Discussion
This is the first study characterizing LUS findings of pediatric asthma
patients at their baseline state of health. Our study showed that almost
20% of children diagnosed with asthma had positive LUS findings when
well. The most frequent findings seen were small consolidations and
localized B-lines. These findings may be present at baseline and are not
to be attributed to, for example, a co-existing pneumonia or viral upper
respiratory tract infection.
An important question to address is how our described findings may
impact the evaluation of an asthmatic patient with LUS. The findings we
have identified (mostly localized B-Lines in one intercostal space and
small consolidations less than 1cm) are similar to what was described in
previous studies, commonly seen in patients with mild bronchiolitis,
atelectasis and viral pneumonia12,18,30. Therefore,
using LUS to try and differentiate these conditions from baseline asthma
findings is not possible.
The findings on LUS in our cohort of patients were objectively small and
often localized to one lung zone, effecting no more than 2 rib spaces.
LUS scores were also quite low (signifying mild changes) in most of the
positive LUS cases. Thus, more severe LUS findings including
consolidations >1cm and B-lines involving more than 2
intercostal spaces or effecting more than one lung zone, are atypical
for a pediatric asthmatic patient at baseline and should be considered
clinically significant, alerting the clinician to other possible lung
parenchyma changes outside of what is typically seen in pediatric
asthmatic patients.
Positive LUS findings in this study were more frequently observed on the
right anterior and lateral lung zones.(Figure 3). These findings may
correspond to the right middle lobe, where atelectasis is commonly seen
in asthmatic patients31. We hypothesizese that these
LUS findings are from sub-segmental mucus plugging and atelectasis with
the known hypersecretory issues in asthma30,32-34
As a secondary objective, we explored the association of having severe
or poorly controlled asthma with a positive LUS. The majority of our
population had relatively mild asthma with a median of 96%, and only
17% had an ACQ score that is considered elevated. There was no
significant association between having positive LUS and poor asthma
control, high ISAAC score, or FEV1 value. However, there was a trend
toward more frequent LUS abnormalities in patients already followed in
the respiratory clinic for asthma. These previously known asthmatics had
significantly lower spirometry FEV1% predicted and were more likely to
be on maintenance therapy which included inhaled corticosteroid combined
and long-acting beta agonist than those who presented to the clinic for
asthma diagnosis with MCT (Table 3). Our LUS correlations with asthma
control or severity are only exploratory and further research should be
done explore these possible associations.
There are some limitations to this study. First, the sample size was
relatively small (yet adequately powered), and our recruited asthmatics
had overall mild disease. A larger and more severe asthma population may
detect significant relationships between different clinical variables
and likelihood of having a positive LUS. Second, sonographers attempted
to perform LUS before spirometry maneuvers, but some known asthmatics
had their scans completed after spirometry testing, which routinely
included the administration of Ventolin. This was not the case for any
of the MCT patients, as the scans were always done before the test. Both
spirometry maneuvers and beta agonists may have altered findings on LUS.
Three different sonographers performed the LUS evaluations, and
ultrasound images can often be influenced by operator specific
practices. However, the blinded interpretation by a single expert makes
this operator bias less of an issue, and prior studies show good
interrater reliability between sonographers and
interpreters19,20. Four the ISAAC score was used in
our study as a surrogate measure to asthma severity, however it is not
in itself a true marker of severe asthma; the score was only used as a
proxy in an attempt to explore the association of LUS findings with more
severe asthma. Finally, reliance upon parental and patient
questionnaires to gauge asthma severity and control may have introduced
recall bias, as asthma symptoms and severity are often under-recognized
by patients and parents.