Knee tuberculosis masquerading as pigmented villonodular synovitis.

Tuberculosis (TB), once a disease confined to undeveloped or developing nations is currently in resurgence, which is attributable to pandemic human immunodeficiency virus (HIV) infection and immigration from endemic areas. Tuberculous arthritis is difficult to diagnose early because of its atypical insidious clinical manifestations and nonspecific imaging findings. TB is also known as the 'great mimicker'. Specifically, monoarticular tuberculosis of the knee may mimic pigmented villonodular synovitis (PVNS). The present report describes a young patient with tuberculous arthritis of knee joint. Accurate diagnosis and appropriate management was delayed due to magnetic resonance imaging (MRI) findings, such as, hemosiderin deposits and a nodular mass around the knee joint, suggestive of a diffuse type of PVNS. Our findings suggest that the first step in the diagnosis of tuberculous knee arthritis is to have a high index of suspicion.