Tuberculous arthritis is difficult to diagnose early because of its atypical insidious clinical manifestations and non-specific imaging findings. Specifically, monoarticular tuberculosis of the knee may mimic pigmented villonodular synovitis (PVNS). The present report describes a young patient with tuberculous arthritis of the knee. Proper diagnosis was delayed due to magnetic resonance imaging findings, such as hemosiderin deposits and a nodular mass around the knee joint, suggesting the diffuse type of PVNS. These findings suggest that the first step in the diagnosis of tuberculous knee arthritis is to have a high index of suspicion.
Level of evidence: IV.