Septic arthritis due to non-tuberculous mycobacterium without effusion

Septic arthritis is an important but difficult to make diagnosis that leads to significant morbidity and mortality. Joint effusion is generally accepted to be a highly sensitive finding in septic arthritis; however, final diagnosis requires synovial fluid studies. Without a significant joint effusion, it is difficult to obtain synovial fluid. In this case report, we describe the presentation and diagnosis of septic arthritis in the first MTP due to mycobacterium chelonae in a 69 year old man with a history of gout and immunosuppression due to a heart transplant. There was notably no significant effusion in the joint on clinical examination or bedside ultrasound. As the patient was immunosuppressed, arthrocentesis was performed under ultrasound guidance. A needle was clearly visualized in the joint; however, minimal synovial fluid was obtained. The fluid grew Mycobacterium chelonae in culture. Subsequent joint washout revealed purulent synovial fluid that grew out the same bacteria. This case emphasizes the importance of obtaining synovial fluid to evaluate for septic arthritis, even when joint effusion is absent. Ultrasound guidance can facilitate this.