Reactive Arthritis

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Lecture topics

Opening case: A painful swollen knee
Clostridioides difficile is also listed
Population frequency
Achilles tendon insertion: A characteristic site
Ocular involvement also includes uveitis
Recurrence occurs in nearly half of patients
Case I: Connect three clinical domains
Final clinicopathologic synthesis

Slide index & full transcript (62 slides)

Text from the original slides, in presentation order. Diagrams and images remain in the viewer above.

Slide 1 · Reactive Arthritis

Postinfectious arthritis · enthesitis · systemic manifestations

Pathology lecture

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Recognize the infection-associated timing and characteristic peripheral joint distribution.

Explain enthesitis, dactylitis, and axial involvement as linked musculoskeletal patterns.

Identify genitourinary, ocular, mucocutaneous, and cardiac manifestations.

Distinguish a postinfectious presentation from directly infected joints using Robbins-based contrasts.

Clinical pattern recognition—not a validated diagnostic criteria set.

Slide 3 · Opening case: A painful swollen knee

A young adult develops abrupt swelling of one knee after an episode of gastrointestinal illness. Heel pain appears during the following weeks.

Which historical and examination features matter most?

Clinical reasoning

Does the infection–joint sequence suggest a postinfectious syndrome?

Discuss the temporal relationship, distribution, and extra-articular clues.

Slide 4 · The classical clinical triad

Arthritis is the defining musculoskeletal component.

Nongonococcal urethritis or cervicitis is the genitourinary component.

Conjunctivitis is the ocular component.

The classical formulation links the triad to a preceding infection.

Arthritis

Urethritis / cervicitis

Conjunctivitis

Slide 5 · Reactive arthritis now has a broader definition

The full classical triad is not required in the expanded textbook definition.

Monoarthritis or oligoarthritis may appear days to weeks after a relevant infection.

Genitourinary and gastrointestinal infections are recognized triggering contexts.

Genitourinary or enteric infection

Days to weeks

Acute mono-/oligoarthritis

Slide 6 · Temporal sequence is central

The inciting infection occurs before onset of arthritis.

Joint symptoms develop over a days-to-weeks interval.

A focused history should connect a preceding infection with the new joint pattern.

Temporal association is useful but cannot establish the mechanism by itself.

Genitourinary or enteric infection

Days to weeks

Acute mono-/oligoarthritis

Slide 7 · Classical triad versus clinical spectrum

Dimension

Classical description

Expanded spectrum

Joint disease

Arthritis

Mono- or oligoarthritis

Genitourinary

Urethritis / cervicitis

Can precede or accompany arthritis

Ocular disease

Conjunctivitis

Conjunctivitis or uveitis may occur

Trigger

Following infection

GU or gastrointestinal infection

The additional manifestations expand recognition beyond the three-part historical description.

Slide 8 · Genitourinary trigger: Chlamydia

Chlamydia is the explicitly named genitourinary pathogen.

Arthritis may arise after the genitourinary episode rather than concurrently.

Urethritis or cervicitis supplies a relevant clinical history.

A history of an infection-associated sequence links organ systems.

Genitourinary or enteric infection

Days to weeks

Acute mono-/oligoarthritis

Slide 9 · Gastrointestinal triggers: Shigella and Salmonella

Shigella and Salmonella are among the named enteric antecedents.

The acute intestinal event may have preceded musculoskeletal symptoms by days or weeks.

A recent gastrointestinal illness can guide clinical pattern recognition.

Genitourinary

Gastrointestinal

Chlamydia

Shigella

Salmonella

Yersinia

Campylobacter

C. Difficile

Slide 10 · Gastrointestinal triggers: Yersinia and Campylobacter

Yersinia and Campylobacter are additional recognized triggering organisms.

Robbins separately notes Campylobacter-associated reactive arthritis in HLA-B27 carriers.

The trigger list illustrates heterogeneous bacterial antecedents, not a unique organism.

Genitourinary

Gastrointestinal

Chlamydia

Shigella

Salmonella

Yersinia

Campylobacter

C. Difficile

Slide 11 · Clostridioides difficile is also listed

Clostridioides difficile is included among the textbook’s gastrointestinal antecedents.

The infection-associated joint syndrome is not restricted to the three classic enteric genera.

