Background/Purpose: Rheumatoid Arthritis (RA) is an autoimmune disease of systemic inflammation primarily involving the small synovial joints. Approximately 1.5 million adults in the United States have RA. Interstitial Lung Disease (ILD) is present in 35% of RA cases, and pulmonary complications are responsible for 10-20% of RA-related deaths. Currently, the burden of RA-ILD in the San Joaquin Valley is unknown. This study aims to enhance understanding of this unique condition and its representation in our community; consequently creating the framework for a database of RA-ILD patients.

Methods: In this retrospective, case-control study medical records from CRMC, ACC and URA during January 2013-May 2017 were reviewed to identify and analyze subjects with both RA and ILD. Statistical analysis using Pearsons Chi Square and Logistic Regression was employed to compare characteristics of subjects with RA-ILD (cases) to those with ILD alone (controls).

Results: 4767 subjects with ILD were identified. 34 of these were diagnosed with RA, giving RA a prevalence of 0.7% within the ILD population. 528 subjects with RA were identified. 34 of these were also diagnosed with ILD giving ILD a prevalence of 6.4% within the RA population. The majority of RA-ILD subjects were Hispanic males. 50% were smokers with an average of 37 pack years. The majority had been prescribed steroids, with an average maintenance dose of 6mg prednisone daily. All were prescribed a non-biologic DMARD, with hydroxychloroquine being the most common; while only 32% were prescribed a biologic DMARD. CCP and RF were tested in 93% of cases, and 75% were positive. There was a significant relation between RA-ILD and ILD alone with regards to CCP positivity [X²(2, N=44)=12.37, p=0.002], RF positivity [X²(2, N=46)=10.73, p=0.005], steroid use [X²(1, N=81)=11.15, p=0.01], biologic DMARD therapy [X²(1, N=81)=11.56, p=0.01], and non-biologic DMARD therapy (p<0.001). Subjects with a positive CCP were 52 times more likely to have RA-ILD than CCP negative subjects (OR 52.01; CI 1.83 – 1473.63; p=0.02). RF positivity was also strongly associated with RA-ILD (OR 16.68; CI 1.25 – 223.16; p=0.03). In both groups, restrictive pulmonary disease was most common. The average %DLCO of the RA-ILD group was 43% whereas that of the control group was 91%.

Conclusion:

This investigation elucidated significant clinical characteristics and treatment patterns among RA-ILD patients in the Central Valley. The high rate of CCP positivity in patients with RA-ILD may support that CCP is linked to aggressive RA with more frequent extra-articular manifestations. Further research is needed to investigate the risk of RA development in the ILD population with CCP positivity. Our RA-ILD population may have more severe pulmonary disease compared to ILD alone, reflected by a much lower average %DLCO. Future studies should examine the effects of anti-TNF therapy on pulmonary function in RA-ILD. Routine TB and cocci screening and pulmonary function testing in this population may be indicated as a result of this study. Standardized coding for RA-ILD may improve our ability to capture more patients and increase the sample size, which was a limiting factor in this study.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-prevalence-and-clinical-characteristics-of-rheumatoid-arthritis-with-interstitial-lung-disease-in-the-san-joaquin-valley-of-central-california/