What Is Rheumatoid Arthritis: Causes, Symptoms, and Treatment Options

This article is for informational purposes only. Consult a qualified healthcare professional for medical advice, diagnosis, or treatment.

What Is Rheumatoid Arthritis?

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease characterized by persistent inflammation of the synovial joints — the flexible joints lined with a synovial membrane. Unlike osteoarthritis, which results from mechanical wear and tear, RA arises when the immune system mistakenly attacks the body's own joint tissues, leading to pain, swelling, stiffness, and progressive joint destruction. Left untreated, RA can erode cartilage and bone, causing permanent deformity and functional disability. RA affects approximately 1% of the global population — around 18 million people worldwide — and is roughly two to three times more common in women than in men. Onset typically occurs between the ages of 30 and 60, though the disease can develop at any age.

Causes and Risk Factors

The precise cause of RA remains incompletely understood, but it involves a complex interplay of genetic predisposition, environmental triggers, and immune dysregulation.

Genetic Factors

The strongest genetic risk factor is the HLA-DRB1 gene, specifically alleles encoding the "shared epitope" — a conserved amino acid sequence in the peptide-binding groove of HLA-DR molecules. These alleles are present in approximately 70% of RA patients versus 30% of the general population. Other genes implicated include PTPN22, STAT4, and CTLA4, which all modulate T- and B-cell activation.

Environmental Triggers

• Smoking: The strongest modifiable risk factor. Smoking increases RA risk by 2–4 fold and is associated with anti-citrullinated protein antibody (ACPA)-positive RA. It is thought to promote citrullination of proteins in the lung, generating neoantigens.
• Oral microbiome: Porphyromonas gingivalis, a bacterium associated with periodontitis, expresses citrullinating enzymes and may initiate the autoimmune response in genetically susceptible individuals.
• Hormonal factors: Female predominance, improvement during pregnancy, and postpartum flares suggest sex hormones modulate disease activity.
• Silica exposure: Occupational silica dust inhalation is associated with increased RA risk in several cohort studies.

Pathophysiology: How RA Damages Joints

In RA, autoreactive T cells (particularly CD4+ Th1 and Th17 cells) recognize citrullinated self-antigens presented by HLA-DR molecules on antigen-presenting cells within the synovium. This triggers B cell activation and the production of autoantibodies — most notably rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA/anti-CCP). These autoantibodies form immune complexes that deposit in joint tissue, activating complement and recruiting macrophages and neutrophils.

The inflamed synovial membrane (synovitis) thickens into a highly vascularized, invasive tissue called pannus. Pannus secretes destructive enzymes (matrix metalloproteinases) and pro-inflammatory cytokines — especially tumor necrosis factor-alpha (TNF-α), interleukin-1 (IL-1), and interleukin-6 (IL-6) — that progressively erode underlying cartilage and bone.

Signs and Symptoms

The classic joint distribution in RA is symmetric and preferentially involves the metacarpophalangeal (MCP) joints, proximal interphalangeal (PIP) joints, and metatarsophalangeal (MTP) joints. Cervical spine involvement (particularly atlantoaxial subluxation) can occur in long-standing disease and poses surgical risk.

Diagnosis

The 2010 ACR/EULAR classification criteria for RA assign points based on joint involvement, serology, inflammatory markers, and symptom duration. A score of ≥6/10 classifies definite RA:

• Serology (up to 3 points): Low-positive RF or ACPA (2 pts); high-positive RF or ACPA (3 pts)
• Joint involvement (up to 5 points): From 1 large joint (0 pts) to >10 small joints (5 pts)
• Acute-phase reactants (1 point): Abnormal CRP or ESR
• Duration of symptoms (1 point): ≥6 weeks

Imaging with X-ray, ultrasound, or MRI can reveal joint erosions, synovitis, and effusions. Anti-CCP antibodies have approximately 95% specificity for RA and may appear years before clinical symptoms.

Treatment

The treat-to-target (T2T) strategy — aiming for clinical remission or low disease activity — has transformed RA outcomes. Early aggressive treatment with methotrexate, followed by combination therapy or biologics if the target is not reached within 3–6 months, substantially reduces structural damage and improves long-term function. With modern therapy, many patients achieve remission and can maintain near-normal joint function.