Rheumatoid Arthritis

Slide 1 · Rheumatoid Arthritis

Autoimmune mechanisms · synovial morphology · clinicopathologic correlation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · The central clinicopathologic problem

RA is a chronic autoimmune disorder in which proliferative synovitis drives joint damage.

An inflamed synovial membrane expands into a destructive pannus.

Cartilage loss, periarticular bone erosion and sometimes ankylosis follow.

Extraarticular involvement confirms that RA is a systemic immune disease.

Slide 3 · Learning outcomes

Connect loss of self-tolerance to T-cell, B-cell and macrophage responses.

Explain how cytokines, proteases and osteoclasts produce specific joint lesions.

Recognize the defining synovial and rheumatoid-nodule morphology.

Interpret joint distribution, serology, radiography and principal differentials.

Slide 4 · RA and primary osteoarthritis: Distinct initiating processes

Rheumatoid arthritis

Primary autoimmune synovitis

Inflammatory pannus is destructive

Systemic manifestations may occur

Osteoarthritis

Primary cartilage injury and degeneration

Inflammation may exacerbate damage

Usually confined to joints

Slide 5 · Why the synovium matters

Joint cavity

Articular cartilage

Subchondral bone

Synovium

Schematic — not a specimen

Intact joint

Uninflamed synovial lining

A normal joint has a smooth articular surface and a thin synovial lining.

Slide 6 · Nonsuppurative proliferative synovitis

“Synovitis” identifies synovial membrane inflammation as the principal lesion.

“Proliferative” denotes synoviocyte expansion and thickened synovial projections.

“Nonsuppurative” distinguishes chronic immune synovitis from purulent bacterial arthritis.

The lesion ultimately extends beyond synovium into cartilage and adjacent bone.

Slide 7 · Population pattern

US prevalence is approximately 0.25%–1% in the supplied edition.

Incidence peaks during the third and fourth decades of life.

Females are affected approximately three times as often as males.

These are textbook estimates, not current population surveillance statistics.

Slide 8 · Why RA is classified as an autoimmune disease

T lymphocytes react to self-antigens associated with joint tissues.

Many patients produce autoantibodies to modified self-proteins and IgG.

Susceptibility alleles and environmental candidates are implicated.

Immune-directed treatment reduces inflammation and joint injury.

Slide 9 · The disease spans joints and extraarticular tissues

Autoimmune response

Loss of self-tolerance

Synovial inflammation

Persistent inflammatory cells and cytokines

Tissue injury

Cartilage erosion and bone loss

Systemic lesions

Skin, lung, heart and vessels

The joint lesion is the dominant expression of systemic autoimmunity.

Schematic

Slide 10 · The initiating joint antigen is not established

CD4+ helper T-cell reactivity is central to the pathogenic model.

Candidate targets include collagen and chemically modified peptides.

Multiple joint antigens have been proposed; No single initiating antigen is proven.

This uncertainty matters when distinguishing a plausible mechanism from a demonstrated cause.

Slide 11 · Predisposition to chronic autoimmune arthritis

Inherited risk

Susceptibility genes, including HLA associations

Environmental candidates

Smoking and possibly infection/periodontitis

Altered self-proteins

Posttranslational citrullination may generate epitopes

Immune activation

Responses to joint-associated self-antigens

The proposed sequence is multifactorial; Triggers remain incompletely defined.

Schematic

Slide 12 · Genetic contribution: Risk, not destiny

That inherited susceptibility accounts for about half of RA risk.

This estimate describes population-level genetic contribution, not individual prediction.

Genetic predisposition influences development, persistence and progression.

Environmental exposures and immune regulation remain necessary considerations.

Slide 13 · HLA-DR4 and ACPA-positive disease

The HLA-DR4 allele is associated with the ACPA-positive subset of RA.

Class II HLA molecules present peptide antigens to CD4+ T cells.

Proposed molecular mimicry involving some microbial epitopes.

An HLA association supports susceptibility but is not a stand-alone diagnostic test.

Slide 14 · Environmental factors: Proposed triggers

Smoking may promote modification of self-proteins through citrullination.

Infection, including periodontitis, is discussed as a possible contributor.

The source explicitly states that environmental determinants are not clearly defined.

Do not assume that a proposed association identifies a proven causal exposure.

