Juvenile Idiopathic Arthritis

Slide 1 · Juvenile idiopathic arthritis

A clinicopathologic framework for childhood inflammatory arthritis

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Define JIA and explain why it is a heterogeneous disease group.

Distinguish major clinical phenotypes and immune mechanisms.

Relate synovial inflammation to joint damage, extra-articular disease and growth.

Apply diagnostic, uveitis-screening and treatment principles to cases.

Slide 3 · JIA is a clinical umbrella diagnosis

Arthritis begins before age 16 and persists for at least 6 weeks

A group of disorders of unknown cause—not one molecularly uniform condition.

Requires evaluation for infectious, malignant, mechanical and other inflammatory causes.

The 6-week threshold is a disease-definition requirement, not permission to delay assessment.

Slide 4 · The diagnosis has three core components

Childhood onset

First arthritis occurs before 16 years

Persistence

Inflammatory arthritis lasts ≥6 weeks

Exclusion

No better established explanation

Slide 5 · Why a single JIA label is insufficient

Joint distribution

Oligoarticular or polyarticular disease

Systemic inflammation

Fever, rash and visceral involvement in systemic disease

Immune phenotype

RF, ANA and enthesitis patterns vary

Complications

Uveitis, growth effects or macrophage activation syndrome

Slide 6 · JIA differs from adult rheumatoid arthritis

Juvenile idiopathic arthritis

Oligoarthritis and large-joint disease are prominent.

Systemic manifestations are relatively more common.

ANA positivity is familiar in subsets; Nodules are usually absent.

Adult rheumatoid arthritis

Often symmetric small-joint polyarthritis.

ACPA/RF and adult RA synovitis inform comparison.

Rheumatoid nodules can be a feature of established adult RA.

Slide 7 · Textbook epidemiologic context

30,000–50,000 affected individuals in the United States

Estimate quoted by Robbins 11th edition; Not an annual incidence figure.

JIA subtype frequencies depend on case definitions and population.

Do not generalize an overall figure to one JIA subtype.

Slide 8 · Historical names do not describe one entity

Earlier terminology

Juvenile rheumatoid arthritis (JRA)

Juvenile chronic arthritis (JCA)

Different grouping rules hindered comparisons.

Contemporary umbrella term

Juvenile idiopathic arthritis (JIA)

Defined by age, duration and exclusions.

Subclassification is phenotype-based.

Slide 9 · ILAR classification recognizes seven groups

Clinical category

Defining organizing feature

Oligoarthritis

1–4 joints in first 6 months

Polyarthritis, RF-negative

≥5 joints; RF negative

Polyarthritis, RF-positive

≥5 joints; Repeat RF positivity

Systemic arthritis

Arthritis plus characteristic systemic syndrome

Psoriatic arthritis

Arthritis with psoriasis-related features

Enthesitis-related arthritis

Arthritis and/or enthesitis pattern

Undifferentiated arthritis

Does not fit one category exclusively

Slide 10 · Classification uses multiple axes

Joint count

1–4 or ≥5 during first 6 months

Clinical phenotype

Systemic, psoriatic or enthesitis features

Serology and exclusions

RF status; Other required ILAR conditions

Slide 11 · Oligoarthritis: Limited joint count

One to four joints during the first 6 months

Typically affects large joints, especially knee or ankle.

A lower joint count does not eliminate the risk of vision-threatening uveitis.

Clinical joint examination, not antibody positivity alone, defines arthritis.

Slide 12 · Persistent versus extended oligoarthritis

Persistent

No more than four joints involved throughout the course.

May remain localized but warrants long-term monitoring.

Ophthalmic screening remains risk-based.

Extended

More than four joints become involved after month six.

Change is defined by subsequent joint accumulation.

Can require treatment escalation for additional active joints.

Slide 13 · RF-negative polyarthritis

At least five inflamed joints during the first six months.

Rheumatoid factor is negative under the ILAR category definition.

Joint distribution and disease activity may vary considerably.

Negative RF does not exclude chronic erosive inflammatory arthritis.

Slide 14 · RF-positive polyarthritis

Five or more affected joints in the initial six months.

ILAR requires at least two RF-positive tests, three or more months apart.

Resembles adult seropositive rheumatoid arthritis more than many other JIA groups.

RF is a classification feature here, not a universal JIA screening diagnosis.

