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Rheumatoid arthritis (RA) is linked to almost a twofold increased risk for Parkinson’s disease (PD), new research shows.

Claims data in 55,000 patients with RA and 273,000 age- and sex-matched controls show that those with RA were 1.74 times more likely than controls to be diagnosed with PD.

Hyungjin Kim, nitrofurantoin 400mg MD, PhD

“If patients with rheumatoid arthritis begin exhibiting motor symptoms such as muscle rigidity, tremors, or slowed movement, it is imperative that they be evaluated by a qualified neurologist to rule out the possibility of developing Parkinson’s disease,” study investigator Hyungjin Kim, MD, PhD, told Medscape Medical News.

Kim is an associate professor in the department of medical humanities at Sungkyunkwan University School of Medicine in Seoul, Korea.

The findings were published online May 1 in JAMA Neurology.

Conflicting Findings

The investigators note that a number of studies have examined the link between RA and PD, with conflicting results — one even showing a 35% reduced risk for PD for individuals with RA. A more recent population-based study in Taiwan showed a 37% higher rate of PD in patients with rheumatic disease.

However, previous studies did not control for important variables such as body mass index or diabetes.

For the current study, the investigators analyzed claims on about 55,000 patients diagnosed with RA between 2010 and 2017, with follow-up until 2019, and compared the outcomes of this group vs those of 273,000 controls.

The mean age of claimants was 58 years, and 75% were female.

Results showed that those diagnosed with seropositive RA were about twice as likely as controls to be diagnosed with PD. Those with seronegative RA were 1.2 times as likely as controls to be diagnosed with PD.

Kim noted that although the pathogenic link between RA and PD remains elusive, inflammation probably plays an important role. “Inflammatory cytokines such as tumor necrosis factor alpha and interleukin-6, which are increased in RA patients, can induce microglial activation, leading to neuroinflammation,” he stated.

“These inflammatory cytokines are known to be associated with the dysfunction and degeneration of nigral dopaminergic neurons, which are important in the pathogenesis of PD,” he added.

The investigators noted that patients with RA may have been subject to more frequent healthcare services than controls and so were more likely to obtain a PD diagnosis.

Another possibility was that because patients with health check-ups were included in the analysis, the findings may have been biased toward those who were older and who had a higher income.

Kim noted that additional research is required to clarify the pathogenic connection between RA and PD.

“Moreover, additional studies are necessary to explore the potential influence of novel therapeutic treatments for RA on Parkinson’s disease susceptibility in patients with RA,” he said.

David Sulzer, PhD

Commenting on the findings for Medscape Medical News, David Sulzer, PhD, professor of psychiatry, neurology, and pharmacology at Columbia University in New York, said that the study adds to the growing body of evidence showing there is an autoimmune component to PD.

Sulzer pointed to data in several papers he published with others to this effect, including one showing higher rates of PD in people with inflammatory bowel disease.

The study had no specific funding. The study investigators and Sulzer report no relevant disclosures.

JAMA Neurol. Published online May 1, 2023. Abstract

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