Lesional demyelinations of the central nervous system

Multiple sclerosis and other demyelinating diseases of the central nervous system (CNS) produce lesions (demyelinated areas in the CNS) and glial scars or scleroses. They present different shapes and histological findings according to the underlying condition that produces them.

Demyelinating diseases are traditionally classified in two kinds: demyelinating myelinoclastic diseases and demyelinating leukodystrophic diseases. In the first group a normal and healthy myelin is destroyed by a toxic, chemical or autoimmune substance. In the second group, myelin is abnormal and degenerates. The second group was denominated dysmyelinating diseases by Poser Therefore, since Poser demyelinating diseases normally refers to the myelinoclastic part.

Demyelinating diseases of the CNS can be classified according to their pathogenesis into five non-exclusing categories: demyelination due to inflammatory processes, viral demyelination, demyelination caused by acquired metabolic derangements, hypoxic–ischaemic forms of demyelination and demyelination caused by focal compression.

The four non-inflammatory possibilities are:

All these four types of demyelination are non-inflammatory and different to MS even if some leukoencephalopathies can produce similar lesions

Typical lesions are similar to those of MS, but there are four kinds of atypical inflammatory demyelinating lesions: Ring-like (antibody-mediated), megacystic (tumefactive), Balo-like, and diffusely-infiltrating lesions.

The list of the diseases that produce CNS demyelinating lesions is not complete, but it includes:

A special characteristic that makes a difference between MS and the several kinds of ADEM is the structure of the lesions, being strictly perivenous in ADEM and showing a confluence around veins in MS. Given that ADEM can be multiphase sometimes and MS can appear in children, this characteristic is often considered as the line that separates both conditions.

The most typical of perivenous demyelination is ADEM

ADEM can present plaque-like lesions which are indistinguishable from MS Nevertheless, ADEM White Matter appears intact under Magnetization Transfer MRI, while MS shows problems (See NAWM). Besides ADEM does not present "black holes" under MRI (zones with axonal damage) and lesions develop strictly around veins instead of the more relaxed rule for MS

As with MS, several patterns have been described inside NMO, but they are heterogeneus inside the same individual, reflecting stages in the lesion evolution:

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