Cachexia in rheumatoid arthritis is associated with inflammatory activity, physical disability, and low bioavailable insulin‐like growth factor

Abstract

Objectives: To examine the impact of inflammation, insulin‐like growth factor (IGF‐1) and its regulating binding protein (IGFBP‐1) on lean body mass (LBM) in patients with rheumatoid arthritis (RA).

Methods: In 60 inpatients (50 women), inflammatory activity was measured by Disease Activity Score 28 (DAS28), C‐reactive protein (CRP), and interleukin (IL)‐6, and physical disability by the Health Assessment Questionnaire (HAQ). LBM was assessed by dual‐energy X‐ray absorptiometry (DXA) and fat free mass index (FFMI; kg/m²) and fat mass index (FMI; kg/m²) were calculated.

Results: Median age was 65 years and disease duration 13 years. Fifty per cent of the patients had FFMI below the 10th percentile of a reference population and 45% had FMI above the 90th percentile, corresponding to the condition known as rheumatoid cachexia (loss of muscle mass in the presence of stable or increased FM). DAS28, CRP, and IL‐6 correlated negatively with LBM (p = 0.001, 0.001, and 0.018, respectively), as did HAQ (p = 0.001). Mean (confidence interval) IGF‐1 was in the normal range, at 130 (116–143) μg/L. IGFBP‐1 levels were elevated in patients (median 58 µg/L in women and 59 µg/L in men) compared with a normal population (33 µg/L in women and 24 µg/L in men). The ratio IGF‐1/IGFBP‐1, which reflects bioavailable IGF‐1, was low (2.0 µg/L) and was positively correlated with LBM (p = 0.015). In multiple regression analysis, 42% of the LBM variance was explained by IGF‐1/IGFBP‐1, HAQ score, and DAS28.

Conclusion: A large proportion of RA inpatients, mainly women, had rheumatoid cachexia. The muscle wasting was explained by inflammatory activity and physical disability as well as low bioavailable IGF‐1.