Rheumatoid Arthritis Epidemiology

Rheumatoid Arthritis Epidemiology, hand deformity in rheumatoid arthritis
Hand deformity in rheumatoid arthritis. Image by James Heilman, MD, Wikimedia Commons, CC BY-SA 3.0.
Rheumatoid Arthritis Epidemiology, histopathology of a rheumatoid nodule
Histopathology of a rheumatoid nodule. Image by Mikael Häggström, M.D. Author info – Reusing images- Conflicts of interest: None Mikael Häggström, M.D.Consent note: Consent from the patient or patient’s relatives is regarded as redundant, because of absence of identifiable features (List of HIPAA identifiers) in the media and case information (See also HIPAA case reports guidance)., Wikimedia Commons, CC0.

Definition

  • Chronic symmetrical polyarthritis of unknown origin

Epidemiology

  • Worldwide distribution & affects all races & ethnic groups
  • Most common inflammatory arthropathy
    • 3% of population
    • M:F – 1:3
    • Annual incidence of 2-4/ 10 000 adult population
  • Peak age 4th-6th decade
    • Peak onset 40 years
  • Increasing in West
  • Life span ↓ 3-18 years

Aetiology

  • Unknown cause
  • Cell mediated immune response
  • Postulated combination of genetic susceptibility & environmental trigger
  • External trigger
    • ? Infection
    • Viral aetiology suggested due to synovitis similar to RA in patients with
    • Abnormal immune response in RA patients to EBV
    • Mycobacteria & Lyme disease related but no bacteria isolated from the joints in septic arthritis
    • Can induce arthritis in rats with immunisation with
      • Streptococcal cell walls
      • Soluble type II collagen
      • Freunds adjuvant
  • Genetic susceptibility
    • Associated with HLA DR4
    • 80% of patients with RA are HLA DW4 and/ or D4 positive
    • Concordance amongst identical twins is 30%
    • Some large series suggest incidence of RA in first degree relatives twice that of chance alone
  • Exogenous agent alters IgG to become antigenic
  • Helper T cells activate B Cells to become plasma cells
  • Plasma Cells produce Rheumatoid Factors (IgM usually) directed against IgG
  • Synovium acts as lymphoid organ
    • Local helper T cells activated
    • Local plasma cells produce RF
  • Antibody-Antiglobulin complexes formed
    • Stimulates complement
  • Secondary destructive inflammatory cascade
  • Rheumatoid Factor
  • Antiglobulin directed at Fc region of IgG
    • Production of antigens on surface of IgG suggested to be due to infective or other trigger
  • Usually IgM but heterogeneous
    • Can be IgM, IgG, IgA or IgE
  • Seen in 80% with Rheumatoid Arthritis
  • Incidence of RF positivity ↑ with duration of active synovitis
  • Correlation with
    • Long standing disease
    • Sustained activity
    • Nodules
    • Erosions
    • Extraarticular manifestations
  • ? Role in pathogenesis
  • Synthesised locally in subsynovial tissue & demonstrable in plasma cell by immunofluorescence & as eosinophilic bodies on H & E (Russell Bodies)
  • Synovium thus acts as lymphoid tissue like spleen & lymph nodes
  • Detected with Latex Agglutination
    • Use latex particles with human IgG adsorbed to surface
    • Various dilutions of test sera to agglutinate the complexes
    • Titre is highest dilution that agglutinates
    • 1:80 is positive
  • High Titre » Severe Disease
  • May also be present in
    • Elderly (incidental)
    • Infection
    • Autoimmune Disease
    • Chronic liver disease
    • Multiple Myeloma & other Lymphoproliferative disorders (5-10%)

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.