Airwave oscillometry (AO) can detect small airway dysfunction and measure treatment response to inhaled corticosteroids and bronchodilators.1 We compared spirometry and AO changes in severe eosinophilic asthma (SEA) patients treated with mepolizumab to identify the preferred method for assessing mepolizumab efficacy.
SEA patients from two UK specialist asthma centres, due to start mepolizumab at clinic, were recruited prior to receiving the first treatment dose. Spirometry (Vitalograph alpha, Vitalograph Ltd., Buckingham, UK), AO (Tremoflo, Thorasys, Montreal), exhaled nitric oxide (FeNO), blood eosinophils, induced sputum eosinophils, symptom and quality of life questionnaire scores were measured before and after ≥12 weeks of mepolizumab.
Thirteen patients completed assessments at both timepoints, of which 54% were female, 92% were Caucasian and mean (SD) age at study entry was 53 (15). 23% of patients were ex-smokers and none were current smokers.
At baseline, mean (SD) R5-20 was 0.31 (0.44) cmH2O.s/L, AX was 9.83 (9.62) cmH2O/L and X5 was -0.15 (1.12) cmH2O.s/L. Mean FEV1% predicted was 74%, FEV1/FVC was 69% and FEF25–75% predicted was 51%.
After 12 weeks, mean FEV1 and% predicted improved by 230 ml (p<0.01) and 9.4% (p<0.01), respectively. FEF25–75% predicted increased by 10.2% (p<0.05). There were no significant changes in FeNO or AO parameters. ACQ-5 score improved by 1.23 (MCID 0.5, p=0.02) and SGRQ improved by 16 points (MCID 4.0, p<0.01).
Change in ACQ-5 score correlated with FEV1 (r=-0.57, p=0.04), but not with change in R5-20 (r=-0.09, p=0.78). Change in sputum eosinophils was significantly associated with change in FEV1 (r=-0.94, p<0.001), but not AO indices. A relationship between changes in R5-20 and FEV1 or FEF25–75 was not observed.
Spirometry detected improvements in lung function after 12 weeks of mepolizumab in the absence of airwave oscillometry changes. There was a strong association between change in FEV1 and sputum eosinophil response to mepolizumab.