Results
76 patients were approached to participate in the study; 7 patients did not complete the study due to non-cooperation with the LUS examination (n=3) or poor LUS image quality (n=4). A total of 52 participants were included in the final analysis (Figure 1). Clinical characteristics of those who completed the study are presented in Table 1. The majority of patients were male (66%) with a median age of 11 years (IQR 8, 14). Thirty-three (63%) patients were diagnosed with asthma via positive MCT, and the remainder had a positive spirometry diagnoses. A large portion (42%) of patients had asthma that was categorized as severe following the ISAAC score, and 16% had poorly controlled asthma on ACQ questionnaires.
Ten of the 52 patients had a positive LUS (19.2%, [95CI 8.3%-30.1%]). Of the patients with a positive LUS, 8 had ≥3 B lines in an intercostal space, 7 had small subpleural consolidations (<1cm), 1 had a larger consolidation (>1cm) and 1 had a pleural line abnormality (Table 2), (Figure 2). All the findings were isolated within one to two intercostal spaces in all the participants. There was a predilection for abnormalities to be in the right side, primarily on the lateral and anterior LUS zones (6/10 positive LUS), (Figure 3).
For the 10 patients with a positive LUS, their median FEV1 score on the day of recruitment was 100% predicted, while 4 had severe asthma per the ISAAC definition. Univariate analysis was performed to look at LUS positivity and the relationship with various clinical asthma symptoms (Table 1), however there were no significant associations. LUS positivity did not show an association with asthma severity per the ISAAC criteria (p = 0.579) or poorly controlled asthma per ACT score (p = 0.557). Further analysis looking at patients with reported wheeze in the past week (4/10, p = 0. 478) or recent SABA use (8/10, p = 0.165) did not show an association with LUS either.
A subanalysis was carried out in participants who were already followed at the clinic for asthma control and those who had a positive MCT result on the day of the visit for asthma diagnosis. The results are shown in Table 3. There were no significant associations found in the subanalysis between having a positive LUS in each individual group and the different variables. This analysis was only exploratory as it was not powered appropriately. When comparing the two groups, there is a higher rate of positive LUS in the known asthma group compared to those who presented for a confirmatory MCT (6/19 vs 4/33). Analysis to look at different variables between the two groups found that there was a significant difference in the number of patients with lower FEV1 (p 0.012), FEV1/FVC (p<0.001) and the use of ICS/LABA (0.004) for maintenance therapy in the known asthmatic group compared to patients who presented for an MCT to diagnose asthma.
Using the LUS quantitative scoring system, (E-Appendix B), 9/10 of the patients had a score of 1, and only one patient had a score of 2 (patient with a >1cm consolidation).