Slide 15 · Citrullination can alter immune recognition

Self-protein

Peptide contains arginine residue

Modification

Arginine is converted to citrulline

Modified epitope

New or altered antibody/T-cell target

Autoimmunity

Response may persist in susceptible hosts

Citrullination is established; Its precise initiating role in any given case is uncertain.

Schematic

Slide 16 · Joint proteins implicated as ACPA targets

Citrullinated fibrinogen and type II collagen are among described targets.

Modified α-enolase and vimentin are additional candidate antigens.

A broad antigen repertoire is consistent with multiple self-reactivities.

A target antigen is not automatically the initiating cause of the disease.

Slide 17 · CD4+ T-cell activation initiates amplification

Self-antigen presentation

HLA class II-dependent antigen recognition

CD4+ helper response

Inflammatory Th1 and Th17 pathways

Myeloid-cell activation

Macrophages and synovial cells release mediators

Local tissue damage

Leukocytes, proteases and osteoclasts

T-cell–driven inflammation links failed tolerance to destructive synovitis.

Schematic

Slide 18 · Th1 cells: The macrophage-activation arm

Th1 helper cells release interferon-γ (IFN-γ).

IFN-γ activates macrophages and resident synovial cells.

Activated cells participate in chronic inflammation and tissue injury.

The Th1 effect is complementary to other helper-T-cell pathways.

Slide 19 · Th17 cells recruit additional inflammatory cells

Th17 cells release interleukin-17 (IL-17).

IL-17 recruits neutrophils and monocytes into inflammatory sites.

Incoming cells help sustain the inflamed synovial environment.

Cell recruitment converts antigen-specific activation into widespread joint inflammation.

Slide 20 · Macrophages amplify destructive inflammation

Immune activation

T-cell cytokines stimulate macrophages

TNF, IL-1, IL-6

Inflammatory mediators released

Synovial activation

Recruitment and protease induction

Cartilage injury

Degradation exceeds local preservation

Macrophage-derived cytokines link immune activation to matrix destruction.

Schematic

Slide 21 · TNF is a major inflammatory mediator

TNF contributes to leukocyte recruitment and persistent synovial inflammation.

It helps induce proteolytic pathways that damage articular cartilage.

The therapeutic benefit of TNF antagonists supports its pathogenic importance.

TNF is an important mediator, not the sole explanation for RA.

Slide 22 · IL-1 and IL-6 reinforce synovitis

Macrophage-derived IL-1 and IL-6 act alongside TNF.

These cytokines support inflammatory-cell recruitment.

They stimulate synovial cells toward cartilage-degrading protease production.

Parallel cytokine activities help sustain the destructive inflammatory milieu.

Slide 23 · Cartilage destruction is cytokine-linked

TNF / IL-1 / IL-6

Inflammatory signaling in synovium

Synovial cells

Production of matrix-degrading proteases

Hyaline cartilage

Extracellular matrix is degraded

Joint surface

Irreversible structural loss may develop

An immune lesion causes mechanical failure by degrading cartilage.

Schematic

Slide 24 · RANKL provides a mechanism for bone erosion

Activated T cells

Express RANKL

Osteoclast stimulation

Increased bone-resorptive activity

Marginal / subchondral bone

Periarticular erosions and cysts

Joint architecture

Progressive structural damage

Cartilage and bone destruction involve distinct cellular effectors.

Schematic

Slide 25 · B-cell responses are part of RA synovitis

The inflamed synovium often contains B cells and abundant plasma cells.

Lymphoid follicles with germinal centers may appear locally.

Some plasma cells secrete antibodies recognizing self-antigens.

Autoantibodies can also be produced in lymphoid organs outside the joint.

Slide 26 · Where autoantibodies fit in the lesion

B-cell activation

Lymphoid organs and synovial follicles

Plasma cells

Production of autoantibodies

Immune complexes

May accumulate within joints

Inflammatory amplification

Potential antibody-associated contribution

Antibody-mediated mechanisms are plausible contributors, not the only known cause.

Schematic

Slide 27 · ACPA: Anti–citrullinated peptide antibodies

ACPAs recognize epitopes created by citrullination of proteins.

The supplied Robbins text describes detection in up to 70% of RA patients.