The broad trigger list should not be mistaken for evidence of identical pathogen mechanisms.

Genitourinary

Gastrointestinal

Chlamydia

Shigella

Salmonella

Yersinia

Campylobacter

C. Difficile

Slide 12 · HIV-positive patients can be affected

Reactive arthritis may develop in people living with HIV.

The associated arthritis in this setting to pathogens other than HIV.

Avoid claiming that HIV itself is the demonstrated arthritogenic trigger in this passage.

HIV status is clinical context, not proof of an HIV-specific cause.

Slide 13 · Organize the recognized antecedents

Genitourinary: Chlamydia.

Gastrointestinal: Shigella, Salmonella, Yersinia, Campylobacter, C. Difficile.

These etiologic groups converge on an infection-associated inflammatory joint phenotype.

Genitourinary

Gastrointestinal

Chlamydia

Shigella

Salmonella

Yersinia

Campylobacter

C. Difficile

Slide 14 · HLA-B27 is a common association

HLA-B27 is frequently present in patients with reactive arthritis.

It is also a shared feature within the seronegative spondyloarthropathy group.

The source does not provide an HLA-B27 sensitivity or diagnostic cutoff for reactive arthritis.

HLA-B27

Common association

Association ≠ stand-alone diagnosis

Slide 15 · Reactive arthritis in the spondyloarthropathy family

Seronegative spondyloarthropathies typically lack rheumatoid factor.

Entheses are important sites of pathology in the group.

Axial involvement and HLA-B27 association are recurring group characteristics.

Bony proliferation can lead to ankylosis within this disease family.

Spondyloarthropathy spectrum

Enthesitis

Axial involvement

HLA-B27 association

New bone formation

Slide 16 · Genetic association is not diagnostic proof

HLA-B27 as common—not universal—in reactive arthritis.

The same association occurs in related spondyloarthropathies.

Do not substitute a single susceptibility marker for the infection–joint–extra-articular pattern.

HLA-B27

Common association

Association ≠ stand-alone diagnosis

Slide 17 · An immune-mediated explanation is proposed

Robbins suggests T-cell responses in the spondyloarthropathy group.

Potential microbial antigens may cross-react with musculoskeletal antigens.

The putative antigens are not definitively identified in the supplied passage.

Preceding bacterial infection

Host immune response

Musculoskeletal inflammation

Detailed pathogenic antigens and cells remain uncertain

Slide 18 · Pathogenic uncertainty must remain visible

Infection precedes arthritis, but a precise causal immune pathway is not established here.

HLA-B27 association does not identify the specific pathogenic antigen.

The source does not assign a confirmed cell type, cytokine hierarchy, or organism-specific molecular pathway to reactive arthritis.

Preceding bacterial infection

Host immune response

Musculoskeletal inflammation

Detailed pathogenic antigens and cells remain uncertain

Slide 19 · Typical age at presentation

Young adults are the most commonly affected age group.

Age is supportive epidemiologic context—not a substitute for the clinical phenotype.

The source does not state that the syndrome is confined to young adults.

Common in young adults; Consider the presentation rather than an age cutoff.

Slide 20 · Population frequency

A global prevalence of approximately 30 per 100,000 adults.

This is an approximate population estimate, not an individual predicted risk.

Do not extrapolate this number to different settings or times without additional evidence.

≈30

Per 100,000 adults

Approximate global prevalence stated

Slide 21 · A characteristic acute peripheral presentation

The initial arthritis typically begins acutely.

The joint pattern is usually asymmetric.

A limited number of joints are affected (oligoarthritis).

Lower-extremity joints are especially characteristic.

Knee: Frequent arthritis

Heel: Frequent enthesitis

Digits: Possible dactylitis

Slide 22 · Asymmetry is a useful pattern clue

Affected joints need not mirror one another across the body.

An asymmetric distribution helps define the usual early phenotype.

The term describes distribution, not the severity of the inflammatory process.

Knee: Frequent arthritis

Heel: Frequent enthesitis

Digits: Possible dactylitis

Slide 23 · Monoarthritis and oligoarthritis are both included

One inflamed joint is compatible with the expanded definition.

A few inflamed joints are also compatible.

