Multiple Sclerosis

Slide 1 · Multiple Sclerosis

Immune-mediated CNS demyelination

Pathogenesis · morphology · clinical correlations

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain the immune mechanisms and genetic–environmental predisposition of MS.

Recognize macroscopic, microscopic and spatial patterns of demyelinating plaques.

Relate lesion location and disease course to clinical findings and investigations.

Distinguish MS from selected other demyelinating syndromes.

Slide 3 · Multiple sclerosis: Defining pathology

Acquired immune-mediated demyelination primarily within the CNS.

Patchy lesions often affect widely separated white matter sites.

Secondary axonal injury and gray matter pathology contribute to long-term disability.

Slide 4 · Demyelination is not failed myelin synthesis

Demyelination: Destruction of previously formed myelin.

Axons are relatively preserved early, but can become damaged with time.

Inherited leukodystrophies involve abnormal myelin synthesis or turnover.

Slide 5 · Myelin loss disrupts axonal signaling

Preserved conduction insulation

Continuous myelin segments support efficient impulse propagation.

Inflammatory demyelination

Loss of insulation causes impaired signal transmission; Axons initially persist.

Schematic — segment count and lesion size are illustrative, not quantitative.

Slide 6 · Why the symptoms can initially improve

Early neurologic deficits arise partly from impaired conduction in demyelinated tracts.

Inflammation may decline following an attack, permitting partial functional recovery.

Remyelination is limited; Cumulative axonal damage restricts later recovery.

Slide 7 · Dissemination in time and space

Time

Distinct episodes of neurologic dysfunction

Clinical remissions may be incomplete

New manifestations can emerge later

Space

Separate CNS lesions at different locations

Different tracts explain different deficits

A single symptom does not define the full lesion burden

Slide 8 · Multifocal anatomy explains variable findings

Variable CNS sites

Different clinical deficits

Conceptual map — not an MRI, anatomical section, or lesion prevalence map.

Slide 9 · MS has a characteristic epidemiologic pattern

Textbook estimate: Approximately 1 per 1,000 persons in much of the United States and Europe.

Clinical onset can occur at many ages; Childhood and onset after age 50 are uncommon.

Females are affected more than twice as often as males.

Slide 10 · Most patients initially have a relapsing course

Neurologic attacks and remissions are separated by variable intervals.

Deficits may last weeks to months; Intervals between attacks may be long.

Recovery after attacks is often gradual and incomplete.

Slide 11 · Secondary progressive MS

A proportion of relapsing–remitting patients later accumulate disability steadily.

Relapses may become less prominent while progression continues.

Progressive decline can occur despite suppression of acute relapses.

Slide 12 · Primary progressive MS

Disability progresses from clinical onset.

Sustained neurologic deterioration occurs without a preceding relapsing–remitting phase.

Intermittent improvement, if present, is limited.

Slide 13 · Three clinical trajectories are not equivalent

The distinction concerns the temporal pattern of neurologic disability.

Relapsing–remitting

Secondary progressive

Primary progressive

Horizontal axis: Time · Vertical axis: Neurologic disability (qualitative)

Illustrative clinical trajectories — qualitative axes, not patient data or estimated probabilities.

Slide 14 · Relapses and progression are distinct dimensions

Acute inflammatory activity contributes to clinical attacks.

Steady disability accumulation reflects additional neurodegenerative pathology.

Effective relapse prevention does not completely prevent late deterioration.

Slide 15 · MS has both genetic and environmental components

No single causative variant explains the disease.

Familial aggregation supports inherited susceptibility.

Environmental exposure is important and interacts with susceptibility.

Slide 16 · Family and twin studies indicate susceptibility

~15-fold greater incidence with an affected first-degree relative.

The reported increase is ~150-fold with an affected monozygotic twin.

These comparisons indicate strong susceptibility, not deterministic inheritance.

