Lyme Arthritis

Slide 1 · Lyme Arthritis

An inflammatory joint manifestation of Borrelia infection

Organism • Immune response • Synovial morphology • Diagnostic reasoning

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · What this lecture should establish

Link Ixodes-borne Borrelia infection to delayed joint disease

Explain inflammatory mechanisms and synovial morphology

Recognize the typical clinical joint pattern

Interpret serology, synovial PCR, and persistent arthritis cautiously

Slide 3 · Lyme arthritis is part of systemic infection

Tick-associated infection

Early skin disease

Organ dissemination

Late joint inflammation

Joint disease is one manifestation of a multisystem, stage-dependent infection.

Slide 4 · Infection and arthritis are not interchangeable

Lyme disease

Infection may produce skin, neurologic, cardiac, or musculoskeletal involvement.

Lyme arthritis

A late inflammatory joint manifestation with a characteristic large-joint pattern.

Slide 5 · Borrelia burgdorferi is the principal US agent

ORGANISM

Borrelia are slender, helical spirochetes.

B. Burgdorferi is the major Lyme disease agent in the United States.

The infectious organism initiates a host inflammatory response.

The joint disease is not defined by direct visualization of bacteria.

Slide 6 · Geographic species differ

Region

Lyme-associated species

United States

B. Burgdorferi

Europe and Asia

B. Burgdorferi, B. Afzelii, B. Garinii

These are textbook geographical associations, not an exhaustive species taxonomy.

Slide 7 · Ixodes ticks connect animal reservoirs to humans

Rodents / birds

Ixodes tick

Human exposure

Borrelia infection

Rodents as reservoirs and birds particularly for B. Garinii.

Slide 8 · Endemic settings guide suspicion

EPIDEMIOLOGIC CONTEXT

US disease is concentrated in the Northeast and upper Midwest.

Chapter 26 emphasizes New England and the mid-Atlantic region.

The geographic distribution is expanding.

Geographic exposure supports, but cannot by itself establish, the diagnosis.

Slide 9 · Lyme disease has successive clinical phases

Early localized

Dermal infection; Erythema migrans

Early disseminated

Secondary skin, neurologic, cardiac, and musculoskeletal manifestations

Late disseminated

Chronic inflammatory arthritis; Selected neurologic manifestations

Slide 10 · Early localized infection begins in the dermis

Infected tick bite

Spirochetal multiplication

Dermal inflammation

Expanding erythema migrans

Slide 11 · Erythema migrans is an early clinical clue

EARLY LOCALIZED STAGE

An expanding erythematous lesion develops at the inoculation site.

A pale center may occur; The appearance is not required to be target-shaped.

Erythema migrans in approximately 80% of patients.

Fever and lymphadenopathy may accompany the lesion.

Slide 12 · Early dissemination involves several tissues

Initial skin focus

Hematogenous spread

Cranial nerves / meninges

Heart / other skin sites

Joint or muscle pain may also occur during dissemination.

Slide 13 · Migratory pain does not equal established arthritis

Early musculoskeletal manifestations

Migratory joint and muscle pain during dissemination.

Late inflammatory arthritis

Clinical episodes of synovitis that may last weeks to months.

Slide 14 · Late disease may emerge months after exposure

Exposure

Ixodes-borne infection

Weeks

Early local and disseminated findings

Months later

Late large-joint inflammatory arthritis

Conceptual sequence; Timing is variable and is not a diagnostic clock.

Slide 15 · Why early treatment changes arthritis frequency

Pattern

Clinical course

Treated earlier

Progression to arthritis is now uncommon account.

Without timely treatment

Migratory/persistent inflammatory arthritis becomes substantially more common.

Slide 16 · Treated and untreated cohorts

<10%

Arthritis in current Borrelia infections, as described in Ch. 26

Up to 80%

Migratory arthritis with delayed/absent timely treatment

Textbook cohort-context estimates; They are not individual prognostic probabilities.

Slide 17 · Large joints dominate the arthritis phenotype

01

Knee

02

Shoulder

03

Elbow

04

Ankle

Listed in descending order of frequency.

Slide 18 · Knee involvement is the characteristic clue

CLINICAL PATTERN

Large-joint synovitis is typical.

The knee is most frequently involved.

A swollen knee after compatible exposure should trigger diagnostic consideration.

The finding is suggestive, not pathognomonic.

Slide 19 · Usually few joints are active at once

DISTRIBUTION

Initial attacks often involve one or two joints.

Joint disease can recur at another anatomical site.

