Rheumatoid Arthritis (Lecture 2)

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Lecture topics

RA is a chronic autoimmune synovitis
ACPA and RF are complementary—not interchangeable
TNF is a central inflammatory amplifier
Inflammatory infiltrates are mixed and chronic
Joint remodeling represents a temporal sequence
MCP and PIP joint disease is characteristic
Therapy targets inflammation and structural injury
Principal reference and image-use statement

Slide index & full transcript (69 slides)

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Slide 1 · Rheumatoid Arthritis

Autoimmune synovitis • pannus • joint destruction

Immune mechanisms

Morphologic changes

Clinical correlation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives: Mechanistic and diagnostic reasoning

Explain how autoimmunity produces chronic synovial inflammation.

Connect CD4⁺ T-cell cytokines and autoantibodies to tissue injury.

Recognize pannus, erosions, nodules, and possible ankylosis.

Use distribution, serology, and imaging to distinguish RA from OA.

LECTURE FRAMEWORK

Autoimmune initiation

Synovial inflammation

Tissue destruction

Clinicopathologic interpretation

Slide 3 · RA is a chronic autoimmune synovitis

RA principally targets synovial joints, rather than beginning as primary cartilage degeneration.

The synovitis is nonsuppurative, proliferative, and inflammatory.

Persistent inflammation can destroy articular cartilage and adjacent bone.

Disease may culminate in fibrous and subsequently bony ankylosis.

DEFINITION

Joint section — schematic

Subchondral bone

Synovial expansion

Slide 4 · The central injury model links immunity to erosions

Loss of immune tolerance permits reactions to self-antigens associated with joints.

Activated lymphocytes and macrophages establish an inflammatory synovial milieu.

Synovial proliferation and protease release damage cartilage.

Osteoclast activity produces periarticular bone erosion.

CAUSAL SEQUENCE

Loss of tolerance

Inflammatory synovitis

Pannus + proteases

Cartilage and bone erosion

Slide 5 · Epidemiologic features

Reported US prevalence: Approximately 0.25%–1%.

Incidence peaks in the third to fourth decades.

Females are affected approximately three times as often as males.

These are broad textbook population descriptors, not clinical diagnostic criteria.

SOURCE-REPORTED EPIDEMIOLOGY

US prevalence: ~0.25%–1%

Peak incidence: 3rd–4th decades

Female:male ≈ 3:1

Slide 6 · RA has articular and extraarticular expression

The small joints of hands and feet are common initial sites.

Inflammation may also involve skin, heart, vessels, and lungs.

These systemic manifestations reflect RA as an autoimmune disorder.

Extraarticular findings can overlap with those of other systemic autoimmune diseases.

DISEASE SCOPE

Systemic autoimmunity

Synovium → joint damage

Skin, lung, heart, vessels

Articular + extraarticular disease

Slide 7 · RA is primarily an immune-mediated joint disease

CD4⁺ helper T cells reacting to joint-associated antigens initiate the proposed response.

A number of candidate antigens have been suggested; No single trigger is established here.

Both cellular immunity and humoral autoimmunity contribute to the pathogenic model.

The damaged target tissue is inflamed synovium with adjacent cartilage and bone.

IMMUNE INITIATION

Joint-associated antigen

CD4⁺ T-cell response

Inflammatory mediators

Synovitis and tissue injury

Slide 8 · Candidate antigens include modified self-proteins

Collagen and chemically modified peptides have been proposed as joint antigenic targets.

Citrullination modifies arginine residues within proteins.

Modified epitopes may become targets of autoantibody and T-cell responses.

The initiating antigen(s) remain incompletely defined.

ANTIGEN MODIFICATION

Native self-protein

Arginine → citrulline

Modified epitope

Potential autoreactivity

Slide 9 · Citrullination creates antigenic epitopes

Citrullinated proteins contain post-translationally modified arginine residues.

Examples of targets described include fibrinogen, type II collagen, α-enolase, and vimentin.

Antibodies to citrullinated peptides are termed ACPAs.

Epitope modification is implicated in immune recognition; It is not proof of one universal initiating site.

SOURCE-LISTED AUTOANTIGENS

Fibrinogen

Type II collagen

α-Enolase

Vimentin

Slide 10 · ACPA bridges autoimmunity and diagnosis

Anti-citrullinated peptide antibody (ACPA) detects humoral autoreactivity.

