Reactive arthritis and post-infectious inflammatory syndromes: Viva

Opening question

Examiner: A nine-year-old boy limps into your emergency department with a swollen right knee and a swollen left ankle. He had a bout of bloody diarrhoea on a camping trip three weeks ago. Walk me through how you frame this problem. ^[4]

Candidate: My first frame is the safety frame. The acute swollen joint in a child is septic arthritis until proven otherwise, so I assess the fever, the systemic wellness, the ability to bear weight and the Kocher criteria, and I aspirate any hot joint that raises the suspicion. Once the sepsis is excluded, the second frame is the post-infectious frame. The one-to-four-week latency after the gastrointestinal infection, the asymmetric lower-limb oligoarthritis, the enthesitis at the Achilles tendon and the dactylitis of the great toe point to the reactive arthritis on the spondyloarthritis spectrum. The three-week latency after the bloody diarrhoea is the anchor. ^[4][9]