Main idea: A Rheumatoid arthritis diagnosis is significantly associated with a lower incidence of subsequent PD diagnosis. We propose that common anti-inflammatory treatments used in RA might protect against the later development of PD . This hypothesis can be tested by examining PD risk imposed by the use of anti-inflammatory drugs in conditions other than RA. These data should be taken into account when developing- and clinically evaluating new or repurposed drugs aimed at modifying the disease process in PD.
Rheumatoid arthritis (RA) and the genetic risk landscape of autoimmune disorders and Parkinson’s disease overlap. Anti-inflammatory medications used to treat RA might influence PD risk. The aim is to use a population-based approach to determine if there is an association between pre-occurring rheumatoid arthritis (RA) and later-life risk of Parkinson’s disease (PD). The study population was 3.6 million residents of Sweden, who were alive during part or all of the follow-up period; 1997-2016. We identified 30,032 PD patients, 8,256 of whom each was matched to ten controls. We determined the risk reduction for PD in individuals previously diagnosed with RA. We also determined if the time (in relation to the index year) of the RA diagnosis influenced PD risk and repeated the analysis in a sex-stratified setting. Individuals with a previous diagnosis of RA had a decreased risk of later developing PD by 30-50% compared to individuals without an RA diagnosis. This relationship was strongest in our conservative analysis, where the first PD diagnosis occurred close to the earliest PD symptoms, with the greatest risk reduction in females. Our findings provide evidence that individuals diagnosed with RA have a significantly lower risk of developing PD than the general population. Our data should be considered when developing or repurposing therapies aimed at modifying the course of PD.