Serum ACPA detection in up to 70% of RA patients.

ACPA is a useful diagnostic marker, not a standalone test that confirms or excludes RA.

Some evidence links ACPA, with citrulline-reactive T cells, to persistence and severity.

AUTOANTIBODY INTERPRETATION

Citrullinated self-proteins

ACPA production

Serum antibody detection

Support for RA diagnosis

Slide 11 · Rheumatoid factor is directed against IgG

Rheumatoid factors include IgM and IgA autoantibodies binding the Fc region of IgG.

RF in approximately 80% of people with RA.

RF may form or deposit as immune complexes within joints.

RF is neither universally present in RA nor specific to RA alone.

RF TARGET AND CONSEQUENCE

IgG Fc region

Binding by RF (IgM/IgA)

Immune complexes

Potential inflammatory contribution

Slide 12 · ACPA and RF are complementary—not interchangeable

Feature

ACPA

Rheumatoid factor

Antigen

Citrullinated peptides

Fc region of IgG

Textbook frequency

Up to 70% of RA

About 80% of RA

Clinical role

Diagnostic support

Specificity caveat

Cannot stand alone

May occur without RA

Proposed damage

May influence persistence

Immune complexes possible

Slide 13 · Genetic susceptibility is substantial

Inherited variation contributes to developing and sustaining RA.

The textbook estimates that about half of susceptibility is inherited.

Susceptibility is polygenic and interacts with environmental exposures.

Genetic predisposition does not by itself establish the disease.

GENE–ENVIRONMENT MODEL

RA susceptibility

Inherited factors

Environmental factors

Loss of tolerance / clinical disease

Slide 14 · HLA-DR4 is linked to ACPA-positive disease

The HLA-DR4 allele is associated particularly with ACPA-positive RA.

Class II HLA molecules participate in antigen presentation to CD4⁺ T cells.

Presentation of citrullinated peptides offers a plausible link to autoreactive responses.

HLA association is not sufficient for a clinical diagnosis.

HLA ASSOCIATION

HLA class II susceptibility

Peptide presentation

CD4⁺ T-cell engagement

Autoreactive response

Slide 15 · Molecular mimicry remains a proposed mechanism

A peptide epitope on citrullinated proteins may resemble microbial epitopes.

Certain epitopes may be presented by HLA-DR4.

Such cross-reactivity could promote activation of autoreactive lymphocytes.

The source presents this as a hypothesis, not an established universal trigger.

MECHANISTIC HYPOTHESIS

Similar epitope patterns

Microbial peptide

Citrullinated self-peptide

Potential T-cell cross-reactivity

Slide 16 · Environment may promote autoimmune priming

Environmental contributors are suspected but remain incompletely defined.

Smoking and infection, including periodontitis, are proposed influences.

A suggested connection is increased citrullination of self-proteins.

Do not interpret an association as proof that one exposure causes every case.

PROPOSED TRIGGERS

Smoking / infection / periodontitis

Possible citrullination

Novel antigenic epitopes

Autoimmune activation?

Slide 17 · Failure of tolerance precedes inflammatory injury

Self-reactive lymphocytes persist or become inappropriately activated.

Recognition of modified or other joint antigens sustains the response.

Leukocytes enter the synovial tissue, amplifying inflammation.

Synovial and bone-resorbing cells then mediate structural damage.

IMMUNOLOGIC SEQUENCE

Immune tolerance failure

T-/B-cell activation

Cell recruitment to synovium

Pannus and erosions

Slide 18 · T cells and B cells form an interacting network

CD4⁺ helper T cells can orchestrate local inflammatory responses.

B cells and plasma cells provide autoantibodies and lymphoid infiltrates.

Macrophages release cytokines important in synovitis.

Inflamed synovial cells, chondrocytes, and osteoclasts execute tissue injury.

IMMUNE CELL NETWORK

Autoreactive lymphocytes

T cells → cytokines

B cells → antibodies

Macrophage / synovial activation

Slide 19 · Th1 cells activate inflammatory effector cells

Th1 is a CD4⁺ T-helper subset implicated in RA.

Th1-derived interferon-γ (IFN-γ) activates macrophages.

IFN-γ can stimulate resident synovial cells.

