Introduction Children with severe therapy resistant asthma (STRA) have heterogeneous disease with variable response to steroids. Currently, spirometry (forced expiratory volume in 1 s (FEV1)) is most widely used to assess treatment response. We hypothesised lung clearance index (LCI) would more sensitively assess steroid response than FEV1 alone, using our multi-domain approach [JACI 2016;138:413–420] with the addition of LCI to measure response of distal airway disease.

Methods 39 children with STRA were recruited during a clinically-indicated admission for bronchoscopy and intramuscular triamcinolone injection. Prior to triamcinolone, they performed LCI, spirometry, FeNO, and filled in the asthma control test (ACT). They were followed up at 4 weeks and these tests repeated. ACT was considered abnormal if <20, LCI if ≥7.1, FEV1 percent predicted below 80%, and FeNO if ≥24 parts per billion. Any domain which was abnormal at visit 2 was a non-response.

Results 26/39 (67%) patients had at least a partial response, see Table. There was strongest concordance of Results between FeNO and LCI (70%). 11/39 (28%) of patients had a response in at least two domains, 4/39 (10%) at least three, and 1 patient responded in all four domains.

Conclusions In this cohort, LCI, FeNO and FEV1 were equally likely to be abnormal at baseline. FeNO and LCI were most likely to respond, (36% and 33% respectively), whereas FEV1 was least responsive to systemic steroids. Using this multi-domain approach 67% improved over 4 weeks following treatment with systemic corticosteroid. The clinical significance of an LCI response remains to be determined. We speculate that this group may reflect a distal airway disease phenotype who may benefit from fine particle inhaled corticosteroids.