The pattern must be interpreted alongside a recent relevant infectious episode.

A single acutely swollen joint still requires consideration of other causes.

Monoarthritis

Oligoarthritis

One joint

A few joints

Included in definition

Context remains vital

Slide 24 · The lower limb is preferentially involved

Initial inflammation frequently targets lower-extremity joints.

The knee is singled out as an especially common site.

The distribution differs from the small-joint emphasis typical of rheumatoid arthritis.

Knee: Frequent arthritis

Heel: Frequent enthesitis

Digits: Possible dactylitis

Slide 25 · Knee arthritis and heel enthesitis are different lesions

Knee arthritis signifies inflammation within a joint.

Heel enthesitis signifies inflammation at tendon/ligament insertions into bone.

Both may coexist in the same spondyloarthropathy phenotype.

Knee arthritis

Heel enthesitis

Synovial joint

Insertional site

Swollen knee

Swollen heel

Peripheral arthritis

Entheseal inflammation

Slide 26 · Inflammatory low-back pain extends the phenotype

Inflammatory low-back pain commonly accompanies the peripheral arthritis.

This symptom signals possible involvement of the axial musculoskeletal system.

Pain in the back can coexist with knee-predominant lower-extremity disease.

Peripheral synovitis

Inflammatory low-back pain

Possible axial spondyloarthritis

Slide 27 · An enthesis is a tendon/ligament attachment

Enthesitis means inflammation where a tendon or ligament attaches to bone.

Such lesions are prominent within the spondyloarthropathy family.

At the heel, the key calcaneal insertions include Achilles tendon and plantar fascia.

Tendon / fascia

Attachment site

Calcaneus

Simplified editable enthesis schematic; Not a specimen.

Slide 28 · Achilles tendon insertion: A characteristic site

The Achilles tendon inserts onto the calcaneus.

Inflammation at this enthesis contributes to heel swelling.

A complaint centered at the tendon insertion is distinct from primary ankle-joint synovitis.

Tendon / fascia

Attachment site

Calcaneus

Simplified editable illustration of insertional inflammation.

Slide 29 · Plantar fascia insertion: Another heel target

The plantar fascia insertion on the calcaneus.

Inflammation at this site is part of the enthesitis pattern.

Concurrent Achilles and plantar insertional symptoms localize pathology to the heel entheses.

Tendon / fascia

Attachment site

Calcaneus

Slide 30 · Why the heel becomes swollen

The immediate lesion is inflammation at a tendon/ligament insertion.

The calcaneus is the bony attachment common to the named heel sites.

This anatomy explains the characteristic heel-centered swelling.

Tendon / fascia

Attachment site

Calcaneus

Slide 31 · Dactylitis produces a “sausage” digit

Dactylitis is inflammation affecting a digit.

It is present in a minority of patients with reactive arthritis.

Diffuse swelling produces the characteristic sausage-like appearance.

Swollen digit

Tendon sheath

Synovitis

Schematic

Original schematic of a swollen digit; Not a clinical photograph.

Slide 32 · Tendon-sheath synovitis explains dactylitis

Robbins specifically attributes digit swelling to synovitis of a digital tendon sheath.

The inflammation is not limited to one interphalangeal joint.

This mechanism accounts for the diffuse digit contour.

Swollen digit

Tendon sheath

Synovitis

Schematic

Slide 33 · Inflammation can be followed by ossification

Tendoligamentous insertion sites can undergo ossification.

Calcaneal spurs and other bony outgrowths may result.

This is a structural consequence of insertional disease—not a universal early finding.

Preceding bacterial infection

Host immune response

Eye: Conjunctivitis and uveitis.

Urogenital tract: Urethritis, cervicitis, balanitis.

Mucocutaneous tissue: Mucosal ulcers and psoriasis-like nail changes.

Cardiac valves: Aortic insufficiency is an uncommon potential concern, frequency unspecified.

Eyes

Conjunctivitis · uveitis

Urogenital

Urethritis · cervicitis · balanitis

Mucosa / skin

Ulcers · nail changes

Heart

Aortic insufficiency (possible)

Slide 43 · Arthritis may wax and wane for months

A typical episode is not necessarily a single continuously worsening event.

Fluctuations over a period of months.

The longitudinal course may include remissions and renewed symptoms.

