Ankle arthritis in a 6-year-old boy after a tick bite - a case report

Monoarthritis of the ankle is a rare condition in children, and is most often caused by a bacterial infection. Lyme disease is endemic in southern Scandinavia, and diagnosis remains a challenge. The clinical presentation of Lyme disease varies greatly, and often with considerable delay between exposure and presentation.

We report a case of ankle arthritis in a boy who presented one year earlier with a tick bite on the dorsum of the foot. He was suboptimally treated with oral antibiotics for one week, and developed in the following months a painless limp. Radiographs revealed a severe arthritis of the right ankle joint with necrosis of the talus and deformation of the talocrural and subtalar joints. There was no history of malaise, fever or other systemic symptoms. He remains seronegative for antibodies against B. burgdorferi.

The suboptimal oral antibiotic treatment may have hindered the antibody production against B burgdorferi, while not being therapeutic, resulting in severe ankle arthritis due to seronegative Lyme disease.