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We all know that the microbiome in the gut may be very important for multiple immune diseases. However, new findings from the ACR, 2019 in Atlanta reinforce how important the interface is between the lungs and developing rheumatoid arthritis.
It has been known that cyclical citrullinated proteins that are immunogenic (causing ACPAs) may develop in the lungs before RA. We also know that restrictive lung disease (interstitial lung disease, ILD) is increased in RA. Two studies showed that before the onset of RA, obstructive lung disease - COPD and, less so, asthma new onset - increased.
The Nurses Health Study demonstrated that new RA onset onset had increased COPD as a new diagnosis first with almost a two-fold risk with matching people without developing RA and adjusting for smoking. The risk was higher in seropositive patients compared to seronegative. The onset of asthma was also increased but with less frequency than new onset COPD which makes sense due to the age of the cohort that was followed (1). Another study of patients at risk for RA (pre-RA, +ACPA) had an increased risk of obstructive lung disease (COPD and asthma) especially in the pre-RA period; more than after RA was diagnosed (3). A final tidbit, in areas of high air pollution, there was an increase in ACPA positivity (3). This doesn’t mean a cause and effect but interesting as air pollution of course can inflame lungs.
What does this mean clinically? We need to be aware that in RA there is not only an increase in ILD, but also COPD which may certainly predate RA. Inflammation of the lungs causes protiens to citrullinate (likely) and increases antibody production. Of course, smoking is more common in RA but other studies have adjusted for presumed smoking rates and still saw more hospitalizations for COPD prior to RA onset.
- Ford J, et al. ACR 2019, Atlanta, #186
- Zaccardelli A, et al. ACR 2019, Atlanta, #841
- Zhao N, et al. ACR 2019, Atlanta, #L02
- Mcguire K,et al. Arthritis Care Res. 2019;71:602-610. doi: 10.1002/acr.23410