Progressive Multifocal Leukoencephalopathy

Slide 1 · Progressive Multifocal

Leukoencephalopathy

JC polyomavirus • CNS demyelination • Neuropathologic diagnosis

Clinical–pathologic teaching lecture

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain how JC polyomavirus produces a demyelinating CNS infection.

Recognize lesion architecture and diagnostic cytopathology.

Integrate the clinical course, imaging, virology, and biopsy findings.

Distinguish PML progression from selected mimics and immune reconstitution.

Slide 3 · Clinical entry point: Progressive focal deficits

Hypothetical teaching scenario, not a reported patient.

An immunosuppressed patient develops steadily worsening focal neurologic deficits.

Brain MRI reveals multifocal abnormalities predominantly involving white matter.

The conjunction of immune risk, tempo, and lesion distribution raises PML.

Reasoning prompt: Integrate clinical tempo, lesion anatomy and diagnostic evidence

Slide 4 · PML is viral injury to CNS myelin

JC virus → oligodendrocyte injury → demyelination

JC polyomavirus preferentially infects oligodendrocytes.

Damage to these myelin-forming cells causes central nervous system demyelination.

Neurologic dysfunction reflects the distribution and evolution of white matter injury.

Slide 5 · The disease name encodes its phenotype

PROGRESSIVE

Progressive: Neurologic deficits accumulate rather than follow a single abrupt event.

MULTIFOCAL

Multifocal: Several white matter territories may be involved.

WHITE MATTER

Leukoencephalopathy: The predominant lesion is in cerebral or cerebellar white matter.

Slide 6 · PML is an infectious demyelinating disorder

PML

Autoimmune demyelination

Viral oligodendroglial injury

Immune-mediated myelin injury

Opportunistic host setting

Autoimmune disease setting

Virologic confirmation possible

Virologic confirmation absent

Infection, rather than primary autoimmunity, initiates tissue damage.

Slide 7 · Oligodendrocytes maintain CNS internodes

Oligodendrocyte

Multiple axons / multiple internodes

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 8 · Why myelin loss produces neurologic deficits

Myelin injury

Conduction failure

Network disconnection

Focal dysfunction

Myelin loss reduces effective saltatory conduction along surviving fibers.

Associated axonal injury can further impair information transfer.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 9 · The core pathogenic sequence

Silent infection

Immune impairment

JCV activity in CNS

Myelin destruction

Widespread antecedent JC virus exposure is usually clinically silent.

Immunosuppression permits clinically consequential JC virus activity.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 10 · JC virus is a human polyomavirus

Infection is common; PML is uncommon

The etiologic agent is JC polyomavirus, also termed JCV.

Viral replication within susceptible glial cells causes a cytopathic pattern.

Identification of JCV in tissue or CSF links the demyelinating process to infection.

Slide 11 · Exposure does not mean active disease

JCV exposure

PML

Often asymptomatic

Progressive CNS illness

Serologic evidence may persist

Compatible clinical and MRI syndrome

Does not prove CNS disease

Requires integrated diagnostic assessment

Most people acquire serologic evidence of JC virus exposure without neurologic symptoms.

Slide 12 · Reactivation occurs in a permissive host

Established

PML follows loss of immune control

Pathway remains incompletely resolved

Exact viral latency/entry sequence may vary

Robbins frames PML as JC virus reactivation under immunosuppression.

Slide 13 · The host context is diagnostically powerful

Host context + syndrome + MRI + virology

PML occurs almost exclusively in immunosuppressed patients.

A predisposing immune disorder increases suspicion but is not diagnostic alone.

Atypical host history should prompt broader differential assessment.

Slide 14 · Four risk settings named by Robbins

HIV / AIDS

Cell-mediated immune impairment

Hematologic disease

Lympho- / myeloproliferative illness

Immune-modifying drugs

Chemotherapy and biologics

Granulomatous disease

Host susceptibility context

Slide 15 · HIV and PML: Two distinct CNS processes

PML

HIV encephalitis

JC virus in oligodendrocytes

HIV in microglia/macrophages

Demyelinating plaques

Microglial nodules ± giant cells

Focal deficits dominate

Often diffuse neurocognitive dysfunction

HIV-associated immunodeficiency permits opportunistic JCV disease.