Slide 15 · Systemic JIA is biologically distinct

Fever

Characteristic repeated spikes of systemic inflammation

Rash

Transient erythematous eruption often accompanies fever

Visceral findings

Lymphadenopathy, hepatosplenomegaly or serositis

Arthritis

May develop alongside or after systemic symptoms

Slide 16 · Psoriatic-pattern JIA

Psoriasis-associated arthritis is a separate ILAR category.

Nail pitting, onycholysis and dactylitis help establish the phenotype.

Psoriasis may be absent when other specified features are present.

Be careful not to classify arthritis from a nonspecific rash alone.

Slide 17 · Enthesitis-related arthritis

Peripheral phenotype

Arthritis and/or inflammation at tendon insertion

Axial association

Inflammatory back pain or sacroiliac disease may emerge

Supportive context

HLA-B27, acute anterior uveitis, family history

Slide 18 · Undifferentiated JIA: A real classification result

Some patients meet no single ILAR category.

Others fulfill features of two or more categories.

A classification category is not a measure of severity.

Phenotype reassessment remains important as disease evolves.

Slide 19 · ILAR and provisional PRINTO frameworks

ILAR (Edmonton revision)

Seven named categories.

Joint count and exclusion rules central.

Widely used in published JIA studies.

Provisional PRINTO revisions

Focus on more biologically coherent groups.

Emphasize early-onset ANA-positive and Still/enthesitis phenotypes.

Provisional research classification—not a universal replacement.

Slide 20 · Different patterns imply different surveillance

Phenotype

Priority complication / feature

Early ANA-positive oligoarthritis

Chronic anterior uveitis

Systemic JIA / Still disease

Macrophage activation syndrome

RF-positive polyarthritis

Persistently active joint disease

Enthesitis-related arthritis

Axial disease; Acute anterior uveitis

TMJ involvement in any category

Growth, function and jaw symmetry

Slide 21 · JIA pathogenesis remains incompletely defined

Genetic susceptibility + dysregulated inflammation ≠ a single proven cause

Genetic associations and Th1/Th17-related inflammation.

Mechanisms and importance vary markedly between JIA phenotypes.

Avoid assuming that all JIA is identical to adult RA.

Slide 22 · Genetic susceptibility is contributory

HLA variants

Immune recognition and antigen presentation associations

PTPN22 variants

Association with immune signaling susceptibility

Inflammatory response

Expression depends on phenotype and other factors

Slide 23 · T-helper-cell pathways in inflammatory JIA

Adaptive immune activation

T-cell responses in susceptible hosts

Th1 and Th17 involvement

Immune-cell recruitment and cytokine signaling

Synovial inflammation

Persistent tissue-level inflammatory response

Slide 24 · Inflammatory mediators named

IL-1

Innate inflammatory signaling; Therapeutically important in systemic JIA

IL-17

Associated with Th17-type immune responses

TNF

Inflammatory signaling; Established therapeutic target in some phenotypes

IFN-γ

Th1-associated mediator; Relevant to inflammatory pathways

Slide 25 · Why IL-6 matters to JIA

Successful treatment with an IL-6 receptor antibody.

Systemic JIA features a major cytokine-driven inflammatory component.

IL-6 receptor inhibition is a phenotype-specific therapeutic strategy.

A drug response supports pathway relevance but does not prove a unique cause.

Slide 26 · Systemic JIA: Innate-immune emphasis

Systemic inflammation

Fever, rash and acute-phase response

IL-1 / IL-6 activity

Central clinically actionable pathways

Inflammatory sequelae

Arthritis and possible MAS complication

Slide 27 · Synovial architecture: Conceptual map

Simplified architecture, not an observed clinical specimen

Joint cavity / inflammatory effusion

Thickened, inflamed synovium

Articular cartilage

Subchondral bone

Pathologic link

Synovial immune activation

Inflammatory proliferation

Potential joint injury

Slide 28 · Synovitis produces clinically observable swelling

Vascular activation

Synovial hyperemia and fluid accumulation

Synovial proliferation

Lining thickening and inflammatory infiltration

Functional effect

Warmth, effusion, pain and loss of motion

Slide 29 · What chronic inflammation can do to a joint

Persistent synovitis

Inflammatory tissue persists

Cartilage/bone injury

Potential erosion and joint-space damage

Long-term consequence

Stiffness, contracture or altered function

Slide 30 · Adult RA pannus: Useful context, not a JIA criterion

Shared inflammatory concept

Hyperplastic synovium can become destructive.

Synovitis can precede cartilage and bone damage.

Inflammation is an actionable target.