They are diagnostically useful and associated with an important immune phenotype.

The source suggests—but does not establish completely—a contribution to severity and persistence.

Slide 28 · Rheumatoid factor targets immunoglobulin G

Rheumatoid factors bind the Fc region of IgG.

The source describes IgM and IgA rheumatoid-factor autoantibodies.

Rheumatoid factors are found in approximately 80% of persons with RA.

They may occur in people without RA and are absent in some affected patients.

Slide 29 · ACPA and rheumatoid factor answer different questions

Feature

ACPA

Rheumatoid factor

Antigen

Citrullinated self-peptides

Fc region of IgG

Main value

Supports RA diagnosis

Supports RA diagnosis

In supplied source

Up to 70% of patients

About 80% of patients

Limitation

Not universal

May also occur without RA

Slide 30 · Immune complexes: Contributory rather than exhaustive

Rheumatoid factor can participate in immune-complex formation.

Immune complexes may be deposited within joints.

T-cell cytokines, macrophages and osteoclasts remain central in the mechanism.

RA cannot be reduced to a purely immune-complex arthritis.

Slide 31 · The destructive RA network

Autoimmune T/B-cell responses

Inflammation and autoantibody production

Macrophages / synovium

Cytokines, leukocyte recruitment and proteases

Osteoclasts / cartilage

Bone resorption and matrix degradation

Several linked effector pathways converge on joint destruction.

Schematic

Slide 32 · Separate demonstrated events from hypotheses

Established in the source: Synovial inflammation, autoantibodies, pannus and erosions.

Well-supported mediators: TNF, IL-1, IL-6, IL-17, IFN-γ and RANKL.

Less certain: The initial antigen and exact environmental trigger.

The balance of T-cell and antibody contributions is not identical in every patient.

Slide 33 · Synovial transformation in early RA

Joint cavity

Articular cartilage

Subchondral bone

Villous hyperplasia

Schematic — not a specimen

Early RA

Thickened, villous synovium

Synovial hypertrophy, inflammation and angiogenesis precede tissue destruction.

Slide 34 · Synovium changes from smooth to villous

Inflamed synovium becomes thickened, edematous and hyperplastic.

Its previously smooth contour develops delicate and bulbous villi.

Villi expand the surface of inflammatory synovial tissue.

Villous hyperplasia is one characteristic feature of chronic RA synovitis.

Slide 35 · Microscopic signature: Synoviocyte proliferation

Synovial lining cells proliferate in response to sustained inflammation.

The expanded lining is part of the synovial hypertrophy seen grossly.

The pathologic lining sits adjacent to inflammatory exudate and cartilage.

It participates in the formation of a growing pannus.

Slide 36 · Microscopic signature: Inflammatory cell mixture

CD4+ T lymphocytes are prominent in the synovial inflammatory infiltrate.

B lymphocytes, plasma cells, dendritic cells and macrophages are also present.

The infiltrate explains ongoing local cytokine and antibody production.

The composition supports immune-mediated rather than purely degenerative disease.

Slide 37 · Lymphoid follicles and local immune organization

B-cell aggregates can form recognizable follicles within inflamed synovium.

Secondary follicles may contain germinal centers.

Plasma-cell accumulation accompanies chronic antigen-driven responses.

These findings help explain local autoantibody production.

Slide 38 · Synovial angiogenesis sustains inflammation

Vascularity increases because new vessels form within diseased synovium.

Angiogenesis supports an expanded mass of inflammatory tissue.

Blood vessels provide routes for continued leukocyte recruitment.

The result is a metabolically active, enlarging synovial lesion.

Slide 39 · Fibrin and neutrophils at the articular surface

A fibrin-rich exudate coats synovial and articular surfaces.

Neutrophils are found within the exudate.

This surface exudate coexists with a predominantly chronic cellular infiltrate.

Neutrophils here do not make RA equivalent to septic suppurative arthritis.

Slide 40 · Osteoclastic activity marks the bone interface

Osteoclast activity increases in bone neighboring inflamed synovium.

Activated synovial tissue can invade periarticular bone.

This produces marginal erosions and subchondral cysts.

Bone erosion is a structural consequence of inflammatory osteoclast stimulation.

