Researchers have found inflammation linked to the painful joint condition plays an important role in triggering Alzheimer's, the deadly brain disease.
The inflammation boosts production of toxic cells in the brain called plaques.
Now, experts believe drugs for arthritis could also be used to treat dementia, the Daily Express reported.
"With this link, we have a new path to potentially identifying and attacking this horrible disease," said leader of the research, Dr Douglas Golenbock from the University of Massachusetts Medical School.
One expert even said the evidence could lead to the "Holy Grail" in the study of the disease.
"As current treatments merely stabilise the condition, finding ways to stop the physical causes building up in the first place is the Holy Grail for researchers," Jess Smith, of the Alzheimer's Society, said.
"We've known for years that the plaques associated with Alzheimer's were surrounded by microglia, the resident immune cell of the central nervous system. What we didn't know was what role, if any, inflammation played in the progression of the disease," Golenbock said.
The study found that an immune process in the body sparks the production of a protein called interleukin-1 beta (IL-1B).
This protein is involved in the body's defence against infection and has also been pinpointed as a drug target for rheumatoid arthritis - which occurs when the immune system attacks joints, causing pain and inflammation.
The study, published in the journal Nature, points to the possibility that drugs that disrupt the production of IL-1B, such as those for rheumatoid arthritis, may also benefit Alzheimer's patients.
Previously, brain inflammation in Alzheimer's sufferers was thought to be a side effect. But increasing scientific evidence suggests that it might be a primary cause, raising the possibility of fighting Alzheimer's with common anti-inflammatories such as aspirin and ibuprofen.
"The findings are still at an early stage but research into inflammation in Alzheimer's is an important area for the future," Dr Simon Ridley, of Alzheimer's Research UK, said.