Macrophage and stromal responses support persistent tissue inflammation.

TH1 ARM

Th1 CD4⁺ cell

IFN-γ

Macrophage + synovial activation

Inflammation

Slide 20 · Th17-derived IL-17 recruits leukocytes

Th17 cells are another implicated CD4⁺ helper population.

IL-17 promotes recruitment of neutrophils and monocytes.

Recruited inflammatory cells reinforce synovitis.

This differs from the predominantly macrophage-activating action of Th1-derived IFN-γ.

TH17 ARM

Th17 lymphocyte

IL-17

Neutrophil + monocyte recruitment

Amplified synovitis

Slide 21 · Macrophage cytokines drive synovial destruction

Macrophages secrete TNF, IL-1, and IL-6 within the inflammatory network.

These mediators recruit and activate leukocytes.

They induce synovial cells to release matrix-degrading proteases.

Enzymatic damage erodes hyaline articular cartilage.

CYTOKINE–MATRIX AXIS

Activated macrophage

TNF / IL-1 / IL-6

Synovial protease production

Cartilage destruction

Slide 22 · TNF is a central inflammatory amplifier

TNF participates in leukocyte recruitment and tissue inflammation.

Its activity is implicated in cartilage and joint damage.

Clinical benefit from TNF antagonists supports its pathogenic importance.

The response to treatment does not imply that TNF is the sole disease driver.

TNF NETWORK

TNF signaling

Leukocyte recruitment

Synovial activation

Ongoing destructive inflammation

Slide 23 · Proteases link synovitis to cartilage erosion

Inflammatory cytokines stimulate synovial cells to make proteases.

These enzymes degrade the extracellular matrix of hyaline cartilage.

Cartilage loss narrows the functional articulating space.

Inflammation therefore directly changes load-bearing joint architecture.

PROTEOLYTIC INJURY

Cytokine-exposed synovium

Matrix-degrading proteases

Cartilage matrix loss

Progressive joint damage

Slide 24 · RANKL promotes osteoclastic bone resorption

Activated T cells can express receptor activator of NF-κB ligand (RANKL).

RANKL stimulates osteoclast formation or activation.

Activated osteoclasts resorb bone adjacent to inflamed synovium.

This provides a cellular mechanism for periarticular erosions.

BONE RESORPTION AXIS

Activated T cell

RANKL expression

Osteoclast activation

Periarticular bone erosion

Slide 25 · Antibodies may participate in joint inflammation

Synovial B cells and plasma cells can secrete autoantibodies.

RF-containing complexes may accumulate in joint tissues.

The source considers humoral immunity contributory but not the only injury mechanism.

Serologic activity and morphologic injury must be interpreted together.

HUMORAL COMPONENT

Autoantibody synthesis

Immune complexes

Local inflammatory response

Potential synovial injury

Slide 26 · Multiple mechanisms converge at the synovium

CD4⁺ T-cell cytokines recruit and stimulate inflammatory cells.

Macrophage mediators drive protease release and cellular activation.

Osteoclasts erode bone; Proliferating synovium erodes cartilage.

The integrated lesion is a chronically inflamed, destructive pannus.

PATHOGENESIS INTEGRATED

Inflammatory synovium

Proteases → cartilage

RANKL → osteoclasts

Pannus, erosions, instability

Slide 27 · Normal joint anatomy defines the target tissues

Articular cartilage covers the opposing bone surfaces.

Synovial lining borders the noncartilaginous inner joint surface.

Subchondral bone supports the articular cartilage.

RA preferentially creates proliferative inflammatory synovium at these interfaces.

ANATOMIC REFERENCE

Joint section — schematic

Subchondral bone

Intact cartilage + thin synovium

Slide 28 · Early synovitis begins with edema and thickening

The synovial membrane becomes edematous and expanded.

Synovial cells proliferate, creating an abnormally thick lining.

Chronic inflammation accumulates beneath the lining.

These early changes precede advanced structural destruction.

EARLY MORPHOLOGY

Joint section — schematic

Subchondral bone

Synovial expansion

Slide 29 · Synovial lining hyperplasia is a hallmark

The normally thin synovial cell population undergoes proliferation.

Thickened lining increases the volume of actively inflamed synovium.

The surface no longer retains its usual smooth appearance.

Hyperplasia contributes to pannus rather than forming a benign neoplastic mass.

