Eosinophilic inflammation and muscle mass in chronic airway disease

Abstract

<b>Background:</b> Muscle wasting is related to poor prognosis in COPD with systemic inflammation considered as a main cause. In asthma, both high levels of eosinophilic inflammation and low muscle mass are observed in severe disease. Whether systemic eosinophilic inflammation is related to low muscle mass in patients with ‘chronic airway disease’ (CAD) is unknown. <b>Aims:</b> To compare muscle mass levels between adults with and without CAD. To assess the association of muscle mass and blood eosinophil levels in both groups. <b>Methods:</b> Using LifeLines Cohort data (n=152 728), CAD was defined as ≥2 of: self-reported asthma or COPD, FEV₁/FVC&lt;LNN or respiratory medication. Controls met none of the criteria. Muscle mass was assessed by creatinine excretion in 24h urine, and was associated with blood eosinophils in a linear regression model adjusted for sex, age, BMI, smoking and physical activity. <b>Results:</b> We identified 8228 adults with CAD (38% men, age 45±13) and 32 724 controls (30% men, age 45±13). Sex-specific adjusted mean creatinine excretion was lower in adults with CAD compared to controls (♂1869 ♀1245 vs ♂1883 ♀1259 mg/day, p&lt;0.001), whereas blood eosinophils were higher in CAD (♂0.25 ♀0.20 vs ♂0.19 ♀0.16 *10⁹/L, p&lt;0.001). Each 0.1*10⁹/L increase in blood eosinophils was associated with a 4.09 mg/day lower creatinine excretion (95%CI -8.18,-0.01) in adults with CAD. This was similar to controls (-4.73; 95%CI -7.27,-2.18; p_int= 0.66). <b>Conclusion:</b> Higher systemic eosinophilic inflammation was related to lower urinary creatinine excretion, indicating less muscle mass. Although not specific to CAD, this finding stimulates to explore the clinical relevance of low muscle mass and response to anti-inflammatory therapy in eosinophilic CAD.