Tuberculous arthritis of the ankle joint masquerading as rheumatoid arthritis in a patient with lupus nephritis.

Tuberculosis is an airborne multisystemic disease which primarily infects the lungs. Isolated tuberculous arthritis is rare. We present a case of a 41-year-old woman with a known case of lupus nephritis class IV who complained of pain and swelling over her left ankle joint for several months. She was treated for rheumatoid arthritis and was started with immunosuppressive agents. However, she did not improve with treatment and was later diagnosed with tuberculous arthritis based on a molecular study from joint aspiration. She was started on antituberculosis medication and showed improvement. We highlight the challenges in reaching the diagnosis and the importance of including tuberculous arthritis in differential diagnoses in cases with persistent ankle swelling. © Royal College of Physicians 2021. All rights reserved.