A limited joint count does not exclude a systemic infection.

The pattern contrasts with a symmetric small-joint inflammatory polyarthritis.

Slide 20 · Arthritis can move between sites over time

Initial episode

Inflammation in one or two joints

Intervening period

Symptoms may vary

Subsequent episode

Another large joint may become involved

The schematic indicates anatomical migration, not spread by direct contact between joints.

Slide 21 · Individual attacks may last weeks to months

TEMPORAL PATTERN

The initial episode can be prolonged.

Attacks lasting weeks to months.

Symptoms may recur or appear in different joints.

Duration must be interpreted with clinical and laboratory evidence.

Slide 22 · Symptom patterns change as infection evolves

Stage

Musculoskeletal presentation

Early disseminated

Migratory arthralgia and myalgia

Late disseminated

Arthritis of one or a few large joints

Late severe disease

Potential cartilage damage

Slide 23 · Systemic history links an arthritic knee to Lyme

A patient from an endemic region has recurrent swelling of a knee.

Several months earlier, they recall an expanding erythematous rash.

They have no evidence supplied here of an identified organism in joint fluid.

What elements raise suspicion for Lyme arthritis?

Slide 24 · Case analysis: Combine pattern and exposure

CLINICOPATHOLOGIC REASONING

Endemic geographic context increases pretest suspicion.

A compatible earlier skin lesion places the joint disease in a systemic timeline.

Recurrent large-joint synovitis matches the described phenotype.

The diagnosis still requires appropriate testing and exclusion of alternatives.

Slide 25 · The organism acts chiefly through host inflammation

Borrelia tissue infection

Innate immune recognition

Cytokine / T-cell response

Chronic synovitis

The chapter does not attribute the tissue injury to Borrelia exotoxin or endotoxin.

Slide 26 · Direct bacterial toxins are not the explanation

Not the stated mechanism

B. Burgdorferi is not described as producing damaging endotoxins or exotoxins.

Dominant proposed mechanism

Inflammation produced by the host response to microbial antigens.

Slide 27 · Borrelial lipoproteins activate innate sensors

Borrelial lipoproteins

TLR1 / TLR2

Macrophage activation

Inflammatory mediators

Slide 28 · Macrophage cytokines amplify local inflammation

Activated macrophages

IL-6 and TNF

Inflammatory recruitment

Tissue response

These molecules are mechanistic mediators, not diagnostic biomarkers in this source.

Slide 29 · Innate killing can be incomplete

Innate recognition

Reactive nitrogen intermediates

Partial bacterial killing

Possible persistence

Innate responses often reduce but do not eliminate infection.

Slide 30 · T cells contribute to inflammatory lesions

ADAPTIVE-CELL RESPONSE

The text implicates T cells and cytokines in lesion formation.

CD4-positive T cells are prominent in affected synovium.

The resulting lesion is chronic, cell-rich synovitis.

Histology reflects immune activation rather than a toxin-mediated necrosis.

Slide 31 · Specific antibody responses arise after infection

Infection begins

Borrelia establishes infection

2–4 weeks

Borrelia-specific antibodies emerge

Later response

Antibody and complement support clearance

The 2–4-week interval is quoted as the textbook antibody-response timeline.

Slide 32 · Antibody facilitates phagocytosis and killing

Anti-Borrelia antibody

Complement engagement

Phagocytosis

Bacterial killing

Slide 33 · Immune evasion helps explain persistence

Antibody pressure

Host recognition targets expressed surface antigens.

Spirochetal evasion

Antigenic variation and alteration of surface-protein expression reduce immune recognition.

Slide 34 · Outer surface protein C changes during infection

OSPC

Outer surface protein C supports establishment of infection.

Its expression is not required for persistence.

Downregulation is described as one way Borrelia evades antibody responses.

Distinguish this mechanism from the separate VlsE antigenic-variation system.

Slide 35 · VlsE variation creates shifting antigenic targets

VlsE expression cassette

Alternative coding sequences

Changed surface antigen

Immune escape

One expressed VlsE antigenic variant is replaced by another: Antibody recognition can be evaded.

Slide 36 · Two paths connect infection to lasting synovitis

Persistent infection-related immune activation

Ongoing interaction between Borrelia antigens and host defenses.

Proposed postinfectious autoimmunity

Cross-reactive immune responses continue after bacterial detection is lost.

Slide 37 · Autoimmune cross-reactivity remains a hypothesis

UNRESOLVED MECHANISM

Molecular mimicry as a proposed mechanism.

