Multiple sclerosis: the plaque
- Lesion
In multiple sclerosis the immune system strips myelin from nerve fibres in the brain and cord, leaving scattered plaques over many years.
What it is
Multiple sclerosis is an autoimmune demyelinating disease of the CNS, the commonest in young adults. Plaques of myelin loss appear at different times and places, with relative sparing of axons early and axonal loss later. Most patients start with relapses and remissions; many later enter a progressive phase. Risk depends on genes (HLA-DRB1*15:01), latitude and vitamin D, and especially on prior Epstein-Barr virus infection, which is thought to be necessary though not sufficient.
Structure
- Gross: well-demarcated grey, glassy, slightly depressed plaques, often around the ventricles (Dawson fingers on MRI).
- Luxol fast blue shows sharp loss of myelin; neurofilament stains show relatively preserved axons in early plaques.
- Meningeal lymphoid follicles are found in some patients and correlate with cortical damage and severity.
Step by step
- Genetic risk and EBV infection prime autoreactive T and B cells.
- Activated lymphocytes cross the blood-brain barrier into the white matter.
- Cytokines activate macrophages and microglia that strip myelin; antibodies add damage.
- Conduction slows or blocks in demyelinated axons, causing a relapse.
- Partial remyelination and redistribution of sodium channels allow recovery.
- Over years, chronic inflammation and axonal loss cause progressive disability.
Stages of an MS plaque
| Plaque | Myelin | Cells | Axons |
|---|---|---|---|
| Active | Breaking down at the edge | Macrophages with myelin debris, perivascular lymphocytes | Mostly preserved |
| Chronic active (smouldering) | Expanding slowly at the rim | Iron-laden microglia at the edge | Progressive loss |
| Inactive | Absent | Gliosis, few oligodendrocytes | Reduced |
| Shadow | Thin new myelin | Some oligodendrocytes | Preserved |
Clinical notes
- Typical symptoms: optic neuritis, sensory disturbance, weakness, ataxia, internuclear ophthalmoplegia and bladder dysfunction.
- Disease-modifying treatments reduce relapses; MS is less frequent near the equator, including much of Colombia, than at high latitudes.
Test yourself
Think of the answer, then tap the question to see it.
Which CSF finding supports multiple sclerosis?
Oligoclonal IgG bands in CSF that are absent from serum, showing antibody production inside the CNS.
What is a shadow plaque?
A lesion edge with abnormally thin myelin from partial remyelination.
Which virus is most strongly linked to the risk of multiple sclerosis?
Epstein-Barr virus; infection appears to be necessary but not sufficient.
Elsewhere in DurgiPedia
- HLA associations with disease
- Molecular mimicry and post-infectious autoimmunity
- Immune tolerance and how autoimmunity begins
- Impulse conduction and myelin
- Glial cells: astrocytes, oligodendrocytes, microglia, Schwann cells
Connections
Microorganisms1
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Multiple Sclerosis (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.