Parkinson Disease

Slide 1 · Parkinson Disease

Neurodegeneration · molecular mechanisms · morphology · clinical correlation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Teaching objectives

Explain how nigrostriatal dopamine loss produces parkinsonism.

Compare major genetic and cellular mechanisms implicated in PD.

Recognize substantia nigra depigmentation, Lewy bodies, and Lewy neurites.

Connect pathology to clinical features, progression, and treatment limits.

Slide 3 · Parkinson disease is more than parkinsonism

Disease

Parkinson disease is a neurodegenerative disease.

Loss of substantia nigra dopaminergic neurons causes the motor syndrome.

Pathology also affects nuclei beyond the nigrostriatal system.

Syndrome

Parkinsonism describes a recognizable movement syndrome.

It may follow PD, dopamine-receptor antagonism, toxins, or other disorders.

A syndrome alone does not identify the underlying disease.

Slide 4 · The central clinicopathologic pathway

Nigral degeneration

Loss of dopaminergic neurons

Striatal dopamine loss

Reduced nigrostriatal input

Hypokinetic syndrome

Bradykinesia, rigidity, tremor

The pathway explains the dominant motor abnormalities. • Other involved brain regions help explain nonmotor and cognitive consequences.

Slide 5 · The nigrostriatal circuit

Relatively preserved

Substantia

Nigra

Striatum

More nigral neurons → dopamine input

Degenerated in PD

Substantia

Nigra

Striatum

Fewer neurons → less dopamine

Loss of neurons in the substantia nigra reduces dopaminergic innervation of the striatum.

Slide 6 · Motor manifestations form a recognizable constellation

Movement

Slowing of voluntary movement

Tone / rhythm

Rigidity and pill-rolling tremor

Posture / gait

Stooped posture and festination

Face

Diminished facial expression

Slide 7 · Bradykinesia: Slowing of movement

Bradykinesia denotes abnormally slow voluntary movement.

It is one component of the core clinical triad used.

It reflects dysfunction of the nigrostriatal dopaminergic system.

The clinical finding is not, by itself, specific for PD.

Slide 8 · Festinating gait

Forward lean

Stooped posture

Shortening steps

Progressively shorter steps

Festination

Increasingly rapid steps

Festination as progressively shortened, accelerated steps with forward leaning. • A characteristic gait supports the syndrome, not necessarily a unique cause.

Slide 9 · Parkinsonism has multiple etiologies

Parkinson disease

Neurodegeneration of nigral dopaminergic neurons.

Typical Lewy pathology in many affected neurons.

Progression may involve brainstem, limbic system, and cortex.

Other causes

Dopaminergic antagonists may induce symptoms.

Some toxins selectively injure the dopamine system.

Other neurodegenerative disorders can include parkinsonism.

Slide 10 · Dopamine antagonism can mimic PD

Dopamine signaling

Blocked pharmacologically

Motor-circuit function

Reduced dopaminergic effect

Parkinsonism

Clinically similar syndrome

Textbook distinction: A drug-induced phenotype is not equivalent to established idiopathic PD. • Review exposure history when evaluating parkinsonism.

Slide 11 · MPTP: A selective dopaminergic neurotoxin

MPTP is 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

An illicitly synthesized meperidine contaminant was linked to acute parkinsonism.

Exposure can destroy substantia nigra neurons.

The resulting motor syndrome illustrates vulnerability of the dopaminergic system.

Slide 12 · Why MPTP matters experimentally

Defined toxin exposure

MPTP

Selective injury

Nigral dopaminergic neurons

Model phenotype

Parkinsonian motor signs

MPTP exposure provides an experimental model of nigrostriatal injury. • Animal models of this type have been used to test therapies.

Slide 13 · Pesticide exposure is an epidemiologic signal

Epidemiologic evidence associating pesticide exposure with increased PD risk.

An association does not establish a specific causal mechanism for every exposure.

Environmental susceptibility and inherited susceptibility are distinct questions.

The observation supports investigation of environmental contributions.

Slide 14 · Protective associations are not treatment advice

Source-reported associations

Caffeine exposure appears protective in epidemiologic studies.

Nicotine exposure also appears protective in epidemiologic observations.

Interpretive limit

Observational associations do not establish prevention or treatment efficacy.

The textbook description is not a recommendation to use nicotine.

