Clinical meaning
Reactive arthritis is inflammatory arthritis developing after infection elsewhere in the body, typically genitourinary or gastrointestinal. The immune system activated against the infection cross-reacts with joint tissues through molecular mimicry. It appears 1-4 weeks after the triggering infection, primarily affecting large joints of the lower extremities. The classic triad is arthritis, urethritis, and conjunctivitis. It is associated with the HLA-B27 gene and is more common in young adults. Most cases resolve within 3-12 months, but some develop chronic arthritis.
Exam relevance
Risk factors: - Recent GU infection (especially Chlamydia) - Recent GI infection (Salmonella, Shigella, Campylobacter) - HLA-B27 positivity - Male sex (post-venereal form) - Young adult age (20-40 years) - Sexually active with multiple partners
Diagnostics: - Joint assessment: swelling, warmth, tenderness, ROM - ESR and CRP (elevated) - Urinalysis and Chlamydia NAAT - Eye examination for conjunctivitis or uveitis - X-rays of affected joints - Synovial fluid analysis if aspirated