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PH-NE14

Other demyelinating diseases

How antibodies to astrocyte water channels (NMOSD) or to myelin (MOGAD, ADEM), a virus that kills oligodendrocytes (PML), an osmotic shock and inherited enzyme defects strip central myelin, and how each is told apart from MS.

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  • 6 steps · 10 questions
  • 3D normal anatomy

By the end, you can

  • Explain how central myelin depends on oligodendrocytes and astrocytes, and which cell or process each demyelinating disease targets.
  • Explain how aquaporin-4 antibodies injure astrocytes first, and relate the aquaporin-rich sites to severe optic neuritis, long spinal cord lesions and the area postrema syndrome.
  • Compare MOG antibody disease and acute disseminated encephalomyelitis with NMOSD and multiple sclerosis in cause, course and lesion pattern.
  • Explain how JC virus reactivation and too-rapid correction of chronic hyponatraemia destroy oligodendrocytes, and outline how leukodystrophies arise.
  • Recognise the classic appearances, criteria and tests that tell these diseases apart from MS, and explain how immunotherapies, immune recovery and stem cell transplantation act on the mechanism.

What it is

Demyelinating diseases destroy myelin, or the cells that make and support it, while the axons are at first relatively spared. Besides multiple sclerosis, central myelin is lost through an antibody attack (neuromyelitis optica spectrum disorder, NMOSD, and MOG antibody-associated disease, MOGAD), a single post-infectious attack (acute disseminated encephalomyelitis, ADEM), viral infection of oligodendrocytes (progressive multifocal leukoencephalopathy, PML), osmotic injury (osmotic demyelination syndrome) and inherited defects of myelin metabolism (leukodystrophies).

6 types to tell apart
NMOSD (aquaporin-4 antibody)
Antibodies against the astrocyte water channel aquaporin-4 kill astrocytes, and myelin is lost secondarily; relapsing, with severe optic neuritis and long spinal cord lesions.
MOG antibody-associated disease (MOGAD)
Antibodies against myelin oligodendrocyte glycoprotein on the outer surface of myelin; optic neuritis, myelitis or ADEM, often with good recovery.
Acute disseminated encephalomyelitis (ADEM)
A single, widespread attack of inflammation round small veins after an infection, mostly in children, with drowsiness or confusion.
Progressive multifocal leukoencephalopathy (PML)
JC virus reactivates when T-cell immunity fails and destroys oligodendrocytes; relentlessly progressive unless immunity recovers.
Osmotic demyelination syndrome
Oligodendrocytes, classically in the centre of the pons, die when a chronically low sodium is raised too quickly; there is no inflammation.
Leukodystrophies
Inherited defects in building or breaking down myelin lipids, such as X-linked adrenoleukodystrophy, metachromatic leukodystrophy and Krabbe disease: symmetric, steadily progressive loss of white matter.

US spelling: centre → center.

Normal function

The cells that make and guard central myelin

Central myelin is made by , each wrapping segments of several axons; how myelin speeds conduction, and how conduction fails without it, is taught in the multiple sclerosis lesson. Oligodendrocytes also support the axons they wrap metabolically, so an axon that stays bare for long can degenerate. The outermost layer of the carries myelin oligodendrocyte glycoprotein (MOG), a minor protein but the one most exposed to antibodies.

cover the with their end-feet, part of the blood–brain barrier. The end-feet are packed with the water channel aquaporin-4, which is especially abundant in the optic nerves, the spinal cord and the tissue round the ventricles. One such site is the area postrema, a vomiting centre in the floor of the fourth ventricle whose capillaries are naturally leaky. Astrocytes also clear potassium and glutamate and support oligodendrocytes: when astrocytes die, the myelin nearby is lost too.

Myelin is mostly lipid, and its lipids are constantly renewed: lysosomal enzymes break down sulfatides and galactocerebroside, and peroxisomes shorten very-long-chain fatty acids. Oligodendrocytes, like other brain cells, also keep their volume steady when plasma sodium changes, by gaining or shedding small solutes. Each of these supports is the weak point of one disease in this lesson.

Point to it on the model