Which specific symptom differentiates reactive arthritis from other arthritic conditions?

The distinguishing characteristic of reactive arthritis is its association with a recent infection, typically following genitourinary or gastrointestinal infections. This linkage with an infectious trigger sets reactive arthritis apart from other forms of arthritis, such as osteoarthritis or rheumatoid arthritis, which may not have any preceding infectious event.

While joint swelling, stiffness, and pain at rest can be observed in various types of arthritis, they do not specifically indicate reactive arthritis alone. For example, joint swelling can occur in rheumatoid arthritis or gout, and morning stiffness is a hallmark of inflammatory types of arthritis but is not exclusive to reactive arthritis. Similarly, joint pain at rest can be encountered in a range of arthritic conditions. The unique association of reactive arthritis with recent infections is a key factor that aids in its diagnosis and differentiates it from other arthritic conditions.