Background/Purpose:

The utility of synovial biopsy has been confirmed as an important research tool in increasing our understanding of the pathogenesis of RA, evaluating new treatments and identifying potential therapeutic targets.[1, 2]  However, no scoring system for the assessment of synovitis at knee arthroscopy has been validated against the histological grade of inflammation observed in the synovial biopsies retrieved.

Furthermore, the power that arthroscopy may have in identifying patients with active inflammation despite normal CRPs has not been reported. Finally, we currently understand only 32% of the variance in factors that predict joint destruction,[3] and macroscopic findings at arthroscopy may present an additional opportunity in assessing those most at risk of this disease course.

Aims

To validate synovitis scores at arthroscopy with histology scores, CRP levels and erosive disease on radiographs.

Methods:

141 patients with RA were recruited to undergo arthroscopy, and serum CRP levels were measured at the same time. The most recent set of hands and feet radiographs were assessed for the presence or absence of erosions. A macroscopic score of synovitis, graded at 5 unit intervals between 0-100, was recorded by the operator at each arthroscopy.

Synovitis scores were analysed using Pearson’s test for correlation, with categorical data for histology findings (no inflammation, mild inflammation, and moderate-severe inflammation).The same test was used to determine if there was a correlation between synovitis scores and CRP levels.

The Chi-square test was employed to test for a relationship between categorical synovitis scores (4 quartiles), and the presence or absence of erosions.

Results:

A correlation was observed between synovitis scores and histology findings (p=0.0014, r=0.2943).

There was no correlation with synovitis scores and CRP levels. 49 (34.8%) patients had normal CRP levels (0-5mg/l), with 29 (59.2%) having synovitis scores >50%.

An association was also observed with higher synovitis scores and the presence of erosions (p=0.0173).

Conclusion:

Synovitis can be reliably assessed by scores at arthroscopy, which correlate with subsequent histological findings. Arthroscopy has the power to identify patients with synovitis, where CRP levels are normal, favouring the concept that not all RA phenotypes manifest elevated CRP levels during active disease. Furthermore, those with high synovitis scores are more likely to have erosions on  radiographs.

1.            Gerlag DM, Tak PP. Novel approaches for the treatment of rheumatoid arthritis: Lessons from the evaluation of synovial biomarkers in clinical trials. Best Practice & Research Clinical Rheumatology 22(2), 311-323 (2008).

2.            Kraan MC, et al. Modulation of inflammation and metalloproteinase expression in synovial tissue by leflunomide and methotrexate in patients with active rheumatoid arthritis: Findings in a prospective, randomized, double‐blind, parallel‐design clinical trial in thirty‐nine patients at two centers. Arthritis & Rheumatism 43(8), 1820-1830 (2000).

3.            De Rooy DP, et al. Predicting arthritis outcomes–what can be learned from the leiden early arthritis clinic? Rheumatology (Oxford, England) 50(1), 93-100 (2011).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/validating-arthroscopic-findings-using-histology-status-for-erosive-disease-and-crp-in-ra/