Important limitation

Pannus directly for adult RA.

The JIA excerpt does not establish identical histology.

Biopsy is not a routine way to assign ILAR subtype.

Slide 31 · Growing joints create pediatric complications

Growth plate context

Inflammation may disturb local growth patterns

Joint contracture

Persistent loss of range restricts function

Limb asymmetry

Asymmetric disease may affect limb growth

TMJ growth

Mandibular growth and facial symmetry warrant attention

Slide 32 · Morphology must answer a clinical question

Histology may show chronic synovitis, but it is not diagnostic by itself.

Inflammation is evaluated primarily by clinical examination and selected imaging.

Tissue sampling is reserved for atypical presentations or suspected mimics.

Do not interpret a schematic as histologic proof of JIA.

Slide 33 · Clinical arthritis is more than arthralgia

Inflammatory arthritis

Objective joint swelling or effusion.

Restricted range or painful motion.

Morning stiffness or stiffness after inactivity.

Isolated pain

Pain without objective inflammation is nonspecific.

Consider mechanical, infectious and malignant causes.

Reassess if symptoms or examination evolve.

Slide 34 · Large-joint involvement is a major clue

Knee and ankle involvement are characteristic of many oligoarticular presentations.

Joint distribution should be documented anatomically and longitudinally.

Asymmetry and a low joint count do not imply a benign course.

Different distributions direct different differential diagnoses.

Slide 35 · Extra-articular manifestations are phenotype-specific

Eye

Chronic or acute anterior uveitis depending on phenotype

Skin

Psoriatic features or systemic evanescent rash

Systemic organs

Fever, serositis and reticuloendothelial enlargement

Growth/function

Limb and mandibular developmental effects

Slide 36 · JIA-associated chronic anterior uveitis

Sight-threatening inflammation can be clinically silent

Absence of redness, pain or photophobia does not exclude chronic anterior uveitis.

Screen with slit-lamp examination at a risk-based interval.

Ocular complications may develop before symptoms become obvious.

Slide 37 · Who needs frequent uveitis screening?

JIA phenotype

Oligo / RF-negative poly / psoriatic / undifferentiated

Additional risk features

ANA positive; Onset younger than 7 years; Disease ≤4 years

High-risk schedule

Eye examination every 3 months (ACR 2019, conditional)

Slide 38 · Do not conflate two uveitis patterns

Chronic anterior uveitis

Often asymptomatic at onset.

Associated with younger, ANA-positive phenotypes.

Planned slit-lamp screening is essential.

Acute anterior uveitis

May cause pain, redness and photophobia.

Can occur with HLA-B27 / enthesitis-related phenotype.

Acute symptoms require urgent assessment.

Slide 39 · Macrophage activation syndrome is an emergency

A hyperinflammatory complication of systemic JIA / Still disease

Consider when systemic disease deteriorates with persistent fever.

May progress to coagulopathy, organ dysfunction and critical illness.

Requires urgent specialist evaluation—do not wait for full diagnostic criteria.

Slide 40 · MAS recognition: Discordant laboratory trends

Ferritin

Markedly elevated or rapidly increasing

Cell counts

Falling platelets / cytopenias despite inflammation

Coagulation

Falling fibrinogen and coagulopathy

Other markers

Rising transaminases and triglycerides

Slide 41 · TMJ arthritis may be clinically subtle

Temporomandibular inflammation can occur without obvious pain.

Chronic disease may impair mandibular growth and oral function.

Clinical assessment may be supplemented by targeted imaging.

Management deserves attention even when other joints are quiet.

Slide 42 · Why disability can outlast active inflammation

Active arthritis

Pain, effusion and restricted movement

Secondary consequences

Muscle weakness, contracture, altered growth

Persistent limitation

Functional difficulty despite reduced inflammation

Slide 43 · JIA is a diagnosis of exclusion

Confirm inflammatory joint findings

History, examination and symptom chronology

Look for danger signals

Infection, malignancy, trauma, multisystem illness

Investigate selectively

Laboratory and imaging tests answer focused questions

Classify after evaluation

Apply clinical phenotype and defined criteria

Slide 44 · Acute hot monoarthritis: Exclude infection first

Septic arthritis is a time-critical mimic

Fever, severe focal pain, inability to bear weight or marked illness increase concern.

Obtain urgent evaluation and appropriate joint-fluid studies when indicated.

A child does not become “JIA” merely because joint swelling persists.

