What are the causes of reactive arthritis?

Causes of Reactive Arthritis

Reactive arthritis is primarily caused by specific bacterial infections of the urogenital, gastrointestinal, or respiratory tracts, with the most common pathogens being Chlamydia trachomatis, Yersinia, Salmonella, Shigella, and Campylobacter. 1

Primary Infectious Triggers

Genitourinary Tract Infections

• Chlamydia trachomatis - most common urogenital trigger 1
• Chlamydia pneumoniae - less frequent than C. trachomatis 1

Gastrointestinal Tract Infections

• Enterobacteria including:
  • Yersinia enterocolitica 2
  • Salmonella species 1
  • Shigella species 1
  • Campylobacter species 1
• Clostridium difficile - less commonly recognized but documented cause 3

Respiratory Tract Infections

• Mycoplasma pneumoniae 2
• Chlamydia pneumoniae 2

Pathophysiological Mechanism

Reactive arthritis is characterized by:

1. Sterile joint inflammation - No viable bacteria can be cultured from the joint, distinguishing it from septic arthritis 1
2. Bacterial components in joints - Despite being culture-negative, pathogen components (antigens or DNA) are frequently detectable in affected joints 1
3. Post-infectious immune response - Occurs after a symptom-free interval following the triggering infection 2
4. Genetic predisposition - Strong association with HLA-B27 (present in approximately 50% of cases) 1, 4

Key Distinguishing Features from Other Arthritides

• Timing: Typically occurs 10 days after the triggering infection, unlike rheumatic fever which occurs 14-21 days post-streptococcal infection 2
• Pattern: Usually presents as asymmetric oligoarthritis primarily affecting lower limb joints 5
• Response to treatment: Does not respond readily to acetylsalicylic acid, unlike rheumatic fever arthritis 2
• Duration: Can be persistent and cumulative rather than migratory and transient 2
• Joint involvement: Can affect large joints, small joints, or the axial skeleton 2

Clinical Presentation

Typical manifestations include:

• Monoarticular or oligoarticular peripheral arthritis (commonly affecting knees or ankles) 1
• Dactylitis (sausage digits) 5
• Sacroiliitis and axial involvement in some cases 5
• Extra-articular manifestations:
  • Conjunctivitis 4
  • Circinate balanitis 4
  • Skin rash, including pustular lesions on plantar areas 5
  • Enthesitis (inflammation at tendon/ligament insertions) 5

Common Pitfalls in Diagnosis

1. Missing the triggering infection: The interval between the initial infection and arthritis development may lead to failure in connecting the two events
2. Confusing with other arthritides: Symptoms may overlap with other inflammatory joint conditions
3. Over-reliance on HLA-B27: While associated with reactive arthritis, it's present in only about 50% of cases 1
4. Assuming all post-infectious arthritis is reactive arthritis: Poststreptococcal reactive arthritis differs from classic reactive arthritis in its triggers and clinical course 2

Epidemiology

• Estimated prevalence: 40 per 100,000 population 1
• Estimated incidence: 5 per 100,000 population 1
• Disease course is typically self-limiting, but up to 20% of patients may experience a chronic course lasting more than one year 6

Understanding the specific infectious trigger is essential for appropriate management, as treatment approaches may differ based on the causative pathogen, particularly for Chlamydia-induced reactive arthritis where antibiotics may be beneficial 6.