Slide 15 · Most PD is sporadic

Sporadic disease is the predominant presentation.

Familial cases have identified genes relevant to pathogenic mechanisms.

Mutations can illuminate protein aggregation, mitochondrial quality control, and lysosomal biology.

Mechanistic relevance does not imply every sporadic case carries the same mutation.

Slide 16 · Three converging mechanisms

Protein homeostasis

α-synuclein accumulation and oligomer toxicity

Mitochondrial integrity

Stress responses and defective mitophagy

Lysosomal clearance

Disruption of autophagy–lysosome function

Signaling regulation

LRRK2 kinase and Rab-protein phosphorylation

Slide 17 · SNCA encodes α-synuclein

SNCA encodes α-synuclein, a lipid-binding protein abundant at synapses.

α-Synuclein is a major molecular component of Lewy bodies.

Inherited SNCA mutations established a direct genetic link to PD.

This relationship connects a synaptic protein to neuronal aggregate pathology.

Slide 18 · SNCA pathogenic alterations

Sequence-level changes

Rare inherited point mutations affect SNCA.

Certain mutations cause autosomal dominant PD.

Copy-number / dosage

Amplification of the SNCA-containing region on chromosome 4q21 is described.

Increased gene dosage is another route to α-synuclein-associated PD.

Slide 19 · Aggregation is not a single molecular state

α-Synuclein

Normally enriched at synapses

Misfolded aggregates

Including small oligomers

Lewy pathology

Larger cytoplasmic inclusions

The source specifically points to small α-synuclein oligomers as apparently most toxic to neurons. • Visible Lewy bodies and the implicated toxic molecular species should not be conflated.

Slide 20 · A proposed neuron-to-neuron spread mechanism

Donor neuron

Aggregate release

Extracellular transfer

Potential uptake by neighbor

Recipient neuron

Intracellular aggregation

A prion-like pattern of propagation is suggested by experimental observations. • Present this as evidence supporting a model—not proof that all PD follows an identical route.

Slide 21 · The anatomic progression model

Lower brainstem / medulla

Early described Lewy pathology

Other brainstem regions

Ascending involvement

Limbic structures

More widespread aggregate distribution

Neocortex

Late potential cortical involvement

Schematic of a described pattern of aggregate distribution; Not a mandatory staging rule for every patient.

Slide 22 · Anatomic sequence and causality are different

Observed / described

Aggregates may appear in medulla and contiguous ascending regions.

Lewy bodies and neurites can occur in multiple neuronal populations.

Interpretation

Intercellular propagation is a plausible explanation.

The extent to which spreading itself causes degeneration is not fully resolved.

Slide 23 · Mitochondrial dysfunction in PD

Inherited PD genes implicate mitochondrial homeostasis.

DJ-1, PINK1, and Parkin are linked to autosomal recessive PD.

Normal mitochondrial quality control limits persistence of damaged organelles.

Defects in this machinery offer a route to neuronal injury.

Slide 24 · DJ-1 contributes to the stress response

Oxidative stress

Cellular injury context

DJ-1 redistribution

Can relocate to mitochondria

Cytoprotection

Mitochondrial protective role

DJ-1 also has other cellular roles, including transcriptional regulation. • Pathogenic alteration of DJ-1 is one genetic link between oxidative stress responses and PD.

Slide 25 · PINK1 identifies dysfunctional mitochondria

Damaged mitochondrion

Quality-control target

PINK1 kinase

Accumulation at outer membrane

Parkin recruitment

Pathway activation

PINK1 localizes to the outer membrane of dysfunctional mitochondria. • It recruits and phosphorylates Parkin, leading toward mitophagy.

Slide 26 · Parkin is an E3 ubiquitin ligase

PINK1-dependent phosphorylation activates Parkin.

Parkin functions as an E3 ubiquitin ligase.

Activated Parkin ubiquitinates mitochondrial proteins.

Those tags help identify damaged mitochondria for autophagic clearance.

Slide 27 · The PINK1–Parkin mitophagy pathway

Dysfunctional mitochondrion

PINK1 signaling

Parkin activation

Ubiquitination of targets

Mitophagy

Autophagic removal

Quality control

Clearance of damaged organelle

Mitophagy is selective autophagic degradation of mitochondria. • The pathway normally prevents persistence of dysfunctional mitochondria.