Slide 45 · Malignancy and hematologic disease can mimic JIA

Leukemia and other marrow disorders may present with limb pain or joint symptoms.

Night pain, constitutional symptoms, unusual bruising or abnormal blood counts are warnings.

Inconsistent objective joint findings should prompt reconsideration.

Do not initiate immunosuppressive treatment before important mimics are addressed.

Slide 46 · Differential diagnosis is pattern dependent

Presentation

Alternatives to consider

Acute monoarthritis

Septic arthritis, trauma, osteomyelitis

Symmetric small-joint polyarthritis

Viral/postinfectious arthritis; Connective tissue disease

Persistent fever with joint pain

Infection, malignancy, autoinflammatory disease

Enthesitis / axial symptoms

Juvenile spondyloarthritis and infection

Intermittent isolated pain

Mechanical and non-inflammatory causes

Slide 47 · What ANA and RF actually contribute

Antinuclear antibody (ANA)

Common in important JIA subsets.

Aids uveitis risk stratification.

Not diagnostic in isolation.

Rheumatoid factor (RF)

Repeated positivity helps classify RF-positive polyarthritis.

Negative result does not exclude JIA.

Not a universal disease activity measure.

Slide 48 · Inflammatory laboratory results need context

ESR and CRP may support active inflammation but do not confirm JIA.

CBC can reveal inflammation—or signals pointing to infection, malignancy or MAS.

Normal inflammatory markers do not exclude all JIA phenotypes.

Use laboratory results with examination and trajectory, not as a stand-alone verdict.

Slide 49 · Choosing imaging for the clinical question

Modality

Best teaching role

Ultrasound

Detect synovitis/effusion; Guide selected injections

MRI

Evaluate deep synovitis, marrow and complex joints

Radiographs

Identify structural damage or alternative diagnosis

Targeted TMJ imaging

Evaluate a potentially occult high-impact joint

Slide 50 · A normal radiograph does not exclude synovitis

Plain films are insensitive for early inflammation

ACR 2021 recommends against obligatory radiography before advanced imaging to find active synovitis or enthesitis.

Use radiographs for structural damage or differential diagnosis when appropriate.

Unnecessary imaging requirements can delay care.

Slide 51 · A practical diagnostic pathway

Inflammatory arthritis suspected

Joint examination and chronology

Red flags?

Urgent assessment for infection / malignancy / MAS

Exclusion and targeted testing

CBC, inflammatory markers, serology, imaging as indicated

Longitudinal phenotype

Joint count, systemic signs and extra-articular surveillance

Slide 52 · Clinical risk changes initial treatment planning

High-risk joint

Hip, wrist, ankle, sacroiliac or TMJ

Structural damage

Erosion or progressive limitation

Burden of disease

Many active joints, high inflammatory activity

Delayed diagnosis

Long untreated inflammatory course

Slide 53 · Treatment targets inflammation and function

Suppress active inflammation

Minimize pain and prevent ongoing injury

Preserve joint structure

Avoid erosive and growth-related damage

Protect participation

Mobility, school activity, vision and well-being

Slide 54 · Oligoarthritis: Staged pharmacologic care

Initial measures

Scheduled NSAID trial and/or intra-articular glucocorticoid

Persistent active disease

Conventional DMARD—methotrexate preferred

Inadequate response

Biologic DMARD when warranted

Slide 55 · Polyarticular disease needs early control

Persistent multiple-joint inflammation risks progressive structural and functional consequences.

Conventional DMARDs such as methotrexate are widely used.

Biologic agents target inflammatory mediators or lymphocyte signaling.

Therapy is phenotype- and response-dependent, not determined by joint count alone.

Slide 56 · Systemic JIA: Targeted cytokine blockade

Recognize systemic phenotype

Fever, rash, systemic inflammation with or without arthritis

Choose targeted therapy

IL-1 or IL-6 blockade is central in current guidance

Evaluate for complications

Ongoing surveillance for MAS and lung involvement

Slide 57 · Systemic corticosteroid exposure matters

Glucocorticoids can rapidly reduce severe systemic inflammation.

Chronic exposure creates important pediatric toxicity and growth concerns.

Current Still-disease guidance prioritizes early IL-1/IL-6 blockade to limit prolonged systemic steroids.

Individualize treatment during severe illness or macrophage activation syndrome.

