NEW YORK (Reuters Health) – Rheumatoid arthritis patients with a high body mass index (BMI), the ratio of weight to height used to classify people into weight categories, have less joint destruction in the early stages of the disease than do their lower-BMI counterparts, according to a report from the Netherlands published in the Annals of the Rheumatic Diseases.

“This is an intriguing observation that needs to be thoroughly investigated,” Dr. Annette H. M. van der Helm-van Mil told Reuters Health. “It may reveal new biological mechanisms that have a protective influence on joint damage in rheumatoid arthritis.”

van der Helm-van Mil and colleagues from Leiden University Medical Center investigated whether obesity is a risk factor for the development of rheumatoid arthritis among 570 patients with undifferentiated arthritis, and whether the BMI of patients at the onset of rheumatoid arthritis correlates with the level of joint destruction during 3 years of follow-up.

BMI and obesity had no influence on the risk of progressing from unclassified arthritis to rheumatoid arthritis, the authors report.

In contrast, there was an inverse correlation between initial BMI and joint destruction, after 3 years of follow-up. BMI correlated inversely with total erosion scores and the total joint space narrowing scores.

“Our department of rheumatology will perform further studies on the effect of obesity on rheumatoid arthritis as well as osteoarthritis,” the age-related type of arthritis, van der Helm-van Mil added. This will involve studies of synovial tissue from overweight and normal-weight patients, blood studies and animal studies.

She hopes the study findings “subsequently can lead to the development of new targeted therapies.”

SOUCE: Annals of the Rheumatic Diseases, June 2008.