To the Editor—Chan et al1 drew our attention to the fact that tuberculosis can be a great mimicker of other conditions when it affects the knee. Conversely the knee may be a site where problems may mimic other disorders. Knee injuries are among the most common disabling conditions that arise from sporting and other accidents or falls. The presence of septic arthritis may overlap or complicate a traumatic knee condition. Septic arthritis by itself may affect the knee, as well as autoimmune-related arthritis. Yet uncommonly, gout and other crystal arthritis may have a similar clinical and radiological presentation.2 Only when urate or calcium pyrophosphate are identified can the diagnosis be confirmed. The title ‘great mimicker’ was originally applied to syphilis, a disease that declined considerably in the last century but that is recently exhibiting a resurgence due to uncontrolled sexually transmitted diseases.3 Syphilis targets virtually every organ and the knee is no exception. In North America, another spirochete infection, Lyme disease, is known to infect people bitten by ticks or in contact with wild animals, and prominent among its symptoms is arthritis, including that of the knee.4 In Hong Kong, we do not have Lyme disease but we should maintain a high index of suspicion in individuals who have visited North America and who present with fever, fatigue and joint pain. The risk is not confined to recent exposures since the disease may be quiescent for months or even years before a flare-up.

The author solely contributed to the concept or design, acquisition of data, analysis or interpretation of data, drafting of the letter, and critical revision of the letter for important intellectual content. The author had full access to the data, contributed to the study, approved the final version for publication, and takes responsibility for its accuracy and integrity.

The author has disclosed no conflict of interest.

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1. Chan HM, Fu H, Chiu KY. Tuberculosis of the knee as a great mimicker of inflammatory arthritis: a case report. Hong Kong Med J 2023;29:548-50. Crossref

2. Yun SY, Choo HJ, Jeong HW, Lee SJ. Comparison of MR findings between patients with septic arthritis and acute gouty arthritis of the knee. J Korean Soc Radiol 2022;83:1071-80. Crossref

3. Peeling RW, Hook EW 3rd. The pathogenesis of syphilis: the great mimicker, revisited. J Pathol 2006;208:224-32. Crossref

4. Arvikar SL, Steere AC. Diagnosis and treatment of Lyme arthritis. Infect Dis Clin North Am 2015;29:269-80. Crossref