Prevalence of low body mass in rheumatoid arthritis: association with the acute phase response.

OBJECTIVE To ascertain the prevalence of low body mass in a rheumatoid arthritis (RA) population and to explore a possible relation with the acute phase response. METHODS 97 patients who fulfilled the American College of Rheumatology (ACR) criteria for RA were recruited. Change in weight from initial presentation was noted. Body mass index (BMI), upper arm fat and muscle areas were recorded together with fat free mass calculated from the waist measurement. Blood samples were taken for erythrocyte sedimentation rate (ESR), C reactive protein (CRP), and serum albumin. RESULTS 13% of the RA group fell into the lowest 5th centile for BMI for the general population. The loss of body mass was greater for lean tissue than fat, with over 50% of the RA group falling into the lowest 10th centile of a reference population for the upper arm muscle area. Female patients who lost greater than 15% of their initial weight had higher health assessment questionnaire (HAQ) results than the rest of the group (p = 0.020). In female patients there was a significant correlation between reduced fat free mass and the acute phase response (ESR p = 0.016 and CRP p = 0.003) CONCLUSIONS There is an increased prevalence of low body mass, greatest for lean tissue, in the RA population. In the female group there was an inverse relation between the acute phase response and fat free mass. Female patients with RA who lose a significant amount of weight are more disabled as assessed by HAQ.