<aside>

Reactive arthritis is a seronegative spondyloarthropathy characterized by an asymmetric sterile arthritis developing 1–4 weeks after an infection (usually GI or genitourinary).

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https://www.youtube.com/watch?v=tnojIbJ-onw

https://youtu.be/ZzWtNKPdUdc

https://www.youtube.com/watch?v=snjGL2x6Eus

https://www.youtube.com/watch?v=8ouRZf2IJMk

https://www.youtube.com/watch?v=_mVlosOqRcY

Epidemiology

• Age: Young adults (20–40 years).
• Male > female (especially post-GU infection).
• Incidence: ~0.1–1% after triggering infections.
• Strong association with HLA-B27 (~50–80%).

Etiopathogenesis

<aside>

The disorder is due to an aberrant autoimmune response to the gastrointestinal/genitourinary infection caused by salmonella, shigella, campylobacter, or chlamydia.

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• Autoimmune mechanism: Molecular mimicry between bacterial antigens and host joint tissues.
• Synovial fluid sterile (no direct bacterial invasion).

Triggered by infection:

• GU: Chlamydia trachomatis (most common).
• GI: Salmonella, Shigella, Yersinia, Campylobacter.