A 65-year-old female was diagnosed with rheumatoid arthritis about 10 years. She had experienced continous severe knee pain from the last six months in her right knee. She had undergone treatment with methotrexate (MTX) 6–8 mg/week as the sole regimen over the last eight years. At this time, the patient was walking with the aid of crutches, and her Knee Society Knee Score and Functional Score [1] were 47 points and 5 points, respectively. Severe joint space narrowing was evident on upright anteroposterior radiography (Figure 1A), which is an indication for total knee arthroplasty. Due to persistent disease activity (DAS28 = 4.1), the patient was started on MTX 8 mg/week plus intravenous abatacept 500 mg/month. After 18 months of this treatment, there was improvement of symptoms, mostly in the right knee. The patient’s Knee Society Knee Score and Functional Score had increased to 80 points and 60 points, respectively. She was able to walk independently without crutches, and upright anteroposterior radiography showed widening of the narrow knee joint space (Figure 1B).

To date, abatacept has been known as an agent that reduces the progression of radiographic structural damage in rheumatoid arthritis patients with an inadequate response to MTX [2][3][4] . However, this case showed widening of the narrow knee joint space after the introduction of abatacept treatment. We believe that our case is the first to demonstrate this knee joint space widening, which is expected to be extended with longer-term observations of this rheumatoid knee. As both the Knee Society Knee Score and Functional Score were also improved, it is likely that the impaired cartilage tissue within the right knee joint was being substituted by cartilage-like tissue through some as yet unclarified mechanisms. This change likely occurred because combined methotrexate and abatacept therapy has a strong effect on the chemical environment and cartilage regeneration within the rheumatoid knee joint.

This case showed widening of the narrow rheumatoid knee joint space associated with combination therapy with methotrexate plus abatacept. In addition, both the Knee Society Knee Score and functional score were also improved after the introduction of this combination therapy. Additional work is required for understanding the rheumatology underlying this case.

1. Insall JN, Dorr LD, Scott RD, Scott WN. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989 Nov;(248):13–4.   [CrossRef]   [Pubmed]    
2. Kremer JM, Genant HK, Moreland LW, et al. Effects of abatacept in patients with methotrexate-resistant active rheumatoid arthritis: A randomized trial. Ann Intern Med 2006 Jun 20;144(12):865–76.   [CrossRef]   [Pubmed]    
3. Genant HK, Peterfy CG, Westhovens R, et al. Abatacept inhibits progression of structural damage in rheumatoid arthritis: Results from the long-term extension of the AIM trial. Ann Rheum Dis 2008 Aug;67(8):1084–9.   [CrossRef]   [Pubmed]    
4. Kremer JM, Peterfy C, Russell AS, et al. Longterm safety, efficacy, and inhibition of structural damage progression over 5 years of treatment with abatacept in patients with rheumatoid arthritis in the abatacept in inadequate responders to methotrexate trial. J Rheumatol 2014 Jun;41(6):1077–87.   [CrossRef]   [Pubmed]