Slide 41 · Five pathologic components of RA synovitis

Component

Morphologic change

Clinicopathologic significance

Lining cells

Hyperplasia and villi

Expanding synovial mass

Leukocytes

T, B, plasma, myeloid cells

Immune activity

Microvessels

Angiogenesis

Inflammatory supply

Articular surface

Fibrin-rich neutrophilic exudate

Active surface inflammation

Bone interface

Osteoclasts and erosions

Structural joint injury

Slide 42 · Pannus: Inflammatory tissue becomes invasive

Joint cavity

Articular cartilage

Subchondral bone

Pannus

Schematic — not a specimen

Progressive RA

Pannus invading articular tissues

Inflammatory pannus expands over cartilage and promotes erosion at joint margins.

Slide 43 · What constitutes a pannus?

Edematous hyperplastic synovium forms its scaffold.

Inflammatory cells, fibroblasts and granulation tissue expand the lesion.

The pannus extends over articular cartilage.

It promotes erosion of cartilage and ultimately altered joint architecture.

Slide 44 · Pannus converts inflammation to joint destruction

Hyperplastic synovium

Villi and inflammatory stromal tissue

Pannus formation

Advancing tissue over articular cartilage

Cartilage erosion

Loss of the smooth load-bearing surface

Ankylosis in some cases

Fibrous bridging and possible ossification

Pannus is not simply a synonym for synovial swelling.

Schematic

Slide 45 · Cartilage erosion and bone erosion are distinct

Synovial proteases degrade articular cartilage matrix.

Activated osteoclasts resorb periarticular and subchondral bone.

The pathways intersect but are not anatomically identical.

Both contribute to reduced joint space, deformity and limited movement.

Slide 46 · How inflammatory fusion can develop

Persistent synovitis

Proliferative inflammatory pannus

Cartilage loss

Apposing articular structures become damaged

Fibrous ankylosis

Pannus bridges opposing bones

Bony ankylosis

Fibrous bridge may ossify

Ankylosis is a late potential outcome, not a necessary feature of every case.

Schematic

Slide 47 · Fibrous and bony ankylosis are sequential possibilities

Fibrous ankylosis

Fibrous tissue bridges a joint

Mechanical movement becomes restricted

May precede ossification

Bony ankylosis

Ossified bridge fuses opposing bones

Represents structural bone fusion

Late destructive joint consequence

Slide 48 · Rheumatoid nodules: Extraarticular morphology

They are described as an infrequent manifestation of RA.

Typical sites include subcutaneous forearm and elbow regions.

Occipital and lumbosacral sites are also described.

The nodules are usually small, firm, oval and nontender.

Slide 49 · Rheumatoid nodule: A layered necrobiotic lesion

Fibrinoid necrosis

Palisaded activated macrophages

Lymphocytes and plasma cells around the rim

Schematic — not a histologic specimen

Slide 50 · Systemic vasculitis in severe RA

Severe disease may be accompanied by leukocytoclastic vasculitis.

An acute necrotizing process affecting small and large arteries.

Pleural, pericardial and pulmonary tissues may be involved.

Some vascular and serosal lesions later evolve toward fibrosis.

Slide 51 · Extraarticular pulmonary and cardiac disease

RA-associated pathology may extend into lungs and pleura.

Cardiac and pericardial involvement are also recognized.

Vascular lesions can overlap with other systemic autoimmune phenotypes.

A joint-predominant presentation does not exclude important visceral injury.

Slide 52 · Ocular manifestations fit systemic autoimmunity

Uveitis can occur in the setting of RA.

Keratoconjunctivitis and sicca-like changes may accompany disease.

The textbook explicitly cross-references Sjögren syndrome.

Extraarticular symptoms merit evaluation beyond the joint examination.

Slide 53 · Systemic symptoms can precede arthritis

The source describes malaise, fatigue and generalized musculoskeletal pain.

In about half of patients, these symptoms precede joint involvement.

Recognizable arthritis may appear over subsequent weeks or months.

The prodrome reflects the systemic nature of the inflammatory process.

Slide 54 · RA typically presents as symmetric polyarthritis

Small joints of the hands and feet are characteristically involved early.

Joint involvement is usually approximately symmetric.

Larger joints may be affected as disease progresses.

The pattern is a strong clinical clue, not a substitute for full evaluation.