Relative incidence reported by Robbins

First-degree relative

~15-fold

Monozygotic co-twin

~150-fold

Associations, not individual probabilities

Conceptual schematic — not a specimen or patient image.

Slide 17 · MHC region is a major genetic association

A strong relationship exists with a major histocompatibility complex DR haplotype.

Antigen presentation biology fits the proposed autoimmune mechanism.

MHC association alone cannot account for the variability of clinical course.

Slide 18 · Immune regulatory genes contribute

Genome-wide associations include genes for IL-2 and IL-7 receptors.

Additional associations involve B-cell functions and cytokine signaling.

Other associated loci regulate costimulation and intracellular immune signaling.

Slide 19 · Genetics does not explain clinical variability

Only part of the inherited predisposition is currently accounted for.

Many associated immune loci are shared with other autoimmune disorders.

Genetic studies have not explained why outcomes differ substantially between patients.

Slide 20 · Geographic variation implicates environment

MS is diagnosed more frequently in populations farther from the equator.

The mechanism of this geographic association remains uncertain.

Association should not be interpreted as proof of a single environmental cause.

Slide 21 · EBV exposure is closely associated with MS

Large epidemiologic studies strongly link prior Epstein–Barr virus infection to MS.

EBV infection as likely necessary, but insufficient alone.

Most EBV-exposed people do not develop MS.

Prior EBV infection

Important susceptibility context

Necessary model; Not sufficient by itself

Conceptual schematic — not a specimen or patient image.

Slide 22 · Timing of EBV infection appears important

A pronounced increase in risk with later EBV infection.

The reported ~40-fold association pertains to infection during adolescence rather than early childhood.

An epidemiologic association does not itself establish a complete causal mechanism.

Slide 23 · Molecular mimicry offers a mechanistic link

EBV nuclear antigen 1 (EBNA1) can show immunologic cross-reactivity with glial proteins.

Cross-reactive antibodies and T cells are both plausible participants.

Mimicry is a proposed contributing mechanism—not a defined universal autoantigen.

EBNA1 epitope

Cross-reactive immune response

Glial protein recognition

Conceptual schematic — not a specimen or patient image.

Slide 24 · Autoimmune pathways converge on myelin injury

Multiple immune processes act together; The relevant antigenic targets remain incompletely defined.

Susceptibility + environment

T- and B-cell responses

Macrophage / microglial activation

Myelin injury

Biologic sequence is a teaching abstraction: Exact autoantigen and causal weighting remain uncertain.

Schematic: Cellular interactions are bidirectional in vivo.

Slide 25 · The classic T-cell model is incomplete

Experimental autoimmune encephalomyelitis historically emphasized myelin-reactive CD4 and CD8 T cells.

Th1/Th17 responses and activated macrophages can participate in myelin destruction.

Human MS is not fully explained by these animal models.

Slide 26 · Animal models have limitations

Immunization with myelin proteins and strong adjuvants induces inflammatory demyelination experimentally.

Such models may exaggerate the role of T cells relative to human disease.

Mechanistic extrapolation should not be confused with direct evidence in patients.

Slide 27 · B cells are central to contemporary models

Benefit from B-cell depletion supports an important pathogenic role.

Clonally expanded B cells occur in CSF.

B-cell function is more complex than simply producing antibody.

Slide 28 · Three potential pathogenic roles of B cells

Production of antibodies reactive with glial proteins, including GlialCAM.

Presentation of self antigens that may activate T cells.

Secretion of inflammatory cytokines that amplify immune injury.

Autoreactive B cell

Antibodies

Present to

T cells

Cytokines

Conceptual schematic — not a specimen or patient image.

Slide 29 · Intrathecal B-cell responses are expanded

Somatically mutated, clonally expanded B cells have been detected in CSF.

Increased CSF IgG and oligoclonal bands reflect compartmentalized antibody production.

These findings support an intrathecal humoral immune response.

Slide 30 · Meningeal lymphoid structures link immunity to severity

B-cell-rich inflammatory foci may organize into lymphoid follicles in the meninges.