HISTOLOGIC FEATURE 1

Synovial cell proliferation

Thickened lining surface

Inflammatory stromal expansion

Foundation for pannus

Slide 30 · Villous change reflects synovial proliferation

The expanded synovium forms delicate or bulbous villous projections.

The villi contain inflamed and often vascular stromal tissue.

This describes gross/microscopic synovial architecture, not osteophyte formation.

The resulting membrane can extend over articular surfaces.

SYNOVIAL ARCHITECTURE

Synovial edema

Lining hyperplasia

Bulbous / delicate villi

Expanding inflamed membrane

Slide 31 · Inflammatory infiltrates are mixed and chronic

CD4⁺ T cells, B cells, plasma cells, dendritic cells, and macrophages are prominent.

Cellular infiltrates often become dense in the synovium.

B cells may organize into follicle-like aggregates.

The infiltrate is a substrate for locally amplified immune responses.

HISTOLOGIC FEATURE 2

CD4⁺ helper T cells

B cells and plasma cells

Dendritic cells

Macrophages

Slide 32 · Lymphoid follicle formation indicates organization

Synovial B cells can form secondary lymphoid follicle-like structures.

Germinal-center–type organization is described in RA synovium.

Plasma cells are often abundant in surrounding inflammatory tissue.

Such organization helps explain local autoantibody production.

FOLLICULAR IMMUNITY

B-cell accumulation

Lymphoid follicle formation

Plasma cell differentiation

Local antibody production

Slide 33 · Synovial plasma cells sustain humoral activity

Plasma cells within RA synovium secrete immunoglobulins.

A proportion of these immunoglobulins recognize self-antigens.

Autoantibody production also occurs in lymphoid organs outside joints.

Local antibodies coexist with cellular cytokine-driven tissue destruction.

HUMORAL MICROENVIRONMENT

Autoantibody production

Synovial plasma cells

Systemic lymphoid tissues

Circulating + local antibodies

Slide 34 · Angiogenesis sustains the inflammatory pannus

The synovium develops increased vascularity through angiogenesis.

New vessels accompany chronically inflamed proliferating tissue.

The vascular network facilitates continued arrival of leukocytes.

Angiogenesis is one of the characteristic histologic changes in RA.

HISTOLOGIC FEATURE 3

Chronic synovitis

Angiogenic response

Expanded vascular supply

Sustained cell recruitment

Slide 35 · Fibrin-rich surface exudate is characteristic

Fibrin-rich exudates may cover the synovial and joint surfaces.

Neutrophils can be present within the exudate.

This feature is compatible with inflammatory synovitis despite the term “nonsuppurative.”

It must not be confused with the purulent fluid of bacterial septic arthritis.

HISTOLOGIC FEATURE 4

Surface fibrin

Neutrophils in exudate

Chronically inflamed synovium

Not equivalent to septic pus

Slide 36 · Osteoclasts create marginal bone erosions

Osteoclastic activity increases in adjacent subchondral bone.

Inflamed synovium can extend into areas of bone resorption.

Periarticular erosions and subchondral cysts may result.

The bone loss contrasts with osteophytic remodeling in OA.

HISTOLOGIC FEATURE 5

Synovial inflammation

RANKL / osteoclast response

Bone resorption

Marginal erosion + cyst

Slide 37 · Pannus is destructive inflammatory tissue

Pannus contains edematous synovium, inflammatory cells, fibroblasts, and granulation tissue.

It grows across articular cartilage rather than remaining confined to the lining.

Proteolysis and cellular invasion progressively damage cartilage.

Pannus is the defining structural bridge from synovitis to articular destruction.

PANNUS CONCEPT

Joint section — schematic

Subchondral bone

Pannus encroaches on cartilage

Slide 38 · Pannus extension explains progressive cartilage loss

Proliferating synovium advances over the joint surface.

Inflammatory proteases degrade the cartilage matrix.

Joint-space narrowing follows as cartilage is lost.

Cartilage erosion and bone resorption contribute to deformity and loss of function.

LOCAL DAMAGE PROGRESSION

Villous proliferative synovium

Pannus over cartilage

Proteolytic matrix damage

Joint-space narrowing

Slide 39 · Cartilage injury and bone erosion are coupled

Matrix degradation predominantly injures cartilage.

