Lessons of the month 2: Tubercular osteomyelitis of the knee involving the growth plate in a young girl mimicking oligoarticular juvenile idiopathic arthritis.

Oligoarticular juvenile idiopathic arthritis (JIA) and tubercular arthritis in children can present in a similar way as monoarthritis. Patients with musculoskeletal tuberculosis may not have the classical constitutional symptoms. Moreover, microbiological evidence of infection may not be found in all patients. In such cases, features on imaging aid in the diagnosis. We present a case of an 8-year-old girl who had inflammation in the right knee. Investigations showed negative results for autoimmune markers. Synovial fluid examination did not reveal any evidence of tuberculosis. However, magnetic resonance imaging of the knee joint showed inflammation around the distal growth plate of the femur, away from the knee joint. The suspicion of tuberculosis was strengthened by the presence of left hilar lymphadenopathy on chest X-ray and positive result on tuberculin skin sensitivity test. The patient showed remarkable clinical and radiological recovery with anti-tubercular therapy. Peculiar features on imaging may help in differentiating infections from inflammatory arthritides, even in the absence of microbiological evidence of infection. © Royal College of Physicians 2022. All rights reserved.