First Asian case of biopsy-confirmed manubriosternal joint involvement in rheumatoid arthritis

Rheumatoid arthritis (RA) is an inflammatory polyarthritis that typically affects the small joints but can also involve the manubriosternal joint (MSJ). Although cases of MSJ involvement in RA are rare, such cases present with chest pain, a mass-like lesion, and subluxation. These cases can also be diagnosed incidentally, while patients are asymptomatic. It is important to differentiate RA involving the MSJ from other diseases such as ankylosing spondylitis that can affect the MSJ. Several cases of RA affecting the MSJ have been reported in Western countries, but none have been reported to date in Asia, especially with disease activity of RA. Here, we report a case of RA in the MSJ that was confirmed by imaging and histological investigation in a middle-aged Asian woman.