Slide 16 · Hematologic illness can predispose to PML

Chronic lymphoproliferative disease may impair cell-mediated viral control.

Myeloproliferative disease is another context identified by Robbins.

Risk reflects underlying disease and, in some patients, treatment-related immunosuppression.

Slide 17 · Immunosuppressive treatments alter risk

Immune-modifying drug

Altered surveillance

JCV permissiveness

PML risk

Chemotherapy and immune-modifying therapies may permit JCV-associated disease.

Robbins specifically mentions monoclonal antibodies against selected integrins.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 18 · Natalizumab illustrates immune-surveillance disruption

Biologic action

Reduced CNS immune-cell trafficking

Diagnostic consequence

Heightened suspicion when symptoms emerge

Natalizumab targets the α4-integrin pathway and impairs leukocyte trafficking.

Slide 19 · Immune control is the central protective barrier

Effective immune surveillance

Suppressed immune surveillance

Infection generally controlled

Viral replication may cause PML

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 20 · Glial tropism explains lesion identity

JCV glial infection

Nuclear change

Oligodendrocyte loss

Demyelination

JC virus preferentially involves oligodendrocytes in PML.

Infected oligodendrocytes show conspicuous nuclear viral cytopathic effects.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 21 · The lesion is centered in white matter

Cerebral white matter

Cerebellar white matter

Lesion patches

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 22 · Gross pathology: Irregular ill-defined patches

Coalescent pale region

Myelin-stain appearance represented schematically; Lesion contours are not from a specimen

Slide 23 · Multifocal lesions may merge

Preserved myelin

Demyelinated foci

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 24 · Lesion location determines the syndrome

White matter functional connection

Cortical region

White matter tract

Downstream deficit

PML

Lesion

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 25 · Clinical course: Subacute, cumulative deficits

Initial focal sign

Additional deficits

Increasing disability

Clinical evolution—not a quantitative time scale

Slide 26 · Motor pathway involvement

Descending motor pathway

Cortical region

White matter tract

Downstream deficit

PML

Lesion

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 27 · Visual and posterior pathway involvement

Visual information pathway

Occipital cortex

White matter tract

Visual processing deficit

PML

Lesion

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 28 · Cerebellar disease can impair coordination

Cerebral white matter

Cerebellar white matter

Lesion patches

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 29 · Clinical findings are not pathognomonic

Focal weakness, language dysfunction, and visual changes have many causes.

Headache and fever are not characteristic in classical PML.

The differential must integrate tempo, immune state, MRI and laboratory data.

Slide 30 · The MRI question is where myelin is lost

Illustrated abnormal regions

SCHEMATIC — not an MRI; No imaging measurement or lesion burden is implied

Slide 31 · T2-weighted and FLAIR signal

Illustrated abnormal regions

SCHEMATIC — not an MRI; No imaging measurement or lesion burden is implied

Slide 32 · T1 and diffusion provide complementary information

T1 weighted

Reduced signal in affected white matter

Diffusion weighted

Activity may be conspicuous at lesion borders

Affected white matter is commonly hypointense on T1-weighted sequences.

Slide 33 · Enhancement changes the interpretation

Little enhancement

Compatible with classic PML

Marked inflammation

Raises PML-IRIS or another process

Classic PML often shows little contrast enhancement.

Slide 34 · Imaging comparison: Pattern, not a single sign

PML

Toxoplasmosis / lymphoma

Infiltrative white matter abnormality

Often focal mass lesions

Usually limited mass effect

Mass effect may be prominent

JCV-oriented investigation

Different organism/tumor workup

A white matter–predominant, poorly marginated process supports PML in the right host.

Slide 35 · Histologic architecture: Edge and center

Macrophage-rich center

Oligodendrocytes near edge

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 36 · Myelin loss is the defining tissue effect

Preserved myelin

Demyelinated foci

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 37 · Macrophages clear destroyed myelin

Foamy phagocytes

Histomorphologic concept only; Shapes are not microscopy

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 38 · Axonal density can also fall

Myelin loss

Axonal loss

Primary defining lesion

May accompany severe injury

Conduction impaired

Structural pathway loss

Potential remyelination if cells survive

Recovery is more constrained

Reduced numbers of axons within affected lesions.