Slide 28 · PINK1 or Parkin defects disrupt clearance

Functioning pathway

PINK1 senses a dysfunctional mitochondrion.

Parkin is recruited and activated.

Ubiquitinated organelle proteins support mitophagy.

Genetic defect

PINK1 or Parkin mutation impairs the pathway.

Damaged mitochondria are less effectively cleared.

Mitochondrial dysfunction can persist and contribute to injury.

Slide 29 · Complex I is reduced in sporadic PD brains

Reduced mitochondrial complex I levels in brains with sporadic PD.

Complex I participates in oxidative phosphorylation.

This observation links mitochondrial abnormalities with nonfamilial disease.

An observed reduction alone does not specify which molecular defect initiated the disease.

Slide 30 · GBA1 changes PD susceptibility

GBA1 encodes the lysosomal enzyme glucocerebrosidase.

Heterozygous GBA1 mutations are an important genetic risk factor for PD.

The textbook attributes approximately 5% of PD cases to this genetic association.

Biallelic pathogenic GBA1 variants can cause Gaucher disease.

Slide 31 · Lysosomal function connects metabolism to PD

GBA1 / enzyme

Glucocerebrosidase

Lysosomal pathway

Degradative homeostasis

PD susceptibility

Disturbed proteostasis

The genetic link implicates the autophagy–lysosome pathway. • The precise route from risk variant to selective neuronal injury is multifactorial.

Slide 32 · Candidate consequences of GBA1 dysfunction

α-Synuclein

Abnormal metabolism / clearance

Autophagy

Impaired degradative flux

Proteostasis

Unfolded protein response activation

Inflammation

Increased inflammatory signaling

Slide 33 · LRRK2 encodes a cytoplasmic kinase

LRRK2 mutations can cause autosomal dominant PD.

Certain pathogenic variants increase LRRK2 kinase activity.

LRRK2 variants also occur in apparently sporadic late-onset disease.

The pathway does not reduce to α-synuclein accumulation alone.

Slide 34 · LRRK2 and Rab phosphorylation

Pathogenic LRRK2

Increased kinase activity

Rab proteins

Excess phosphorylation

Cellular dysfunction

Mechanistic link under study

Robbins implicates small GTPase Rab proteins as relevant substrates. • The subsequent connection to α-synuclein accumulation and neuron loss remains incompletely explained.

Slide 35 · Separate LRRK2 evidence from open questions

Established in source

Some pathogenic LRRK2 variants elevate kinase activity.

Rab hyperphosphorylation is implicated in PD pathogenesis.

Not yet resolved

The exact causal route from Rab phosphorylation to degeneration is not elucidated.

Do not diagram a fully proven linear pathway to neuron death.

Slide 36 · Genetic routes are not interchangeable

Gene / factor

Inheritance or association

Key mechanistic link

SNCA

Autosomal dominant (rare)

α-Synuclein aggregation

PINK1 / PRKN

Autosomal recessive

Mitochondrial mitophagy

PARK7 (DJ-1)

Autosomal recessive

Stress / mitochondria

GBA1

Heterozygous risk factor

Autophagy–lysosome

LRRK2

Autosomal dominant

Kinase / Rab signaling

Slide 37 · Different genes converge on neuronal vulnerability

Proteostatic stress

α-Synuclein aggregation

Organelle injury

Mitochondria / lysosomes

Neuronal loss

Substantia nigra and beyond

Genetic pathways offer complementary, not mutually exclusive, explanations. • The final shared histologic effect includes neuronal loss and gliosis.

Slide 38 · Gross pathology: Substantia nigra pallor

Reference appearance

Numerous pigmented neuronal profiles

PD — depigmentation

Fewer pigmented neuronal profiles

Macroscopic depigmentation reflects loss of neuromelanin-containing catecholaminergic neurons.

Conceptual schematic; Not anatomic gross specimens.

Slide 39 · The locus ceruleus may also be pale

The locus ceruleus contains pigmented catecholaminergic neurons.

Loss of these neurons produces pallor in PD.

The finding demonstrates pathologic involvement outside the substantia nigra.

Gross pallor and microscopic neuronal depletion are causally linked.

Slide 40 · What a Lewy body is

Dense eosinophilic core

Pale peripheral halo

Pigmented neuron

Rounded to elongated cytoplasmic eosinophilic inclusion in a surviving neuron; Often a dense center with a pale halo.

