The time of year when rheumatoid arthritis (RA) symptoms first appear may predict their severity. That’s the finding of a new study presented at the annual European Congress of Rheumatology Conference, or EULAR, in Copenhagen, Denmark this month.

Scientists studied X-rays of the hands, wrists and feet of 736 French patients, who had inflammation of at least two joints for six weeks to six months. What they found was that those who developed rheumatoid arthritis in the winter or spring had more severe symptoms six months later than those who developed the condition in the summer or fall.

Gaël Mouterde, MD, with the Immuno-Rheumatology Department at Lapeyronie Hospital in Montpellier, France, led the research and says this study shows a distinct relationship between rheumatoid arthritis progression and seasonal onset.

“It is just an interesting finding that can help to understand rheumatoid arthritis physiopathology,” Mouterde says.

At this point, scientists can only hypothesize why this is happening.  “We postulate that this could be as a result of either a vitamin D deficiency, or environmental factors, such as winter virus,” Mouterde says.

Winter viruses can influence protein citrullination and anti-citrullinated protein antibodies or ACPAs, which attack one or more of the body’s own tissues, are often found in the immune systems of rheumatoid arthritis patients.

“If it is confirmed in other cohorts, particularly northern cohorts, where sun is rare, and where vitamin D deficiency is more frequent, and if we identify the explanation, we could try to treat patients with vitamin D for example, before the symptoms worsen,” Dr. Mouterde says.

No differences were visible in study participants a full year later. Researchers think that’s because these initial environmental factors have less of an effect over the long term.

Paul Howard, MD is the director of Arthritis Health, an integrated medical practice for patients with arthritis and autoimmune disorders in Scottsdale, Ariz. He says the results of the study are surprising and very interesting.

“I’ve never seen anything like it before in terms of associating the time of onset of disease and the severity of arthritis,” Dr. Howard says.  “I think it’s a unique observation. This is not something that most studies have gone back and asked – 'When did your symptoms start? What season?' So it’s not something that’s been asked a lot.”

Dr. Howard says this information might help identify patients who won’t do as well, but for doctors treating rheumatoid arthritis patients, it doesn’t change much. “It wouldn’t change how I treat people. It’s interesting and it might lend itself to more investigating as to why some people progress more rapidly with more damage and disease,” Howard says. “But I’m going to treat people aggressively whether they got [RA] in the summer or winter.”

Mouterde says researchers hope this discovery can help identify rheumatoid arthritis patients at a higher risk of developing structural damage who could be helped with early and intensive therapy.