Slide 39 · Infected oligodendrocytes have enlarged nuclei

Enlarged oligodendroglial nucleus

Histomorphologic concept only; Shapes are not microscopy

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 40 · Nuclear inclusions are an essential clue

Nuclear viral inclusion

Histomorphologic concept only; Shapes are not microscopy

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 41 · Bizarre astrocytes form the third feature

Bizarre astrocytic form

Histomorphologic concept only; Shapes are not microscopy

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 42 · The classic histopathologic triad

Demyelination

Myelin loss / foamy macrophages

Oligodendrocytes

Large nuclei / viral inclusions

Astrocytes

Bizarre forms / hyperchromasia

Interpret the triad together, not as isolated findings

Slide 43 · The advancing edge is diagnostically rich

Macrophage-rich center

Oligodendrocytes near edge

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 44 · Tissue immunohistochemistry adds specificity

Morphology

Triad suggests PML

Virologic tissue test

JCV antigen/DNA demonstrates infection

JCV-associated viral antigens can be demonstrated in infected cell nuclei.

Slide 45 · Granule cell neuron involvement is uncommon

Cerebral white matter

Cerebellar white matter

Lesion patches

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 46 · Differentiate infection from autoimmune plaques

PML

Multiple sclerosis

JC virus–associated

Autoimmune demyelination

Viral nuclear inclusions

No JCV-specific inclusions

Immunosuppression is characteristic

Relapses and dissemination patterns are relevant

Both PML and multiple sclerosis can produce focal myelin loss.

Slide 47 · A small biopsy has sampling limitations

Macrophage-rich center

Oligodendrocytes near edge

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 48 · First: Establish a coherent clinical hypothesis

Immune history

Neurologic tempo

MRI distribution

Integrated suspicion

Document host immune impairment and treatment exposures.

Map the evolving deficits to the anatomic distribution of MRI lesions.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 49 · CSF JC-virus PCR supports diagnosis

Compatible syndrome

Progressive focal deficits + MRI lesions

JCV DNA detected in CSF

Supports a clinical diagnosis of PML

CSF detection of JCV DNA is a key noninvasive confirmatory investigation.

Slide 50 · A negative CSF result does not exclude PML

High suspicion

Negative JCV PCR

Reconsider / repeat

Biopsy if needed

Assay sensitivity varies with viral burden, treatment and laboratory methods.

Negative testing in a strongly suspicious case warrants reassessment.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 51 · Biopsy-based diagnosis follows another route

Demyelination

Myelin loss / foamy macrophages

Oligodendrocytes

Large nuclei / viral inclusions

Astrocytes

Bizarre forms / hyperchromasia

Histologic triad + JCV detection in tissue

Slide 52 · AAN diagnostic framework uses two routes

Progressive deficit + PML-like MRI

Demyelinating biopsy specimen

CSF JCV PCR

Histologic triad + JCV assay

Clinical diagnostic route

Tissue diagnostic route

Concordance across clinical, imaging and virologic domains is essential

Slide 53 · A practical diagnostic workflow

Progressive deficit + PML-like MRI

Demyelinating biopsy specimen

CSF JCV PCR

Histologic triad + JCV assay

Clinical diagnostic route

Tissue diagnostic route

Concordance across clinical, imaging and virologic domains is essential

Slide 54 · PML versus HIV encephalitis

PML

HIV encephalitis

JCV-infected oligodendrocytes

HIV-associated microglia

Large focal white matter plaques

Microglial nodules / giant cells

Typically focal deficits

Often cognitive dysfunction

PML targets oligodendrocytes and produces demyelinating lesions.

Slide 55 · PML versus focal opportunistic masses

PML

Toxoplasmosis

CNS lymphoma

Demyelination

Infection / necrosis

Neoplastic infiltrate

White matter–predominant

Often ring-enhancing

Often enhancing mass

CSF JCV / biopsy

Pathogen workup

Tissue / lymphoma workup

Toxoplasmosis can produce necrotizing abscess-like lesions.

Slide 56 · PML versus inflammatory demyelination

Observation

Inference

Foamy macrophages

Shared, nonspecific finding

JCV-positive glial nuclei

Supports viral demyelination

Atypical astrocytes alone

Insufficient; Avoid glioma overcall

A diagnosis of multiple sclerosis cannot explain JCV-positive oligodendrocytes.