Acute onset

Waxing / waning over months

Recurrence in many patients

Slide 44 · Recurrence occurs in nearly half of patients

Recurrent arthritis in nearly 50% of patients.

Recurrent tendinitis and lumbosacral pain are part of the same long-term burden.

This estimate does not imply identical duration or severity for every patient.

≈50%

Have recurrent symptoms

Robbins: Nearly half experience recurrence

Slide 45 · Recurrent symptoms need not be purely articular

Arthritis can recur.

Tendinitis can recur even when the most prominent complaint is not joint swelling.

Lumbosacral pain may persist or recur as an axial feature.

Acute onset

Waxing / waning over months

Recurrence in many patients

Slide 46 · Spinal involvement can resemble ankylosing spondylitis

Some patients develop a spondyloarthritis phenotype.

Axial involvement may be indistinguishable from ankylosing spondylitis.

This highlights clinical overlap within the HLA-B27-associated disease family.

Peripheral synovitis

Inflammatory low-back pain

Possible axial spondyloarthritis

Slide 47 · Reactive arthritis versus ankylosing spondylitis

Feature

Reactive arthritis

Ankylosing spondylitis

Defining context

After GU / GI infection

Axial-predominant inflammatory disease

Peripheral joints

Asymmetric lower-limb oligoarthritis

Hips, knees, shoulders may be involved

Axial involvement

Possible; May be indistinguishable

Sacroiliac and vertebral joints prominent

HLA-B27

Common

≈90% positive

Comparison derives from adjacent Robbins subsections; Not a formal diagnostic algorithm.

Slide 48 · Reactive arthritis versus direct infectious arthritis

Feature

Reactive arthritis

Infectious arthritis

Clinical relationship

Arthritis after a distant infection

Microorganisms seed the joint

Common pattern

Asymmetric mono-/oligoarthritis

Often acutely painful monoarthritis

Mechanism in source

Postinfectious inflammatory syndrome

Hematogenous, direct, or contiguous spread

Diagnostic priority

Synthesize triggering illness and phenotype

Identify organisms in joint fluid when suspected

Infection inside the joint remains a separate consideration; The comparison is not a rule-out test.

Slide 49 · A rapidly destructive infected joint is a critical mimic

Microorganisms can reach joints through blood, inoculation, or contiguous spread.

Cartilage has limited regenerative capacity, so bacterial destruction may become permanent.

A suspected suppurative joint infection requires prompt identification and effective antimicrobial treatment.

Acute swollen joint

Direct joint infection must be considered

Rapid destruction in suppurative arthritis.

Slide 50 · Rheumatoid arthritis has a different usual pattern

RA commonly has a chronic, symmetric inflammatory polyarthritis pattern.

Reactive arthritis typically begins as acute asymmetric lower-limb oligoarthritis.

Both can cause joint swelling; Distribution and clinical context improve discrimination.

The comparison does not exclude atypical presentations.

Reactive

Rheumatoid

Postinfectious context

Autoimmune synovitis

Asymmetric / few joints

Usually symmetric / multiple

Entheseal clues

Progressive synovial destruction

Slide 51 · Clinical synthesis: Clues should converge

Recent gastrointestinal or genitourinary illness: Temporal antecedent.

Acutely inflamed knee or another asymmetric lower-limb distribution: Peripheral phenotype.

Heel enthesitis, dactylitis, or inflammatory back pain: Spondyloarthritis context.

Ocular, genitourinary, and mucocutaneous features: Extra-articular support.

Infection precedes arthritis

Asymmetric lower-limb involvement

Enthesitis ± dactylitis

Extra-articular features possible

Slide 52 · Case application I: Postgenitourinary symptoms

A young adult recalls urethritis followed two weeks later by knee swelling and new eye redness. No symptoms from other organ systems are reported.

Which elements make the classical syndrome recognizable?

Clinical reasoning

Map the vignette to the triad and the timeline.

Discuss the temporal relationship, distribution, and extra-articular clues.

Slide 53 · Case I: Connect three clinical domains

Arthritis: The swollen knee.

Urogenital component: Preceding urethritis.

Ocular component: Conjunctival symptoms, compatible with the classical description.

Timing supports the postinfectious interpretation but is not a microbiologic diagnosis.

