Farah CS, et al. - In a prospective cohort of 20 adults (12 male) with severe eosinophilic asthma (SEA) commencing monthly mepolizumab, researchers assessed changes in ventilation inhomogeneity, a marker of small airway function, post-commencement of mepolizumab. They determined global (Lung Clearance Index, [LCI]) and regional ventilation inhomogeneity in acinar (Sacin) and conducting (Scond) airways, at baseline, Week 4 and Week 26, by using the Asthma Control Questionnaire (ACQ-5), spirometry, fraction of exhaled nitric oxide (FeNO) and multiple breath nitrogen washout. They used RM-ANOVA and paired t-tests to evaluate treatment related changes. Marked improvements on ACQ-5, spirometry, LCI and Sacin were seen at Week 4, which sustained at Week 26. There was a correlation between change in ACQ-5 and change in Sacin and FRC, but not with spirometry changes. Overall, mepolizumab commencement resulted in rapidly improved symptom control. An association was observed between early improvement in small airway function and asthma control. The early improvement in small airway function could be a significant contributor to the therapeutic response.