Clinical and pulmonary function changes in cough variant asthma with small airway disease

It is known that small airway disease is present across all asthma severities; however, its prevalence and clinical characteristics in cough variant asthma (CVA) have not been fully illuminated.

A total of 77 CVA patients with preserved proximal airway function (FEV1/FVC > 70%) were enrolled in this study. The correlation between forced expiratory flow at 50% (FEF_50%) and FEF_25-75% in the CVA population was first evaluated. FEF_50% was determined to be an easy and feasible parameter for identifying small airway disease. CVA with small airway disease is defined as FEF_50% < 70%, whereas CVA with normal small airways is identified as FEF_50% > 70%. Demographic features, clinical characteristics, lung function and induced sputum test results were determined at the initial visit and at the final visit 1 year later.

FEF_50% is a good marker for small airway disease. The cutoff value of 70% is more sensitive than the previously published 60% for identifying more patients with small airway problems early. Nearly half of the CVA population (45.4%) in our cohort had small airway disease. In both group, symptoms improved greatly after anti-asthmatic treatment. Interestingly, the changes in symptom scores [Asthma Control Test (ACT) and ACQ] were even greater in the CVA with small airway disease group than in the control group because of the higher medication usage in this subpopulation in real life. However anti-asthmatic therapy can not reverse small airway dysfunction. At last visit, FEF_50% of CVA with small airway diseases was 57.2% ± 10.5%, still much lower than the control group (FEF_50% = 92.6% ± 16.5%).

In our cohort, nearly half of the CVA population had small airway disease. Their demographic features, clinical characteristics, airway eosinophils and drug responsiveness were quite similar between two groups, which means these indices can not be used as markers to identify small airway obstruction. We found FEF_50% is an easy and feasible marker for early identification. Regular anti-asthmatic medication helped to improve clinical scores in patients with small airway disease, but the obstruction could not be reversed over 1-year period.