Does reduced muscle density contribute to physical dysfunction in rheumatoid arthritis?

This study investigated the effects of low muscle density on physical strength and function in patients with rheumatoid arthritis. The study concluded that low muscle density was associated with greater disease activity, reduced muscle strength and poorer physical function.

Rheumatoid arthritis (RA) is a chronic condition that causes painful swelling and inflammation in the joints. It is an autoimmune condition – this occurs when the body’s immune system starts to attack healthy tissue.

Low muscle density in patients with RA is associated with greater disease activity. This can cause poor physical function. Some studies suggest that the loss in muscle is replaced by fat. It is unclear if an increase in intramuscular fat and/or a loss of muscle density causes reduced physical function. 

This study investigated the effects of body composition (fat versus muscle) on disease activity and physical function in patients with RA.

This study included 103 patients with RA and 428 healthy controls. A number of analyses were performed to assess body composition, disease state and physical function. Body composition was assessed by measuring muscle density and fat composition. Disease state was measured using a number of clinical parameters including DAS28 (disease activity score 28), c-reactive protein (CRP) and markers of inflammation. Physical function and disability was assessed using physical activity scores (PAS), th Short Physical Performance Battery (SPPB), health assessment questionnaires (HAQ) and clinical measures of muscle strength.

Patients with lower muscle density had higher levels of disease activity, indicated by increased inflammation and long-term use of prednisone (a steroid).  Patients with lower muscle density were also more likely to smoke and have sedentary lifestyles. Low muscle density was associated with reduced muscle strength and physical function. Low muscle mass and excess fat was not strongly associated to physical dysfunction. Muscle density and strength were more closely associated in patients with RA compared to healthy controls.

This study concluded that with low muscle density had greater disease activity, reduced muscle strength and poorer physical function.

This study is observational. It cannot determine if reduced muscle density actually causes poorer physical function in RA. Long-term studies monitoring body composition are needed to understand this further. 

If you have any concerns regarding physical function and RA treatment, please discuss with your physician.