An association between follicle burden and disease severity.

Meningeal immune activity is associated with cortical pathology.

Leptomeningeal compartment

Subpial cortex

B-cell-rich inflammatory focus

Conceptual schematic — not a specimen or patient image.

Slide 31 · EBV biology may intersect with B-cell disease

EBV activates B cells, potentially increasing autoreactive antibody production.

Immune cross-reactivity may connect viral epitopes and glial targets.

Neither hypothesis establishes EBV as the sole explanation for MS.

Slide 32 · Inflammation and degeneration coexist

Active attacks are linked to immune-mediated myelin injury.

Progression includes slowly enlarging plaques and diffuse low-grade inflammation.

Cortical damage and secondary axonal loss contribute to persistent deficits.

Slide 33 · Progressive pathology extends beyond acute plaques

Slowly enlarging white matter lesions may persist in progressive disease.

Diffuse white matter inflammation continues at low grade.

Subpial cortical injury is important to neurodegenerative progression.

Slide 34 · Gross plaques are demarcated and firm

On fresh sections, plaques are firmer than adjacent white matter.

Lesions appear glassy, gray-tan, somewhat depressed and irregular.

Their firmness is the basis of the term “sclerosis.”

Slide 35 · Lesions vary in size and may coalesce

Small microscopic foci can be found alongside large confluent plaques.

Myelin stains reveal sharper borders than some routine preparations.

Lesion size alone does not define clinical severity.

Slide 36 · Characteristic anatomic distribution

Common sites include periventricular white matter and corpus callosum.

Optic nerves and chiasm, brainstem and cerebellum are also affected.

Spinal cord and long ascending or descending tracts may contain plaques.

Slide 37 · Periventricular lesions are a classic site

Plaques frequently occur adjacent to lateral ventricles.

Corpus callosum involvement illustrates the white matter predilection.

Distribution provides an anatomic framework for MRI interpretation.

Slide 38 · Cortical demyelination is also important

Extensive subpial demyelination can affect thin myelinated cortical fibers.

Subpial lesions as a hallmark of MS pathology.

These lesions are often associated with B-cell-rich leptomeningeal foci.

Slide 39 · Active plaques show ongoing myelin destruction

Abundant lipid-laden or foamy macrophages contain ingested myelin debris.

Lymphocytes cluster around vessels, particularly near the lesion edge.

Small-vein-centered inflammation is characteristic of active lesions.

Slide 40 · Perivascular cuffs identify local inflammation

Lymphocytes may form concentric cuffs around small vessels.

Inflammatory infiltrates are typically prominent around the active border.

This must be interpreted with demyelination and other morphological features.

Small vessel

Perivascular lymphocytes

Conceptual schematic — not a specimen or patient image.

Slide 41 · Macrophages are a direct clue to active breakdown

Foamy macrophages indicate phagocytosis of myelin lipids.

Active plaques are more cellular than inactive gliotic plaques.

Macrophage abundance reflects activity, not specific proof of the initiating autoantigen.

Slide 42 · Myelin loss exceeds early axonal loss

Stains for myelin often show extensive or complete local loss.

Axonal markers can show relative preservation in the same active lesion.

With progression and chronicity, axon numbers can markedly decline.

Same lesion: Different tissue compartments

Myelin: Markedly depleted

Axons: Relatively retained

Relative preservation is not permanent

Conceptual schematic — not a specimen or patient image.

Slide 43 · Astrocytic gliosis evolves as plaques age

Reactive astrocytes become conspicuous during the tissue response.

Inflammatory cells wane as active lesions become quiescent.

Sustained gliosis is a defining feature of old sclerotic plaques.

Slide 44 · Inactive plaques lack macrophage-rich infiltrates

Inflammatory infiltrates are sparse or absent.

Myelin remains severely depleted, and oligodendrocyte nuclei are reduced.

