(en) A 9-year-old patient, complaining of pain and swelling of his left elbow for 3 months, was referred to the paediatric rheumatology consultation. On clinical examination, there was a local swelling with limited joint mobility of the left elbow. The other joints were normal. There were no associated skin lesions, weight loss, or fever. His personal and family medical history were not relevant. A blood test for inflammatory markers, complete auto-immune serology, and Borrelia serology were all normal. [...]