An antibody/T-cell response to outer surface protein A is implicated in the hypothesis.

The corresponding self antigen(s) are unidentified in the excerpt.

Do not teach cross-reactivity as a proven universal cause of persistent arthritis.

Slide 38 · Lyme synovitis has a characteristic morphologic set

1

Lining-cell hyperplasia

2

Villous synovial hypertrophy

3

Mononuclear infiltrate

4

Vascular onion-skin thickening

Slide 39 · Normal synovium provides a morphology baseline

Thin synovial lining

Subsynovial stroma

Synovial vascular supply

Simplified schematic of synovial compartments; Not a tissue section.

Slide 40 · Villous synovial hypertrophy increases surface folds

Villous projection

Thickened synovial lining

Inflammatory stromal cells

Schematic tissue architecture, not a specimen.

Slide 41 · Synoviocyte hyperplasia thickens the lining

LINING RESPONSE

Reactive hyperplasia produces additional synovial lining cells.

The lining becomes conspicuous and enlarged.

It coexists with villous changes and chronic inflammation.

It is not specific for Lyme arthritis in isolation.

Slide 42 · The infiltrate is predominantly mononuclear

Lymphocytes

Plasma cells

CD4-positive T cells

Conceptual cell roster; No microscopic identification is implied.

Slide 43 · Fibrin accompanies the chronic synovitis

MATRIX CHANGE

The joint-section morphology includes fibrin deposition.

It accompanies synovial hyperplasia and inflammatory infiltrates.

The finding belongs to the combined pattern of synovial inflammation.

Fibrin alone cannot identify Borrelia infection.

Slide 44 · Obliterative endarteritis is a distinctive clue

Lumen

Concentric vascular wall thickening

Narrowed arteriolar lumen

Onion-skin–like pattern

Schematic of reported arteriolar lesion; Not histology.

Slide 45 · Onion-skin arteriolar walls require contextual reading

VASCULAR PATHOLOGY

Concentric thickening of arteriolar walls.

The lumen may be compromised by obliterative endarteritis.

Comparable concentric vascular lesions can occur in other disorders.

Interpret vascular morphology with the complete synovial picture.

Slide 46 · Early morphology can resemble rheumatoid synovitis

Finding

Lyme arthritis

Rheumatoid arthritis

Synovial lining

Hyperplasia

Hyperplasia may occur

Infiltrate

Mononuclear; CD4 T cells prominent

Chronic inflammatory cells

Arterioles

Onion-skin–like thickening noted

Not the defining RA lesion

Comparison is conceptual; No single feature independently establishes disease identity.

Slide 47 · Late disease can erode cartilage

Protracted synovial inflammation

Joint-tissue injury

Cartilage surface erosion

Potential structural damage

Extensive large-joint cartilage erosion in late disease.

Slide 48 · Severe cases can mimic rheumatoid arthritis

PITFALL

The histopathologic resemblance may be striking.

Synovial hypertrophy and mononuclear inflammation overlap.

The disease context and joint distribution help separate diagnoses.

Morphology alone should not be assigned etiologic specificity it lacks.

Slide 49 · Clinical swelling is the tissue-level outcome

Lining hyperplasia

Stromal inflammatory infiltrate

Synovial expansion / irritation

Symptomatic arthritis

This is an explanatory synthesis of the described morphological pattern.

Slide 50 · Diagnosis integrates phenotype and laboratory evidence

Compatible arthritis

Exposure / disease history

Anti-Borrelia serology

Integrated interpretation

Slide 51 · Anti-Borrelia serology is the principal test

DIAGNOSTIC PRINCIPLE

Diagnosis is usually serologic.

The test detects the host antibody response to Borrelia.

A positive antibody result requires compatible clinical interpretation.

The excerpt does not specify a contemporary testing algorithm.

Slide 52 · PCR detects Borrelia DNA in synovial fluid

≈70%

Synovial-fluid PCR detection described for patients with Lyme arthritis

Not stand-alone

The textbook nevertheless presents serology as the usual diagnostic basis

PCR performance is source-specific and should not be generalized to every specimen or population.

Slide 53 · A negative PCR is not an absolute exclusion

What PCR measures

Nucleic acid from Borrelia in the tested joint sample.

What it cannot by itself resolve

The entire clinical state, including immune-driven inflammation or test limitations.

Interpretive teaching inference; Synovial PCR is an adjunct, not the source-preferred stand-alone diagnostic test.

