Can Obesity Impact Joint Swelling in RA?

In rheumatoid arthritis (RA), a high body mass index (BMI) could influence an individual’s risk of swelling of the lower-extremity joints, according to study findings.

Measuring disease activity in a patient with obesity can be challenging, according to lead study author Veena K. Ranganath, MD, MS, RhMSUS.

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“The obese RA patient is difficult to assess for swollen joints at times,” Ranganath, who is an associate professor of medicine in the Division of Rheumatology at the University of California, Los Angeles, told Rheumatology Consultant. “Obese patients are also known to have fibromyalgia and osteoarthritis, which can make it hard to know if the RA is more active or if the other comorbid conditions are.”

To determine the association between BMI and joints in RA, Ranganath and colleagues analyzed data on 323 participants with early seropositive RA and a swollen joint count equal to or more than 6/44, and a tender joint count equal to or more than 9/44.

Multiple participant variables were evaluated including the American College of Rheumatology (ACR) core set measures, Disease Activity Score (DAS), Clinical Disease Activity Index, and BMI.

“We had a unique opportunity to evaluate a cohort of patients where joint counts were not limited to the 28-joint count, but more comprehensive to include 44 where the ankles and feet were assessed,” Ranganath said.

Overall, DAS items, Health Assessment Questionnaire Disability Index, physician global, and a swollen joint count of 44 differed across all BMI groups.

Of the swollen joint count of 44, metacarpophalangeal joints and lower-extremity joints were associated with increased swelling across all BMI groups. After adjusting for ACR core set measures, the researchers found that obesity was significantly associated with lower-extremity swollen joint count.

The DAS 28 and Clinical Disease Activity Index, which emphasize upper-extremity joint assessment, were not significantly influenced by obesity.

“Examining the feet and ankles is important in RA. However, it is still unclear if the increase in swollen joints of the lower extremity is due to RA disease activity in the obese RA patients, or if this is due to dependent edema or osteoarthritis,” Ranganath said. “Further studies are needed; imaging in these cases with ultrasound or MRI may be of utility.”

—Colleen Murphy

Reference:

Ranganath VK, Duffy EL, Garg VK, et al. Obesity impacts swelling of ankle and foot joints in early rheumatoid arthritis patients. J Clin Rheumatol. 2019;25(3):e8-e11. doi:10.1097/RHU.0000000000000799.