Mycobacterium tuberculosis monoarthritis in a child

One-third of the world's population is infected with Mycobacterium tuberculosis and the global burden of tuberculosis continues to grow [1,2]. Approximately one-quarter to one-third of children with tuberculosis develop extrapulmonary involvement [3-5]. Skeletal tuberculosis, now rare since the advent of antituberculosis therapy, occurs in approximately 5% of children with extrapulmonary tuberculosis [3,4]. The vertebral body is the most common skeletal site involved followed by lower limb bones [5,6]. Rarely, intra-articular inflammation can occur in children either as a result of direct invasion of the tuberculous bacillus into the joint or as a consequence of an aseptic reactive arthritis (so-called Poncet's disease) related to an extra-articular tuberculous focus [3-20]. Intra-articular Mycobacterium tuberculosis infection is especially rare in children in the absence of associated pulmonary disease [7,8,13,14,17,19]. Consequently, delays in recognition and treatment of this diagnostically challenging condition occur.We report a child with isolated Mycobacterium tuberculosis monoarthritis who presented with features initially suggesting oligoarthritis subtype of juvenile idiopathic arthritis (JIA). The patient we present illustrates the need to maintain heightened awareness that tuberculosis joint infection can occur in high-risk populations even in the absence of overt pulmonary involvement.At age 2 years 10 months this previously healthy North American Indian girl presented with a 3-week history of left knee swelling and morning stiffness without associated symptoms. There were no infectious contacts reported at first presentation. On initial physical examination, the left knee was moderately swollen and warm with signs of both intra-articular fluid and synovial hypertrophy. Flexion and extension were limited by 10 degrees. The child was afebrile and appeared otherwise healthy. There were no abnormal pulmonary signs and no peripheral lymphadenopathy. The remai