Reactive arthritis and post-infectious inflammatory syndromes: Case

A nine-year-old boy is brought to the paediatric clinic by his parents, who have noticed a swollen right knee and a swollen left ankle for the past five days. Three weeks earlier, the family returned from a camping trip during which the boy had three days of bloody diarrhoea and abdominal cramps that resolved without the antibiotics. He is now afebrile and well, and he limps with a stiff gait that is worse in the morning and improves through the day. On examination the right knee and the left ankle are swollen, warm and restricted, the right heel is tender at the Achilles tendon insertion, and the right great toe is a puffy sausage digit. The joint aspirate from the right knee shows the white cell count of twelve thousand per microlitre with the negative gram stain and culture. The HLA-B27 is positive, the C-reactive protein is mildly raised, and the antinuclear antibody and the rheumatoid factor are negative. The stool culture is negative, but the Campylobacter serology is consistent with the recent infection.