Reactive gliosis and chronic axonal loss are prominent.

Slide 45 · Smoldering plaques have an active border

Progressive MS can contain lesions with a hypocellular inactive-like center.

Activated microglia or macrophages occupy a rim at the lesion periphery.

This pattern differs from a uniformly active acute plaque.

Slide 46 · Shadow plaques represent limited remyelination

The affected white matter is less pale than a fully demyelinated plaque.

Thinner-than-normal myelin sheaths can be demonstrated.

Remyelination is partial and often most apparent toward the plaque edge.

Slide 47 · Remyelination does not fully restore structure

Surviving oligodendrocytes may remyelinate some axons.

Many remaining axons within established lesions stay unmyelinated.

Secondary axonal depletion limits the opportunity for later functional recovery.

Slide 48 · Plaque histology changes with activity

Active plaque

Macrophages + inflammation

Inactive plaque

Hypocellular + gliosis

Smoldering plaque

Quiet center; Active rim

Shadow plaque

Thin residual myelin

Slide 49 · Compare major plaque morphologies

Plaque pattern

Predominant finding

Structural implication

Active

Foamy macrophages; Perivascular lymphocytes

Ongoing demyelination

Inactive

Gliosis; Sparse inflammation

Chronic demyelinated scar

Smoldering

Quiet center; Activated rim

Persistent edge activity

Shadow

Thin myelin sheaths

Partial remyelination

Slide 50 · Histologic methods answer different questions

Myelin stains delineate the extent of demyelination.

Neurofilament immunostaining assesses residual axons.

Macrophage markers emphasize phagocytic inflammatory burden.

Myelin stain

Demyelinated area

Neurofilament

Residual axons

Macrophage marker

Inflammatory activity

Conceptual schematic — not a specimen or patient image.

Slide 51 · Optic neuritis may be the first presentation

Inflammation of the optic nerve can cause unilateral visual impairment.

It is a frequent presenting event but is not specific to MS.

Population-dependent subsequent MS occurrence after optic neuritis.

Slide 52 · Optic neuritis is not equivalent to MS

An approximate 10–50% subsequent MS range after isolated optic neuritis.

Population selection strongly affects that estimate.

An isolated event does not establish the historical relapsing–disseminated phenotype.

Slide 53 · Brainstem plaques affect cranial pathways

Brainstem involvement may cause nystagmus and cranial nerve deficits.

Ataxia can reflect interruption of brainstem and connected cerebellar pathways.

Distinct localizations explain the broad variety of clinical syndromes.

Slide 54 · Internuclear ophthalmoplegia localizes to the MLF

The medial longitudinal fasciculus links pathways coordinating horizontal eye movement.

An MS plaque can interrupt this connection and cause internuclear ophthalmoplegia.

Recognizing the tract explains the ocular motor findings.

Eye movement center

Ocular motor nuclei

MLF lesion interrupts coordination

Conceptual schematic — not a specimen or patient image.

Slide 55 · Spinal cord plaques impair long-tract function

Motor and sensory deficits may involve limbs and trunk.

Descending pathway disruption may produce spasticity.

Autonomic pathway dysfunction can impair bladder and bowel control.

Spinal cord

Long-tract dysfunction

Conceptual schematic — not a specimen or patient image.

Slide 56 · Localize symptoms to the affected system

Predominant symptom

Likely affected region

Clinicopathologic principle

Unilateral visual impairment

Optic nerve

Optic neuritis

Internuclear ophthalmoplegia

Medial longitudinal fasciculus

Brainstem tract interruption

Ataxia or nystagmus

Brainstem / cerebellar pathways

Coordination and eye-movement networks

Spasticity, sensory changes

Spinal cord tracts

Long-tract dysfunction

Slide 57 · CSF provides evidence of intrathecal immunity

Total CSF protein is usually normal or only mildly elevated.

Moderate pleocytosis occurs in a subset of patients.

CSF IgG may be increased, with oligoclonal IgG bands usually detectable.

