As you know, rheumatoid arthritis is a disease of the joints, but some people with RA say that it can also take a toll on a very important organ: the brain. They describe feeling forgetful, unable to concentrate and gripped by the “blahs.” In other words, they say that RA gives them an unshakable case of brain fog.

Brain fog isn’t a medical term, but doctors have long recognized that patients with certain physical conditions (such as lupus and multiple sclerosis) can experience cognitive dysfunction, or the diminished ability to think, learn, remember and perform other mental tasks. Not all doctors who treat RA are convinced that brain fog represents an important concern for their patients. Yet recent research offers clues that diseases featuring chronically elevated inflammation, such as RA, may hinder healthy brain performance.

“I see it all the time,” says Marian Rissenberg, PhD, a neuropsychologist who works with patients coping with cognitive problems at Northern Westchester Hospital in Mount Kisco, New York. “These people are not malingerers.”

Surprisingly Common

No one is sure how many people with RA experience brain fog, but a few researchers have tried to get a handle on the question by administering standardized cognitive tests to patients. A pair of small studies performed in 2002 and 2004 found that anywhere from 30 percent to 71 percent of RA patients performed poorly on various cognitive tests.

More recently, a team at the University of California at San Francisco conducted one of the largest investigations on the cognitive abilities of RA patients to date, which was published in Arthritis Care & Research in August 2012. Researcher So Young Shin and her colleagues gave a wide-ranging battery of cognitive tests to 115 RA patients. Shin’s group found that many of the study participants struggled with mental clarity and sharpness: 31 percent scored poorly on four or more of 16 different measurements of cognitive ability.

Who Gets Brain Fog — and Why?

What is it about RA that might cloud the mind and dulls the wits? “At this point, we can only assume that several mechanisms… may affect cognitive impairment in RA,” says Shin via e-mail. Shin’s study found that patients who used corticosteroid drugs — a common treatment for RA — and who had risk factors for heart disease (such as high blood pressure and high cholesterol) were most likely to have cognitive dysfunction. She notes that past studies have these medications and heart risk factors to fuzzy thinking, too, though no one is sure why.

What’s more, some studies suggest that the depression and anxiety that can accompany coping with chronic pain may impair cognition. A 2010 experiment at the University of Windsor in Ontario, Canada, found that RA patients with high levels of pain did poorly on tests of so-called executive functions, which include planning, decision-making, and working memory (which helps you to follow instructions, among other roles).