Reactive Arthritis

Reactive arthritis (ReA) is an immune-mediated spondyloarthropathy that begins acutely (eg, 1-4 weeks) after certain antecedent gastrointestinal (eg, Shigella) or genitourinary (Chlamydia trachomatis) infections.  ReA presents with inflammatory asymmetric mono- or oligoarthritis and sterile synovitis of the large joints (eg, knee, ankle) and axial spine (eg, back, sacroiliac joint).  Extraarticular manifestations (eg, conjunctivitis, uveitis, urethrits, skin findings) may also be present.  However, only a small proportion of patients have a classic triad of urethritis, arthritis, and conjuctivitis (formerly known as Reiter syndrome).

Although the precise mechanisms are unclear, ReA appears to result from an overactive T-cell–mediated immune response to the triggering bacterial infection.  In a process known as molecular mimicry, these activated T cells appear to cross-react with self antigens present in the synovial lining (leading to synovial thickening and fluid accumulation) as well as in other tissue (eg, skin, eye).