Osteoclast-mediated resorption erodes subchondral or marginal bone.

Both changes follow immune activation but involve different cellular effectors.

Combined damage progressively destabilizes the joint.

TWO DESTRUCTIVE EFFECTORS

Immune inflammation

Synovial proteases → cartilage

Osteoclasts → bone

Loss of joint integrity

Slide 40 · Ankylosis develops after severe destruction

After cartilage destruction, pannus may connect opposing bony surfaces.

Fibrous tissue can bridge the joint, producing fibrous ankylosis.

Later ossification can produce bony ankylosis and joint fusion.

Fusion is a possible advanced consequence—not inevitable for every RA patient.

LATE JOINT OUTCOME

Cartilage destruction

Pannus bridges joint

Fibrous ankylosis

Bony ankylosis

Slide 41 · Joint remodeling represents a temporal sequence

Early RA: Edematous, inflamed, hyperplastic synovium.

Intermediate RA: Destructive pannus with cartilage and bone erosion.

Advanced RA: Reduced joint space, deformity, or ankylosis.

The rate and ultimate extent of structural injury vary among patients.

STAGE CONCEPT

Early: Synovitis + villi

Intermediate: Pannus + erosion

Advanced: Deformity ± ankylosis

Slide 42 · Five defining morphologic features of RA synovitis

Finding

Tissue process

Pathologic significance

Synovial hyperplasia

Lining-cell proliferation

Expanded intimal membrane

Inflammatory infiltrate

T / B cells, macrophages

Sustained autoimmunity

Angiogenesis

Increased synovial vessels

Chronic inflammatory support

Fibrin-rich exudate

Surface fibrin ± neutrophils

Inflamed joint surface

Osteoclast activity

Bone resorption

Periarticular erosions

Slide 43 · Rheumatoid nodules are an extraarticular lesion

Nodules are described as an infrequent RA manifestation.

They typically present as small, firm, nontender subcutaneous masses.

Classic sites include forearms, elbows, occiput, and lumbosacral region.

Their characteristic pathology differs from destructive synovial pannus.

EXTRAARTICULAR MORPHOLOGY

Forearm / elbow

Occiput

Lumbosacral region

Firm, nontender nodules

Slide 44 · Rheumatoid nodules contain central fibrinoid necrosis

The nodule has a central zone of fibrinoid necrosis.

Activated macrophages form a surrounding palisading rim.

Lymphocytes and plasma cells occupy the outer inflammatory zone.

This organized lesion is a morphologic correlate of systemic RA.

NODULE HISTOARCHITECTURE

Rheumatoid nodule — schematic

Fibrinoid necrosis

Palisaded macrophages

Slide 45 · RA-associated vasculitis indicates severe disease

Severe RA can be associated with leukocytoclastic vasculitis.

The source describes an acute necrotizing vascular inflammatory pattern.

Vascular lesions may involve vessels associated with pleura, pericardium, or lung.

Some organ inflammation can evolve into chronic fibrosis.

SYSTEMIC VASCULAR INJURY

Severe RA

Necrotizing vasculitis

Pleura / pericardium / lung

Possible fibrosing change

Slide 46 · Lung and cardiac involvement extend RA beyond joints

Extraarticular disease may involve the lungs and heart.

Inflammation in pleural or pericardial regions can occur in severe systemic disease.

Chronic inflammatory injury can produce fibrosing consequences.

Organ findings require clinicopathologic interpretation rather than assuming joint-limited illness.

SYSTEMIC DISTRIBUTION

Pulmonary involvement

Pleural inflammation

Pericardial inflammation

Possible chronic fibrosis

Slide 47 · Ocular inflammation is a recognized complication

Uveitis among possible RA-associated ocular findings.

Keratoconjunctivitis may also develop.

Dry-eye–type changes can resemble manifestations of Sjögren syndrome.

Ocular disease is part of the differential assessment of systemic manifestations.

OCULAR INVOLVEMENT

Uveitis

Keratoconjunctivitis

Overlap with sicca patterns

Slide 48 · Some patients have a systemic prodrome

About half of patients are described as developing malaise, fatigue, and generalized pain initially.

Joint involvement may follow over weeks to months.

This prodrome can precede an easily recognized inflammatory polyarthritis.

