Rheumatoid Arthritis

Definition and Overview

Epidemiology

• Prevalence: 0.5-1% in most developed countries; global age-standardized prevalence ~0.25% (Global Burden of Disease 2017).
• Regional variation: Highest in North America, Western Europe, and the Caribbean (0.3-0.4%); lowest in Southeast Asia and Sub-Saharan Africa (~0.1%).
• Special population: Native Americans (Pima and Chippewa tribes) have rates approaching 5-7%.
• Sex ratio: ~3:1 female predominance.
• Peak onset: 4th-5th decade, though it can occur at any age.

Pathogenesis

Genetic Risk Factors

Pre-Clinical Phase

• In seropositive unaffected first-degree relatives of RA patients, subclinical mucosal inflammation is demonstrable
• RA-related autoantibodies occur in diseases characterized by mucosal inflammation (e.g., bronchiectasis)
• ACPA specificity expands in a time-dependent manner pre-clinically, peaking at symptom onset

Citrullination and ACPAs

• Citrullination is a post-translational modification converting positively charged arginine to neutral citrulline, catalyzed by peptidylarginine deiminase (PAD) enzymes (PAD2, PAD4).
• In genetically predisposed individuals, citrullinated proteins trigger autoimmunity.
• Anti-citrullinated protein antibodies (ACPAs) target: collagen type II, fibrinogen, vimentin, and α-enolase.
• The interaction of HLA-DRB1 shared epitope + smoking + periodontitis drives ACPA generation.

Role of Oral Microbiome

Synovial Pathology

• Fibroblast-like synoviocytes (FLS) are activated, producing pro-inflammatory cytokines (TNF, IL-1, IL-6) and matrix metalloproteinases leading to cartilage/bone destruction.
• FLS undergo epigenetic reprogramming (global DNA hypomethylation), acquiring an aggressive, invasive "inflammatory memory" phenotype.
• NETs (Neutrophil Extracellular Traps): Neutrophils are abundant in RA synovium and overexpress PAD2/PAD4. NETs activate FLS, releasing citrullinated autoantigens and perpetuating autoimmunity.

Autoantibodies and Complement

• Rheumatoid factor (RF): IgM (usually) against the Fc portion of IgG.
• ACPAs: More specific than RF; predict aggressive, erosive disease.
• Anti-carbamylated protein (anti-CarP) antibodies: Additional highly specific marker.
• Complement is activated primarily within the joint (via alternative and lectin pathways), with C3a, C5a, and MAC all contributing to synovial inflammation.
• Platelet activation: Thrombocytosis and platelet microparticles are markers of active RA; platelet-leukocyte aggregates, soluble P-selectin, and soluble CD40L are elevated.

Clinical Features

Articular Manifestations

• Symmetric polyarticular inflammatory arthritis involving the small joints of the hands and feet (MCPs, PIPs, wrists, MTPs)
• Prolonged morning stiffness (>1 hour) - cardinal feature
• Swelling, warmth, and tenderness of joints; "boggy" synovitis on exam
• Characteristic deformities (late disease): ulnar deviation at MCPs, swan-neck (PIP hyperextension, DIP flexion), Boutonniere deformity, Z-deformity of thumb
• Large joint involvement (knees, elbows, shoulders, ankles, hips) also occurs
• Cervical spine involvement: atlantoaxial subluxation - important perioperative concern
• Spares DIP joints (distinguishing from OA and psoriatic arthritis)

Extra-Articular Manifestations

Diagnosis and Classification

2010 ACR/EULAR Classification Criteria

Key Laboratory Tests

• RF (rheumatoid factor): Present in ~70-80%; not specific
• Anti-CCP (ACPA): ~70% sensitive, >95% specific; predicts erosive disease
• CRP, ESR: Markers of systemic inflammation
• CBC: Anemia of chronic disease, thrombocytosis
• Imaging: Plain X-rays (erosions, joint space narrowing); MRI/ultrasound more sensitive for early synovitis and subclinical inflammation

Disease Activity Measurement

Management

Principles (Treat-to-Target, T2T)

1. Target: Remission or low disease activity for all patients.
2. Monitor disease activity regularly and escalate therapy if target not met within 3-6 months.
3. The specific DMARD chosen is less important than consistently achieving the target - proven by the TICORA and Dutch BeSt studies.
4. RA can and should be diagnosed early; DMARD therapy should start at diagnosis.

The DMARD Toolbox

• Methotrexate (MTX): The anchor drug; cornerstone of therapy. Titrated up to 25 mg/week; subcutaneous route increases bioavailability. Always given with folic acid supplementation.
• Hydroxychloroquine (HCQ): Used in mild disease or combination (triple therapy with MTX + SSZ)
• Sulfasalazine (SSZ): Often used in combination
• Leflunomide: Alternative to MTX when MTX is contraindicated

• Tofacitinib, Baricitinib, Upadacitinib, Filgotinib
• Oral agents; note safety considerations regarding cardiovascular events and malignancy risk (post-marketing surveillance requirements)

Treatment Algorithm

1. First-line: MTX monotherapy (strongly recommended by ACR/EULAR). If MTX not tolerated, use leflunomide or sulfasalazine.
2. If MTX fails (inadequate response at 3 months, target not met by 6 months): Add a bDMARD or JAK inhibitor to MTX. Choice guided by presence of poor prognostic factors, comorbidities (e.g., avoid JAK inhibitors in high CV risk patients), cost, and patient preference.
3. If first bDMARD fails: Switch to another bDMARD (different mechanism) or tsDMARD.
4. Triple therapy (MTX + HCQ + SSZ) is a cost-effective alternative to bDMARDs in resource-limited settings.

Glucocorticoids

• Powerful, rapidly effective, but carry significant short- and long-term adverse effects.
• Use only as a bridge to DMARD therapy - not as monotherapy.
• Best chronic dose: zero. Always taper once DMARDs are effective.
• Low-dose prednisone (5-10 mg/day) added to MTX reduces disease activity and radiographic progression (CAMERA-II trial).

NSAIDs

• Provide symptom relief but are not disease-modifying.
• Never use without concurrent DMARDs.
• Discontinue once DMARDs achieve disease control.

Tapering and Remission

• DMARD tapering only considered in patients who have achieved sustained remission.
• Drug-free remission remains largely out of reach - at least one DMARD usually must be continued.

Monitoring and Comorbidities

• Cardiovascular risk assessment and management (statins, blood pressure control)
• Bone density monitoring and osteoporosis prevention (especially in glucocorticoid-treated patients)
• Lung disease surveillance (baseline PFTs and HRCT in appropriate patients)
• Infection risk assessment before biologic/JAK inhibitor therapy (TB screening, hepatitis B, live vaccine update)
• Malignancy screening (particularly lymphoma risk)

Prognosis

• RF and ACPA positivity predicts an aggressive disease course with erosive joint damage and extra-articular manifestations.
• Untreated or undertreated RA leads to substantial disability, reduced work capacity, and shortened lifespan.
• With modern T2T strategies and the full DMARD toolbox, the majority of newly diagnosed RA patients can achieve remission or low disease activity - a transformation from the pre-biologic era.