Slide 58 · Uveitis treatment follows ocular activity

Initial ocular control

Topical glucocorticoid for active anterior uveitis

Steroid dependence / persistence

Systemic methotrexate when indicated

Refractory/high-risk course

Monoclonal anti-TNF therapy in selected patients

Slide 59 · Medication safety and immunizations

Monitoring

CBC, liver function and renal tests according to drug

Infection risk

Screen for tuberculosis before biologic DMARDs

Vaccines

Keep inactivated immunizations current

Coordination

Plan live vaccines around immunosuppression

Slide 60 · Rehabilitation is not optional

Physical therapy helps maintain range of motion, strength and mobility.

Occupational therapy supports daily activities and school participation.

Monitor pain, fatigue, growth, function and quality of life.

Individualize activity while controlling active synovitis.

Slide 61 · Longitudinal follow-up has several targets

Domain

What changes clinical decisions?

Articular

Active/swollen joints, range of motion and function

Ocular

Slit-lamp screening findings and uveitis treatment

Systemic

Fever pattern, rash, serositis, MAS laboratory signals

Medication

Efficacy, toxicity and infection prevention

Development

Growth, jaw/limb symmetry, school participation

Slide 62 · Prognosis is heterogeneous

Serious functional disability occurs in ~10%

The figure is the 11th-edition textbook estimate, not an individual risk prediction.

Chronic disease persists in many patients; Others achieve sustained inactivity.

Phenotype, joint damage, extra-articular disease and treatment response matter.

Slide 63 · Case 1: Painless swollen knee

Illustrative vignette — not patient data

A 5-year-old has a persistently swollen knee and morning limping for 9 weeks.

No major systemic illness; Inflammatory arthritis is confirmed on examination.

ANA is positive; RF is negative.

Question: Which classification pattern and associated screening need are suggested?

Slide 64 · Case 1: Interpretation

Most likely working phenotype

Oligoarticular JIA if mimics are excluded.

Joint count in the first six months determines initial class.

The positive ANA is supportive, not diagnostic.

Critical next action

Arrange ophthalmic slit-lamp screening.

Younger ANA-positive onset is high-risk for chronic anterior uveitis.

Use a risk-based follow-up interval.

Slide 65 · Case 2: Fever, arthritis and falling platelets

Illustrative vignette — not patient data

A child with systemic JIA develops persistent fever and worsening illness.

Ferritin rises rapidly; Platelets and fibrinogen fall.

Transaminases and triglycerides increase.

Question: What complication must be addressed urgently?

Slide 66 · Case 2: Interpretation

Suspect macrophage activation syndrome immediately

Converging clinical deterioration and abnormal laboratory trends are high-risk.

Seek urgent specialist and inpatient assessment; Do not await a solitary confirmatory test.

Treat the underlying hyperinflammation using an expert-directed approach.

Slide 67 · Three recurring diagnostic mistakes

Premature labeling

Not excluding septic arthritis or malignancy

Antibody overreach

Treating ANA or RF as a definitive JIA diagnostic test

Ocular omission

Assuming asymptomatic children cannot have uveitis

Phenotype conflation

Applying one immune model or treatment to every subgroup

Slide 68 · Integrating phenotype, pathology and consequence

Disease feature

Mechanistic / practical implication

Oligoarticular, ANA-associated

Immune-mediated synovitis; Eye screening

RF-positive polyarticular

RA-like inflammatory phenotype; Joint protection

Systemic JIA

Cytokine-driven inflammation; MAS vigilance

Enthesitis-related

Insertions / axial pattern; Uveitis phenotype

TMJ arthritis

Potential growth and functional damage

Slide 69 · Five concepts to retain

JIA begins before 16 years and persists for at least 6 weeks after exclusion of alternatives.

Subtypes are clinically heterogeneous; ANA/RF are contextual markers.

Th1/Th17 and cytokines contribute, but no universal causal pathway is established.

Quiet uveitis and fulminant MAS demand different surveillance strategies.

Early individualized inflammation control aims to protect joints, growth and function.

Slide 70 · Core readings and clinical frameworks

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

Petty RE et al. ILAR classification, Edmonton revision. J Rheumatol. 2004;31:390–392.

Angeles-Han ST et al. ACR uveitis guideline. Arthritis Care Res. 2019;71:703–716.

Onel KB et al. ACR JIA therapeutic guideline. Arthritis Rheumatol. 2022;74:553–569.

Onel KB et al. ACR monitoring/imaging guideline. Arthritis Rheumatol. 2022;74:570–585.

Fautrel B et al. EULAR/PReS Still-disease recommendations. Ann Rheum Dis. 2024;83:1614–1627.