Schematic — not a histologic specimen

Slide 41 · Lewy-body components and architecture

Molecular content

α-Synuclein-rich filaments

Central core

Densely packed filaments

Peripheral rim

Looser filament arrangement

The ultrastructural description explains the dense core and lighter rim seen in many inclusions. • Morphologic inclusions identify a lesion, not the full molecular mechanism of toxicity.

Slide 42 · Lewy bodies occur in surviving neurons

One neuron may contain a single or multiple Lewy bodies.

Inclusions are cytoplasmic rather than nuclear.

They may be round or elongated and intensely eosinophilic.

Residual pigmented neurons in affected nuclei are important sites to examine.

Slide 43 · Lewy neurites are abnormal neuronal processes

Aggregated α-synuclein within a dystrophic process

Lewy neurites are dystrophic processes containing aggregated α-synuclein.

Schematic — not a histologic specimen

Slide 44 · The distribution of Lewy pathology is broad

Substantia nigra

Residual dopaminergic neurons

Locus ceruleus

Additional brainstem nucleus

Dorsal motor nucleus of vagus

Another brainstem site

Basal nucleus of Meynert

Cholinergic neurons

Slide 45 · Neuronal loss is accompanied by gliosis

Neuron injury / loss

Affected anatomic nuclei

Glial response

Reactive gliosis

Tissue correlate

Reduced neuron population

Gliosis often accompanies areas of neuronal depletion. • Neither gliosis nor Lewy pathology should be interpreted without anatomic context.

Slide 46 · The clinical diagnosis uses a classic triad

Bradykinesia

Slow movement

Rigidity

Increased resistance to movement

Tremor

Classically pill-rolling

Slide 47 · Clinical context helps distinguish causes

Parkinsonian signs

Bradykinesia ± other signs

Etiologic assessment

Toxic and known causes

PD as a diagnosis

Clinical interpretation

The Robbins text emphasizes the classic triad in the absence of a known toxic or other underlying etiology. • A motor phenotype alone does not prove a specific neuropathology.

Slide 48 · Pathologic signature is not a bedside test

At the bedside

Movement slowing, rigidity, tremor, posture and gait.

Clinical history helps identify drug or toxin exposure.

In nervous tissue

Nigral cell loss, depigmentation and gliosis.

Lewy bodies / neurites support an α-synuclein proteinopathy.

Slide 49 · PD pathology can extend beyond motor nuclei

Lower brainstem

Early described involvement

Substantia nigra

Motor degeneration becomes prominent

Limbic / cortical sites

Later possible clinical effects

Conceptual sequence drawn from the textbook; Clinical patterns may vary.

Slide 50 · Cortical involvement can impair cognition

PD is not necessarily confined to the basal ganglia.

Neocortical involvement is associated with cognitive impairment.

Lewy pathology may extend into cortical and limbic neurons.

PD and dementia with Lewy bodies occupy a related α-synuclein disease spectrum.

Slide 51 · Why L-DOPA can improve motor symptoms

Nigral neuron loss

Striatal dopamine deficiency

L-DOPA treatment

Immediate dopamine precursor

Motor response

Partial replacement of deficient signaling

Motor impairment severity correlates with dopamine deficiency. • L-DOPA can improve motor symptoms, especially early in the disease.

Slide 52 · Symptomatic improvement is not neuroprotection

What L-DOPA addresses

Replaces a biochemical deficit in dopamine signaling.

Can initially improve the motor phenotype.

What it does not address

Does not arrest ongoing neurodegenerative progression.

Does not directly eliminate all widespread nonmotor pathology.

Slide 53 · Why therapy becomes less effective over time

PD continues to progress despite dopamine replacement.

The affected neuronal systems are more extensive than the nigrostriatal pathway.

Increasing difficulty managing motor symptoms over time.

Drug response is not equivalent to reversal of the disease process.

Slide 54 · Deep brain stimulation is symptomatic therapy

Deep brain stimulation can treat selected motor symptoms of PD.

It represents a therapeutic approach distinct from dopamine precursor replacement.

Benefit for motor manifestations.

The text does not establish that stimulation halts the underlying neurodegeneration.

Slide 55 · PD and dementia with Lewy bodies overlap

PD-centered presentation

Motor parkinsonism predominates clinically.