Slide 55 · Joint distribution: Hands and feet first

Hand and foot symptoms are generally prominent early.

Wrists and ankles are subsequently common sites.

Elbows and knees may be involved with wider disease.

Small-joint predominance helps differentiate RA from primary OA.

Slide 56 · Hand-joint distribution guides differential diagnosis

Typical RA distribution

Metacarpophalangeal joints

Proximal interphalangeal joints

Symmetric small-joint inflammation

Primary osteoarthritis emphasis

Degenerative articular cartilage pathology

Different hand-joint pattern

Often weight-bearing joints elsewhere

Slide 57 · Inflammatory pain follows inactivity

RA joints are characteristically swollen, warm and painful.

Pain commonly worsens in the morning or after inactivity.

Inflammatory stiffness differs from the typical mechanical OA pattern.

Link this timing to active synovitis rather than cartilage wear alone.

Slide 58 · Clinical swelling reflects synovial disease

Synovial hypertrophy increases the volume of periarticular tissue.

Inflammatory exudation contributes to effusions.

Warmth and tenderness track active inflammatory changes.

Progressive structural damage restricts range of motion.

Slide 59 · Natural history is heterogeneous

Most cases follow a chronic course with episodes of increased and decreased activity.

Continued activity can cause joint enlargement and declining motion.

Some patients, particularly seronegative ones, stabilize or regress.

Robbins also describes a small group with abrupt, severe polyarticular onset.

Slide 60 · Periarticular inflammation produces deformity

Tendons, ligaments and adjacent soft tissues can also become inflamed.

Progressive soft-tissue changes affect joint alignment and function.

Ulnar deviation and flexion–hyperextension deformities may develop.

The characteristic appearance reflects both synovial destruction and periarticular injury.

Slide 61 · Interpreting hand deformities carefully

Ulnar deviation describes deviation of fingers toward the ulnar side.

Flexion–hyperextension deformity describes abnormal postures across finger joints.

These are distinct descriptors, not interchangeable synonyms.

Clinical configuration must be described explicitly rather than inferred from a label.

Slide 62 · Radiographic signs of structural RA

Joint effusions may accompany active synovial inflammation.

Juxtaarticular osteopenia is a characteristic associated finding.

Periarticular erosions reflect osteoclast-mediated bone destruction.

Joint-space narrowing reflects cartilage loss.

Slide 63 · Clinical diagnosis integrates three evidence types

Clinical pattern

Symmetric inflammatory small-joint arthritis

Serology

ACPA and rheumatoid factor

Imaging

Osteopenia, erosions and space narrowing

No single test replaces the overall clinicopathologic assessment.

Schematic

Slide 64 · ACPA is useful but not universal

A positive ACPA test helps support RA in an appropriate clinical setting.

The source states that detection is possible in up to 70% of patients.

A negative ACPA assay cannot, by itself, exclude RA.

Interpret serology together with joint pattern and radiographic changes.

Slide 65 · Rheumatoid factor requires contextual interpretation

Rheumatoid factor is common in RA but not specific to it.

Some people without RA may have detectable rheumatoid factor.

Some patients with definite RA have no rheumatoid factor.

The diagnostic question is whether laboratory results fit the inflammatory joint phenotype.

Slide 66 · Seronegative RA is a recognized diagnosis

That about 20% of patients are seronegative.

In seronegative patients, diagnosis relies on clinical and radiographic features.

Negative autoantibody tests do not erase synovitis and erosive morphology.

Tissue biopsy is rarely required in the routine diagnostic approach.

Slide 67 · Why routine synovial biopsy is seldom necessary

A characteristic clinical distribution often directs the diagnostic workup.

Serology and radiographic evidence are supportive.

Chronic synovial inflammation itself is not unique to RA.

Biopsy is therefore rarely needed for typical cases, according to the source.