Slide 54 · Consider alternative causes of monoarthritis

Disorder

Distinguishing contextual clue

Acute bacterial septic arthritis

Abrupt painful swollen joint; Organism may be demonstrated in aspirate

Mycobacterial arthritis

Indolent, often destructive, granulomatous process

Lyme arthritis

Endemic exposure; Episodic large-joint synovitis; Serology

Acute septic arthritis requires prompt clinical assessment; Do not defer evaluation based on presumed Lyme disease.

Slide 55 · Viral arthritis can have a different time course

Viral arthritis

Chapter 26 describes acute-to-subacute joint disease with several viral infections.

Lyme arthritis

The source emphasizes prolonged/recurrent large-joint inflammatory attacks.

Neither duration nor distribution alone is definitive.

Slide 56 · Rheumatoid arthritis is a major pathologic mimic

Feature

Lyme arthritis

Rheumatoid arthritis

Pattern

One or a few large joints

Often begins in small joints of the hands

Mechanism

Infection-associated immune response

Autoimmune synovial inflammation

Microscopy

Chronic synovitis; Vascular onion-skin change

Inflammatory pannus / destructive synovitis

Slide 57 · Osteoarthritis has a different primary lesion

Feature

Lyme arthritis

Osteoarthritis

Primary problem

Inflammatory synovitis

Mechanical cartilage degeneration

Joint disease

Episodic large-joint swelling

Degenerative weight-bearing joint changes

Morphology

Cell-rich chronic synovitis

Cartilage fibrillation; Osteophytes; Sclerosis

Slide 58 · Synovial biopsy is pattern recognition, not proof

PATHOLOGY REPORTING

Identify lining hyperplasia and chronic mononuclear infiltrates.

Look for fibrin and onion-skin arteriolar lesions.

Recognize overlap with rheumatoid and other chronic synovitides.

Use the clinical and laboratory framework to support etiology.

Slide 59 · Antibiotics are effective in most Lyme arthritis

≈90%

Curative treatment response to antibiotics active against Borrelia, per Robbins

Residual cases

Persistent joint inflammation is described as uncommon

The textbook section does not provide drug regimens or treatment durations.

Slide 60 · Postinfectious arthritis may persist after therapy

Documented Lyme arthritis

Appropriate antibiotic treatment

Persistent joint inflammation

Postinfectious / antibiotic-refractory category

These labels for an uncommon persistence scenario.

Slide 61 · Post-treatment synovial PCR is often negative

POSTINFECTIOUS DISEASE

The text notes that Borrelia frequently cannot be detected in these cases.

Negative detection may persist even with PCR.

Persistent arthritis therefore does not automatically demonstrate ongoing detectable infection.

The proposed immune mechanism remains incompletely defined.

Slide 62 · Separate observation from the proposed explanation

Status

What can be said

Observed

Some arthritis persists after antibiotics; PCR is often negative.

Proposed mechanism

Cross-reactive immune responses to OspA and unknown self-antigens.

Not established by excerpt

An obligatory autoimmune pathway for all persistent arthritis.

Slide 63 · Persistent swelling is a diagnostic reasoning problem

A person with previously diagnosed Lyme arthritis received antibiotic treatment.

The knee remains inflamed despite completion of therapy.

Repeat synovial-fluid PCR does not detect Borrelia DNA.

What can and cannot be inferred from this pattern?

Slide 64 · Case analysis: Postinfectious is not a synonym for active infection

INTERPRETIVE DISCIPLINE

Persistent clinical synovitis is the observation.

The negative PCR reduces evidence for detectable organisms in the sampled joint.

An immune-mediated explanation in some cases.

Neither a pathogen-free state nor active infection is proven by symptoms alone.

Slide 65 · Pathology–clinical integration: Four checkpoints

Is the joint distribution consistent with large-joint Lyme arthritis?

Does the exposure and systemic disease chronology fit?

Are Borrelia antibodies and other findings interpreted appropriately?

Could another cause of arthritis explain the presentation?

Slide 66 · Five defining facts to retain

Ixodes-transmitted Borrelia initiates the disease.

Early systemic infection can precede delayed synovitis.

One or a few large joints—especially the knee—are typically involved.

Synovitis includes lining hyperplasia, mononuclear cells, and arteriolar change.

Serology is central; PCR and post-treatment persistence require interpretation.

Slide 67 · Sources and image integrity

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026). Chapter 26: Lyme Arthritis, pp. 1093–1094.

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. (2026). Chapter 8: Lyme Disease, pp. 344–345.

Constructed illustrations are editable conceptual diagrams, not patient specimens or reproduced histology.