Slide 58 · Oligoclonal IgG bands have a mechanistic meaning

Bands suggest expanded antibody-producing B-cell clones within the CNS compartment.

They support intrathecal immune activity but do not uniquely identify MS.

Interpret laboratory findings with compatible clinical and anatomic evidence.

Slide 59 · MRI is central to assessment

Magnetic resonance imaging is prominent in monitoring MS lesions and progression.

Anatomic distribution can be related to neurologic symptoms.

Morphologic and temporal assessment complement the clinical examination.

Slide 60 · Clinical, CSF and imaging findings are complementary

CSF

Increased intrathecal IgG

Oligoclonal IgG bands

Normal or mildly elevated total protein

Moderate pleocytosis in some cases

MRI

Prominent tool for assessing disease

Visualizes distribution of CNS lesions

Important for monitoring course

Interpret alongside clinical findings

Slide 61 · Neuromyelitis optica differs from MS

Multiple sclerosis

Multifocal CNS plaque distribution

Prominent immune-mediated myelin destruction

Often relapsing–remitting onset

AQP4-associated NMO

Often severe optic and spinal attacks

Aquaporin-4 autoantibody-associated astrocyte injury

Necrosis and complement-associated pathology may occur

Slide 62 · ADEM and MOG-associated disease are distinct

Multiple sclerosis

Often recurrent attacks or progression

Plaques of differing ages and activity

Meningeal B-cell and cortical pathology

ADEM / MOGAD

ADEM often acute and monophasic

Commonly follows antecedent infection

Encephalopathy may dominate clinical presentation

Slide 63 · Other demyelinating processes require separation

Progressive multifocal leukoencephalopathy causes infectious myelin destruction.

Leukodystrophies affect myelin synthesis or turnover by inherited mechanisms.

Osmotic demyelination follows major osmotic disturbance; It is not typical MS.

Slide 64 · Immunomodulatory therapy primarily targets inflammation

Broad use of immunomodulatory and immunosuppressive treatments.

These treatments substantially suppress acute relapses.

The later neurodegenerative stage is only partially controlled by immune treatment.

Slide 65 · Anti-CD20 therapy supports B-cell importance

B-cell-depleting anti-CD20 therapies are emphasized treatment discussion.

Their clinical efficacy reinforces an important causal role for B cells.

Treatment response does not specify which B-cell function is dominant in every patient.

Slide 66 · Early effective treatment may reduce later disability

Accumulating evidence supporting prompt effective immunomodulation.

Suppression of inflammatory activity is an important preventive opportunity.

Residual progression highlights a continuing need to address neurodegeneration.

Slide 67 · Case 1: An optic pathway presentation

A young adult develops a unilateral episode of visual impairment.

A subsequent neurologic episode affects a different CNS pathway.

Question: Which pathologic feature unifies spatially distinct events?

Slide 68 · Case 1: Clinicopathologic reasoning

The recurrent, multifocal pattern is compatible with a CNS demyelinating process.

Inflammatory plaques at different sites account for different deficits.

Confirmation requires appropriate clinical evaluation and exclusion of mimics.

Slide 69 · Case 2: Progression despite fewer relapses

A patient initially has attacks with partial recovery.

Later, disability slowly accumulates while overt attacks become infrequent.

Question: What pathological processes can sustain the decline?

Slide 70 · Case 2: Explain disability accumulation

Secondary progressive disease is suggested by steady deterioration after a relapsing phase.

Chronic active plaques, cortical injury and axonal loss contribute to decline.

Anti-inflammatory control of relapses does not fully block neurodegeneration.

Slide 71 · Integrated pathology of multiple sclerosis

Immune dysregulation causes multifocal destruction of previously normal CNS myelin.

Active plaques contain inflammatory cells; inactive lesions show gliosis; chronic lesions lose axons.

Anatomic distribution determines deficits, while tissue injury and repair failure shape progression.