Arthritis

Urethritis / cervicitis

Conjunctivitis

Slide 54 · Case application II: A GI-triggered phenotype

A young adult develops acute swelling of one knee after a gastrointestinal illness. Examination reveals heel swelling at the Achilles insertion; Conjunctivitis is absent.

Does absence of conjunctivitis invalidate the syndrome?

Clinical reasoning

Use the expanded mono-/oligoarticular definition.

Discuss the temporal relationship, distribution, and extra-articular clues.

Slide 55 · Case II: The expanded definition matters

A preceding gastrointestinal infection supplies the relevant clinical context.

Monoarthritis plus Achilles enthesitis fits the described musculoskeletal phenotype.

The full classical triad is not mandatory under the broader Robbins description.

A precise causative organism cannot be deduced from the musculoskeletal findings alone.

Knee: Frequent arthritis

Heel: Frequent enthesitis

Digits: Possible dactylitis

Slide 56 · Case application III: Distinguish direct infection

An adult develops abrupt severe pain and swelling confined to one knee. No preceding GU or GI illness is recalled. The joint is very painful to move.

What high-consequence competing process needs attention?

Clinical reasoning

Why is postinfectious arthritis not assumed?

Discuss the temporal relationship, distribution, and extra-articular clues.

Slide 57 · Case III: Do not miss suppurative arthritis

A directly infected joint can present with sudden severe monoarthritis.

Joint aspiration yielding purulent fluid and the organism as diagnostic for suppurative arthritis.

Joint destruction can progress rapidly; Recognition and antimicrobial treatment are urgent.

The clinical vignette is deliberately insufficient to diagnose either condition.

Acute swollen joint

Direct joint infection must be considered

Rapid destruction in suppurative arthritis.

Slide 58 · Integrated teaching model

Trigger: Antecedent genitourinary or gastrointestinal infection.

Host context: Frequent HLA-B27 association within a spondyloarthropathy phenotype.

Inflammation: Peripheral joints, entheses, tendon sheaths, and sometimes axial structures.

Clinical course: Waxing and waning episodes, with frequent recurrence.

Preceding bacterial infection

Host immune response

Musculoskeletal inflammation

Detailed pathogenic antigens and cells remain uncertain

Slide 59 · Five practical recognition checks

Was there a relevant infection days to weeks earlier?

Is the arthritis acute, asymmetric, and predominantly lower-limb?

Are heel entheses or whole digits inflamed?

Are ocular, genitourinary, mucosal, skin/nail, or cardiac features present?

Could the joint instead be directly infected?

Infection precedes arthritis

Asymmetric lower-limb involvement

Enthesitis ± dactylitis

Extra-articular features possible

Slide 60 · Evidence boundaries of the Robbins subsection

No formal classification or diagnostic criteria set is supplied.

No reactive-arthritis-specific histologic photomicrograph or biopsy criteria are supplied.

The precise causative immune antigen and cellular pathway are not defined.

Management algorithms and laboratory sensitivity estimates are outside this supplied passage.

Do not present absent criteria, histology, or treatment regimens as textbook statements.

Slide 61 · Final clinicopathologic synthesis

Recognize an infection-associated asymmetric peripheral arthritis.

Localize associated heel symptoms to entheses and swollen digits to tendon-sheath synovitis.

Expect potential ocular, genitourinary, mucocutaneous, and axial manifestations.

Anticipate a fluctuating course; Distinguish direct joint infection when clinically plausible.

Infection precedes arthritis

Asymmetric lower-limb involvement

Enthesitis ± dactylitis

Extra-articular features possible

Slide 62 · References and source notes

Robbins, Cotran & Kumar: Pathologic Basis of Disease. 11th edition (2026). Chapter 26, “Bones, Joints, and Soft Tissue Tumors,” pp. 1091–1093.

Main subsection: “Reactive Arthritis,” p. 1092; adjacent sections: “Seronegative Spondyloarthropathies,” “Ankylosing Spondylitis,” and “Infectious Arthritis.”

Lecture statements are based on the provided Markdown transcription. The original textbook PDF pages and textbook images were not provided for direct verification.

Diagrams are original editable schematics; constructed clinical vignettes are teaching examples.