Multiple Sclerosis

Multiple sclerosis is a chronic immune-mediated disease of the central nervous system characterised by inflammatory demyelination, axonal injury, and gliosis. Its hallmark lesions are demyelinating plaques disseminated in space and time throughout the brain and spinal cord white and grey matter.

Definition

Multiple sclerosis is a chronic inflammatory, immune-mediated disorder of the central nervous system in which focal demyelinating plaques - with loss of myelin, relative early preservation and later loss of axons, and reactive gliosis - are disseminated in space and time through the brain and spinal cord.

Scope

The entry covers the neuropathology of multiple sclerosis - the demyelinating plaque, inflammatory destruction of myelin, axonal and neuronal injury, and the principle of dissemination in space and time. It is a reference and educational overview and does not provide diagnostic or treatment instructions.

Core questions

• What defines the multiple sclerosis plaque, and how does it differ between active and chronic lesions?
• What is meant by dissemination in space and time?
• How do demyelination and axonal injury together account for the relapsing and progressive features of the disease?

Key concepts

• Demyelinating plaque
• Inflammatory demyelination
• Dissemination in space and time
• Axonal injury and transection
• Reactive gliosis (glial scar)
• Active versus chronic lesions
• Grey-matter and cortical involvement

Mechanisms

The defining lesion of multiple sclerosis is the demyelinating plaque, a circumscribed area in which the immune system attacks and strips myelin from central nervous system axons. Active lesions show inflammatory infiltrates and ongoing myelin breakdown with lipid-laden macrophages, whereas chronic lesions become demyelinated, gliotic scars. Although myelin is the principal target, axons are also injured and transected, and this axonal and neuronal loss is an important substrate of accumulating, irreversible disability. Lesions characteristically arise at multiple sites and at different times, giving rise to the clinical and radiological principle of dissemination in space and time that underlies how the disease is recognised. Grey-matter and cortical demyelination is increasingly recognised alongside the classic white-matter plaques.

Clinical relevance

The dissemination of demyelinating lesions in space and time produces the relapsing and progressive neurological deficits that characterise multiple sclerosis, and this pathology underlies the diagnostic criteria used to identify the disease. This entry is for reference and education; it describes disease mechanisms and is not a source of diagnostic or treatment advice.

Epidemiology

Multiple sclerosis is a leading cause of non-traumatic neurological disability in young and middle-aged adults. It typically presents in early adulthood, affects women more often than men, and shows a latitude gradient in prevalence that has informed hypotheses about environmental contributions.

Evidence & guidelines

The diagnosis of multiple sclerosis rests on consensus criteria - the McDonald criteria and their revisions - that operationalise dissemination in space and time using clinical and imaging evidence. Authoritative reviews synthesise the pathology and biology of the disease.

History

Multiple sclerosis was characterised clinically and pathologically in the nineteenth century through correlation of disseminated sclerotic plaques with progressive neurological deficits. The recognition that lesions are disseminated in space and time became the organising principle for diagnosis, later refined by imaging-based McDonald criteria, while studies of axonal injury reshaped understanding of how disability accumulates.

Debates

Are multiple sclerosis lesions pathologically homogeneous?

Studies of active demyelinating lesions have described differing patterns of myelin loss and immune involvement, raising the question of whether multiple sclerosis is pathologically uniform or comprises distinct mechanisms; the extent and stability of such heterogeneity remain debated.

Key figures

• Claudia Lucchinetti
• Daniel Reich

Seminal works

• reich-2018
• noseworthy-2000

Frequently asked questions

What is a multiple sclerosis plaque?

A plaque is a focal demyelinating lesion of the central nervous system in which myelin has been stripped from axons by an immune-mediated process, with inflammation in active lesions and gliotic scarring in chronic ones. Plaques are the hallmark pathology of the disease.

What does 'dissemination in space and time' mean?

It refers to the appearance of demyelinating lesions at multiple sites in the central nervous system (space) and at different points over the disease course (time); this pattern is central to how multiple sclerosis is defined and diagnosed. It is a descriptive principle, not treatment advice.