Slide 57 · Immune reconstitution can intensify inflammation

Restoring immunity

Inflammatory lesion response

Potential paradoxical worsening after immune recovery

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 58 · Recognizing PML-associated IRIS

Uncontrolled PML

Ongoing virus-associated injury

PML-associated IRIS

Inflammation after immune recovery

Clinical deterioration may accompany new enhancement, edema or mass effect.

Slide 59 · Therapeutic principle: Restore antiviral immunity

Recognize PML

Reverse immune deficit

Monitor neurologic course

Assess IRIS

No reliably effective direct anti-JCV treatment is established.

The principal intervention is reversing the underlying immunosuppression when feasible.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 60 · HIV-associated PML: Effective ART is central

Initiate antiretroviral therapy promptly when HIV-associated PML occurs without effective ART.

Optimize virologic suppression if current ART is failing.

Do not discontinue ART solely because PML-associated IRIS develops.

Slide 61 · Drug-associated PML requires specialist coordination

Assess the implicated immunosuppressant and feasibility of withdrawing or modifying it.

Management depends on the indication, persistence and pharmacology of the agent.

Neurology, infectious disease and the treating specialty should coordinate care.

Slide 62 · No direct antiviral has proved consistently effective

No established JCV-directed antiviral standard

Trials of several antiviral or repurposed agents have not established routine benefit.

Experimental immunotherapies should not be presented as accepted standards.

Immune restoration remains the evidence-based therapeutic foundation.

Slide 63 · Monitoring follows clinical progression

Baseline

After intervention

Reassessment

Clinical evolution—not a quantitative time scale

Slide 64 · Prognosis is tied to immune recovery and injury

IMMUNE RECOVERY

The extent and location of damage influence functional consequences.

LESION BURDEN

The capacity to restore immune control is a major determinant of outcome.

AXONAL DAMAGE

Persistent neurologic deficits may reflect accumulated axonal and myelin injury.

Slide 65 · Case application: Evaluating a new deficit

Hypothetical case; No real patient image or data.

Teaching scenario: A patient on immune-modifying therapy develops progressive aphasia.

MRI shows an enlarging asymmetric subcortical white matter abnormality.

What is the next diagnostic hypothesis and how should it be investigated?

Reasoning prompt: Integrate clinical tempo, lesion anatomy and diagnostic evidence

Slide 66 · Case reasoning: Triangulate the evidence

Clinical course

Exposure history

MRI anatomy

JCV testing

An immunosuppressive exposure and progressive focal deficit increase PML suspicion.

MRI white matter involvement makes a demyelinating process plausible.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 67 · Case application: Reading a biopsy

Teaching scenario: Tissue shows pallor of myelin, foamy macrophages and enlarged glial nuclei.

At the advancing margin, inclusion-bearing oligodendrocytes and bizarre astrocytes are seen.

Which tissue-based test most directly confirms the etiologic diagnosis?

Reasoning prompt: Integrate clinical tempo, lesion anatomy and diagnostic evidence

Slide 68 · Case reasoning: Confirm JC virus

Demyelination

Myelin loss / foamy macrophages

Oligodendrocytes

Large nuclei / viral inclusions

Astrocytes

Bizarre forms / hyperchromasia

Histologic triad + JCV detection in tissue

Slide 69 · Integrated pathology summary

Immune deficit

JCV cytopathy

Demyelination

Focal deficits

JC virus preferentially damages oligodendrocytes during severe immune impairment.

Irregular subcortical white matter lesions contain central macrophages and marginal infected glia.

SCHEMATIC — conceptual illustration, not a clinical or histologic specimen

Slide 70 · Selected references

Robbins, Cotran & Kumar

Pathologic Basis of Disease, 11th ed. (2026), Chapter 28; PML pp. 1153–1154.

AAN Neuroinfectious Disease Section

PML diagnostic criteria: consensus statement. Neurology. 2013;80:1430–1438.

NIH Adult & Adolescent OI Guidelines

Progressive Multifocal Leukoencephalopathy/JC Virus; updated 2022, reviewed 2026.

Image / schematic integrity

All diagrams in this deck are original editable conceptual schematics; no specimen images reproduced.