Clinical chronology therefore contributes to suspicion of RA.

EARLY PRESENTATION

Malaise and fatigue

General musculoskeletal pain

Weeks to months

Inflammatory joint disease

Slide 49 · RA usually begins in small peripheral joints

Symptoms commonly first affect the hands and feet.

Wrist and ankle involvement may follow.

Elbow and knee involvement is also described.

The common distribution is symmetric, although the pattern can vary.

ANATOMICAL DISTRIBUTION

Hands and feet first

Wrists and ankles next

Elbows and knees later

Often symmetric

Slide 50 · MCP and PIP joint disease is characteristic

In the hand, RA commonly affects metacarpophalangeal (MCP) joints.

Proximal interphalangeal (PIP) joints are another typical site.

This pattern helps distinguish RA from the characteristic OA distribution.

Foot small-joint involvement adds diagnostic context.

HAND JOINT PATTERN

Typical hand involvement

MCP

Involved

PIP

Involved

Small foot joints

Involved

DIP

Not emphasized

Slide 51 · Inflammatory pain is worse after rest

Involved RA joints are painful, warm, and swollen.

Pain commonly worsens in the morning or after inactivity.

This timing contrasts with pain associated chiefly with joint use in OA.

Symptoms reflect active synovial inflammation rather than only structural wear.

SYMPTOM QUALITIES

RA pain pattern

OA pain pattern

Morning or post-rest pain

Warm, swollen joints

Use-related mechanical pain

Less primary synovitis

Slide 52 · Chronic disease impairs joint movement

Many patients experience a waxing-and-waning inflammatory course.

Over time, the joints may enlarge and lose range of motion.

Progressive cartilage loss, erosions, and deformity impair function.

A minority—often seronegative—may stabilize or regress.

FUNCTIONAL OUTCOME

Recurrent inflammation

Structural damage

Enlarged / deformed joints

Reduced range of motion

Slide 53 · ACPA is useful but does not replace examination

ACPA detection supports RA among inflammatory polyarthritides.

The serum test is not positive in every patient.

Its meaning must be integrated with joint pattern and evidence of inflammation.

A negative result cannot independently exclude RA.

SEROLOGIC REASONING

Clinical inflammatory arthritis

ACPA testing

Interpret result in context

Integrate with imaging

Slide 54 · Rheumatoid factor requires cautious interpretation

RF supports diagnosis but is not unique to RA.

A substantial majority of patients may be RF positive.

Some individuals without RA have measurable RF.

Absence of RF does not remove the possibility of RA.

TEST LIMITATIONS

RF positive ≠ proof of RA

RF negative ≠ exclusion

Interpret with ACPA + clinic

Slide 55 · Seronegative RA remains a clinical diagnosis

Approximately 20% of RA patients are seronegative.

Negative ACPA and RF do not automatically negate clinically compatible RA.

Joint distribution and characteristic radiographic changes remain important.

Synovial tissue biopsy is rarely required.

DIAGNOSTIC PITFALL

Inflammatory joint findings

ACPA / RF may be negative

Clinical + radiographic correlation

RA still possible

Slide 56 · Imaging reveals accumulated structural injury

Typical described changes include juxtaarticular osteopenia.

Periarticular bone erosions provide evidence of destructive arthritis.

Loss of articular cartilage is associated with joint-space narrowing.

These changes are complementary to clinical and serologic evaluation.

RADIOGRAPHIC MORPHOLOGY

Juxtaarticular osteopenia

Periarticular erosions

Joint-space narrowing

Cartilage loss

Slide 57 · Diagnosis is a synthesis, not a single marker

Examine for persistent inflammatory and often symmetric peripheral arthritis.

Assess typical small-joint distribution, swelling, warmth, and post-rest symptoms.

Use ACPA and RF as supportive laboratory evidence.

Evaluate imaging for erosions, osteopenia, and joint-space loss.

DIAGNOSTIC WORKFLOW

Clinical pattern

Serology

Radiographic morphology

Integrated RA assessment

Slide 58 · Rheumatoid arthritis versus osteoarthritis: Mechanism

Slide 59 · Rheumatoid arthritis versus osteoarthritis: Presentation

Slide 60 · Therapy targets inflammation and structural injury

Clinical aims include pain relief and reduction of inflammatory activity.