Slide 68 · Rheumatoid arthritis versus osteoarthritis

Feature

Rheumatoid arthritis

Osteoarthritis

Pathogenic driver

Autoimmune synovitis

Mechanical cartilage injury

Inflammation

Primary, persistent

May be secondary

Joint predilection

Small joints, polyarticular

Weight-bearing joints

Morphology

Pannus, erosions; possible fusion

Cartilage damage, osteophytes, cysts

Serology / organs

ACPA, RF; extraarticular lesions

No characteristic autoantibodies or systemic disease

Slide 69 · RA versus spondyloarthritis: Tissue compartment

Rheumatoid arthritis

Synovial inflammation is dominant

Symmetric small-joint disease is typical

ACPA or RF may be present

Spondyloarthropathies

Inflammation frequently targets entheses

Sacroiliac and vertebral involvement

HLA-B27 association; Often RF absent

Slide 70 · RA versus septic arthritis: Urgency and mechanism

Rheumatoid arthritis

Chronic autoimmune synovitis

Often symmetric polyarticular pattern

Nonsuppurative inflammatory lesion

Acute bacterial arthritis

Direct microbial infection of a joint

Typically abrupt painful single joint

Aspiration and organism identification are important

Slide 71 · Therapy is directed at immunologic injury

Treatment seeks to reduce pain and inflammation.

An equally important goal is to slow or arrest irreversible joint destruction.

Corticosteroids and methotrexate among treatment options.

Mechanism-directed biologic approaches target TNF or lymphocyte responses.

Slide 72 · Why blocking TNF can improve RA

TNF signaling

Leukocyte recruitment and inflammatory amplification

TNF antagonism

Interrupts one major inflammatory pathway

Reduced synovitis

Less cytokine-driven tissue injury

Long-term management

Disease control is not the same as cure

Therapeutic success is evidence of TNF involvement, not exclusive causation.

Schematic

Slide 73 · Anti-TNF therapy introduces infection risk

TNF antagonists suppress an important arm of host inflammatory defense.

The source specifically highlights increased risk of opportunistic infection.

Mycobacterium tuberculosis is a named example.

This is a therapeutic risk-benefit implication, not a reason to mislabel RA as infection.

Slide 74 · Application case: Inflammatory small-joint disease

Hypothetical patient: Symmetric pain and swelling in metacarpophalangeal and proximal interphalangeal joints, with prominent stiffness on waking. ACPA is detected.

Which immune and morphologic mechanisms best explain this pattern?

Slide 75 · Case interpretation: Link phenotype and tissue injury

Symmetric small-joint inflammation favors an RA-type clinicopathologic pattern.

ACPA supports autoimmunity involving citrullinated antigens.

CD4+ responses, macrophage cytokines and hyperplastic synovium explain active synovitis.

Pannus, proteases and osteoclasts explain later cartilage and bone destruction.

Slide 76 · Application case: Antibodies are absent

Hypothetical patient: Chronic symmetric inflammatory arthritis of the hands and wrists; ACPA and rheumatoid factor are both negative. Radiographs show periarticular erosions and joint-space narrowing.

Does negative serology exclude rheumatoid arthritis?

Slide 77 · Case interpretation: Seronegative does not mean noninflammatory

The absence of ACPA and rheumatoid factor does not rule out RA.

A compatible clinical pattern and structural radiographic findings retain diagnostic value.

Other causes of inflammatory arthritis still require differential assessment.

The source states that biopsy is seldom necessary for a typical clinical picture.

Slide 78 · Mechanistic synthesis: One disease, linked compartments

Failed immune tolerance

Self-reactive T/B-cell responses

Synovial inflammation

Cytokines, angiogenesis and villous proliferation

Destructive pannus

Cartilage matrix damage and osteoclast erosion

Clinical disease

Pain, deformity, stiffness and systemic lesions

RA is an autoimmune synovitis whose tissue damage produces its clinical phenotype.

Schematic

Slide 79 · Eight findings to retain

RA is a systemic autoimmune disease centered on chronic proliferative synovitis.

CD4+ T cells, cytokine-activated macrophages and B cells participate.

TNF, IL-1, IL-6, IL-17, IFN-γ and RANKL connect inflammation to tissue damage.

Pannus destroys cartilage; Osteoclasts cause erosions; Ankylosis may develop.

ACPA and RF assist diagnosis; Neither is universally positive.

Slide 80 · Primary Robbins references

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. 2026.

“Rheumatoid Arthritis” within the Diseases of the Immune System section.

“Rheumatoid Arthritis” within the Bones, Joints, and Soft Tissue Tumors section.

“Comparative Features of Osteoarthritis and Rheumatoid Arthritis.”