences in mechanism, presentation, and treatment, two observations can usefully be made when classifying demyelinating disorders. These are the presence or absence of inflammation, and the extent of focal vs. diffuse demyelination. Multiple sclerosis is prototypic for the former, whereas dysmyelinating disorders, such as leucodystrophies are representative of the latter.

Increased recognition that neurodegeneration is the dominant pathological substrate of progressive disability in multiple sclerosis highlights the mutual dependence for tissue integrity of glia and axons; and this raises the unresolved question of the relationship between focal inflammation—manifesting clinically as episodes—and neurodegeneration. The goal of future treatments, noting the emergence of more potent immunological therapies compared with current licensed disease modifying treatments and increased awareness of the neuroprotective effect of remyelination, will be to limit neurodegeneration and thus prevent disease progression.

A distinguishing feature of vertebrate development is the formation of compact glial-derived myelin ensheathing processes around axons. Myelin formation by oligodendrocytes in the central nervous system (CNS) and Schwann cells in the peripheral nervous system (PNS) has allowed the development of sophisticated and compact neural systems. Evolutionary advantage and physiological sophistication do not, however, come without their drawbacks. Several disorders, inherited and acquired, loosely grouped under the rubric of ‘demyelinating diseases’, represent conditions where, notwithstanding the intimate relationship and interdependence of glia and axons, the oligodendrocyte-myelin unit appears to be the primary and selective target involved in several important diseases of the central nervous system.

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