Disease-modifying treatment seeks to slow or arrest joint destruction.

The source describes glucocorticoids and methotrexate among treatments.

Biologic therapies target mediators or lymphocyte responses.

PATHOLOGY–TREATMENT LINK

Suppress inflammation

Reduce synovial activation

Limit cartilage / bone injury

Preserve joint function

Slide 61 · TNF inhibition validates a major disease mechanism

Therapeutic TNF antagonism provides strong support for TNF-mediated injury.

Biologic inhibition may control inflammation but does not cure RA.

Disease flares can follow discontinuation of effective TNF blockade.

Prolonged anti-TNF therapy increases susceptibility to opportunistic infection, including tuberculosis.

BENEFIT–RISK CONTEXT

TNF blockade

Lower inflammatory signaling

Reduced disease activity

Infection risk: E.g. Tuberculosis

Slide 62 · Targeting T and B cells reflects immune complexity

T cells orchestrate cytokine-mediated inflammation.

B cells and plasma cells provide an autoantibody component.

Additional biologic agents that interfere with T- and B-cell responses.

This mechanistic diversity helps explain why RA cannot be reduced to one cytokine.

MULTIPLE THERAPEUTIC TARGETS

Immune-directed therapy

T-cell responses

B-cell responses

Control of autoimmune synovitis

Slide 63 · Case interpretation: Symmetric small-joint arthritis

An adult has swelling, warmth, and pain in symmetric MCP and PIP joints. Symptoms are most troublesome after waking or prolonged inactivity.

Clinicopathologic questions

Which aspects favor inflammatory RA over OA?

What tests and radiographic features would provide additional support?

Slide 64 · Case interpretation: Pathology-to-clinic

Persistent synovitis accounts for warmth, swelling, and post-rest discomfort.

Hyperplasia, angiogenesis, and immune infiltrates expand synovial tissue.

Protease-rich pannus produces cartilage loss and joint-space narrowing.

Osteoclastic activity produces characteristic periarticular erosions.

CASE SOLUTION

Synovitis

Joint warmth + swelling

Pannus + osteoclasts

Cartilage loss + erosion

Slide 65 · Case interpretation: Seronegative erosive disease

A patient has persistent symmetric small-joint inflammatory arthritis and erosive radiographic change, but both ACPA and RF are reported negative.

Clinicopathologic questions

Can rheumatoid arthritis still be considered?

Why is joint biopsy usually not the next routine step?

Slide 66 · Case interpretation: Negative serology is not exclusion

Antibodies are probabilistic adjuncts, not defining tissue lesions.

A compatible symmetric inflammatory phenotype can persist despite negative markers.

Radiographic erosions provide structural corroboration.

A negative serologic result should prompt integration of all evidence rather than diagnostic closure.

CASE SOLUTION

Clinical phenotype

Radiographic structural injury

Serology interpreted contextually

Slide 67 · Synthesis: Immune cells explain morphologic lesions

Th1 / Th17: IFN-γ and IL-17 support local inflammatory activation and recruitment.

Macrophages: TNF, IL-1, and IL-6 stimulate destructive synovial responses.

T-cell RANKL: Osteoclastic bone erosion.

B cells / plasma cells: ACPA, RF, and possible immune-complex contributions.

IMMUNE → MORPHOLOGY

Autoreactive T / B cells

Cytokines + antibodies

Proliferative synovitis

Pannus / cartilage / bone injury

Slide 68 · Synthesis: Recognize the signature phenotype

Chronic, often symmetric small-joint inflammatory arthritis.

Hyperplastic villous synovium with chronic immune infiltration and angiogenesis.

Destructive pannus with cartilage and bone erosions.

ACPA/RF often supportive; Systemic manifestations and nodules may occur.

FOUR DIAGNOSTIC ANCHORS

Symmetric MCP / PIP pattern

Inflammatory synovitis

Pannus + erosions

± Antibodies / extraarticular disease

Slide 69 · Principal reference and image-use statement

Robbins, Cotran & Kumar

Pathologic Basis of Disease · 11th edition (2026)

Chapter 26, “Bones, Joints, and Soft Tissue Tumors”

Rheumatoid Arthritis, printed pp. 1089–1091

Textbook Table 26.5 supplies the RA–OA comparison.

Figures are original editable schematic representations; no histologic specimen has been simulated.