Cognitive decline can emerge as cortical disease develops.

Nigral loss and Lewy pathology are prominent.

DLB-centered presentation

Cognitive manifestations may be the presenting concern.

Widespread cortical and brainstem Lewy pathology can occur.

Both belong to an α-synuclein disease spectrum.

Slide 56 · Atypical parkinsonian syndromes are not PD

Parkinson disease

Classic nigrostriatal motor phenotype.

Often initially responsive to L-DOPA.

Lewy body α-synuclein pathology in typical cases.

Atypical parkinsonism

Additional neurologic signs are prominent.

In general, little response to L-DOPA.

PSP/CBD are tauopathies; MSA is a glial synucleinopathy.

Slide 57 · Pathology separates major Parkinson-plus disorders

Syndrome

Prominent clinical feature

Main pathologic protein / site

PSP

Eye movement difficulty; early falls

Tau, neuronal and glial

CBD

Asymmetric motor disturbance; apraxia

Tau, especially cortex

MSA

Autonomic dysfunction / ataxia

α-Synuclein, oligodendroglia

Typical PD

Bradykinesia, tremor, rigidity

α-Synuclein, neuronal Lewy bodies

Slide 58 · Case: Progressive hypokinetic movement syndrome

Clinical vignette

An adult develops progressively slowed movements, reduced facial expression, rigidity, a pill-rolling tremor, and short accelerating steps.

Which disrupted neural system most directly explains the motor phenotype?

Reasoning: The substantia nigra-to-striatum dopaminergic system; Loss of nigral neurons reduces striatal dopamine.

Slide 59 · Case: An unexpected etiologic clue

Clinical vignette

An individual develops new rigidity and bradykinesia after exposure to a dopamine-receptor antagonist.

Why is the parkinsonian phenotype insufficient to establish idiopathic PD?

Reasoning: Dopamine antagonism can produce a similar syndrome without demonstrating primary idiopathic neurodegeneration.

Slide 60 · Case: A molecular mechanism of inherited PD

Clinical vignette

A familial PD-associated variant impairs PINK1-dependent recruitment and activation of Parkin at damaged mitochondria.

Which cellular quality-control process is most directly affected?

Reasoning: Mitophagy: Ubiquitin-dependent targeting and autophagic clearance of dysfunctional mitochondria.

Slide 61 · Integrating genotype, morphology, and clinical signs

Biologic level

Example

Consequence

Gene / protein

SNCA → α-synuclein

Aggregate pathology

Cellular system

PINK1 / Parkin

Mitophagy impairment

Gross / tissue

Nigral neuron loss

Pallor + gliosis

Circuit / function

Striatal dopamine depletion

Hypokinetic motor signs

Progression

Extra-nigral pathology

Possible cognitive impairment

Slide 62 · The unifying clinicopathologic model

Inherited / sporadic influences

Protein and organelle dysfunction

Neurodegeneration

Nigra + extra-nigral nuclei

Clinical consequences

Motor syndrome; Later cognitive effects

Lewy bodies are hallmark lesions in typical PD, but molecular and anatomic processes are broader. • Treatments improve symptoms without abolishing the underlying progression.

Slide 63 · Essential morphology to recognize

Gross specimen

Pale substantia nigra and locus ceruleus

H&E pattern

Eosinophilic cytoplasmic Lewy inclusion with pale halo

Proteinopathy

α-Synuclein aggregates in Lewy bodies / neurites

Background tissue

Neuronal depletion with gliosis

Slide 64 · What the source establishes—and what remains open

Supported by Robbins

Loss of nigral dopaminergic neurons explains major motor signs.

SNCA, mitophagy, lysosome and LRRK2 genes illuminate disease biology.

Typical morphology includes neuronal loss, pallor and Lewy pathology.

Mechanistic uncertainty

Relative contributions of individual pathways to every sporadic case.

A fully proven neuron-to-neuron propagation mechanism.

The exact pathway from abnormal LRRK2–Rab signaling to neuron death.

Slide 65 · Primary reading

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. Chapter 28: The Central Nervous System; “Parkinson Disease.”

Related textbook context: “Dementia with Lewy Bodies” and “Atypical Parkinsonian Syndromes.”

Teaching diagrams in this lecture are original, editable schematics—not clinical photographs or histologic specimens.