The sternoclavicular joint is a diarthrodial joint that can be involved in rheumatoid arthritis (RA), and is detectable by ultrasound (US) examination in 15% of patients with RA1. Methotrexate-related lymphoproliferative disorder (MTX-LPD) occurs in extranodal sites in about 40%–50% of the affected patients2; however, intraarticular MTX-LPD is a very rare manifestation with only 1 case report occurring in the knee joint3.
A 67-year-old Japanese woman with a 40-year history of RA, treated with MTX (6 mg/week) for 15 years, presented to our hospital complaining of right sternoclavicular joint swelling (Figure 1A). The serum levels of C-reactive protein (5.68 mg/dl, normal < 0.3), lactate dehydrogenase (325 IU/l, normal 125–237), and soluble interleukin 2 receptor (1340 U/ml, normal 145–519) were elevated. US examination of the swelling joint showed low echoic lesion accompanied with positive power Doppler. Sternoclavicular joint synovitis was suspected, and MTX was increased to 8 mg/week, resulting in the worsening of this joint lesion (Figure 1B). Skin biopsy of the ulcerated lesion revealed CD20+ atypical lymphocytes with Epstein-Barr virus (EBV) latent membrane protein 1 and EBV-encoded RNA-1 (Figure 2). The diagnosis of MTX-LPD associated with EBV was made. The sternoclavicular joint swelling disappeared 6 months after MTX discontinuation (Figure 1C).
This sternoclavicular joint swelling is suggested to be caused by MTX-LPD in the skin overlapping a joint. Mucocutaneous ulcer associated with EBV-positive LPD can develop during immunosuppressive therapy, including MTX4. MTX-LPD should be considered as the differential diagnosis of atypical joint swelling during the course of RA, and histopathologic examination should be carried out.
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