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Demyelinating diseases are traditionally classified into two types: demyelinating myelinoclastic diseases and demyelinating leukodystrophic diseases. In the first group, a healthy and normal myelin is destroyed by toxic substances, chemicals, or autoimmune reactions.
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. [3]
Demyelination is the loss of the myelin sheath insulating the nerves, and is the hallmark of some neurodegenerative autoimmune diseases, including multiple sclerosis, acute disseminated encephalomyelitis, neuromyelitis optica, transverse myelitis, chronic inflammatory demyelinating polyneuropathy, Guillain–Barré syndrome, central pontine ...
Some clusters of activated microglia, axonal transection and myelin degeneration are present. [7] [8] [9] Leaks in the blood–brain barrier appear and immune cells infiltrate, causing demyelination. [10] and axon destruction. [11] Multiple sclerosis differs from other idiopathic inflammatory demyelinating diseases in its confluent subpial ...
Even within a fascicle, demyelination does not affect nerves uniformly. For example, in the early stages, demyelination can be seen at the edge of fascicles near the periphery of the nerve, and in later stages the demyelination is diffusely seen within the entirety of a fasicle. [5] [16] Damage to the myelin sheath of nerves is a nerve injury.
Inflammatory demyelinating diseases (IDDs), sometimes called Idiopathic (IIDDs) due to the unknown etiology of some of them, are a heterogenous group of demyelinating diseases - conditions that cause damage to myelin, the protective sheath of nerve fibers - that occur against the background of an acute or chronic inflammatory process.
Two different mechanisms of axon destruction are acting in MS. First of all, there is a diffuse axon degeneration, probably related to the NAWM appearance. Later, there is a second axonal damage mechanism localized in old demyelinating lesions, probably produced by B-Cells.
Studies suggest that the degeneration happens as a result of the axonal protein NMNAT2, being prevented from reaching all of the axon. [56] Demyelination of axons causes the multitude of neurological symptoms found in the disease multiple sclerosis. Dysmyelination is the abnormal formation of the myelin sheath.