SERIES: DIFFICULT ASTHMAPhenotype-specific treatment of difficult asthma in children
Section snippets
DEFINITION OF ASTHMA
The initial paediatric consensus statement defined asthma as ‘cough and/or wheeze in a context where asthma seems likely and other, rarer, diagnoses have been excluded’.1 This definition has the superb merit of not confusing pathological findings with clinical presentations, the importance of which has long been appreciated.2 In older children, the addendum that ‘asthma is a condition which causes airflow obstruction which varies over time and with treatment’ is entirely appropriate, although
WHAT DOES PHENOTYPE MEAN?
A phenotype may be considered as a cluster of either clinical or pathological features (not both, in our view) that tend to be associated and which are useful in some way, such as in managing the child or understanding the mechanisms of disease.5 There may be overlap between phenotypes and they may change over time. If the existence of phenotypes is proposed, the onus is on the proposer to justify the use of the term. The ‘so what?’ question is addressed at the end of this paper.
WHAT ARE THE COMPONENTS OF THE DIFFERENT ASTHMA PHENOTYPES?
The vast majority of children with asthma respond to low-dose inhaled corticosteroids with no side-effects. It is only in children with more problematic asthma that a discussion of phenotypes is profitable. The most important question is, what is it about this child and this child’s asthma that is different from the run-of-the-mill disease that is so easily treatable? In this context, we believe that it is helpful to consider components of the asthma syndromes to be:
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extent and nature of any
PHENOTYPIC APPROACH TO THE OLDER CHILD WITH SEVERE ASTHMA – IS IT WORTHWHILE?
We have proposed a largely pathological classification of severe asthma in childhood as a means for rationalising treatment. There is still much work to be done to try to work out the relationship between airway pathology and some clinical phenotypes, for example Types 1 and 2 brittle asthma. We have tested the utility of this approach in over 100 patients but larger studies are needed to confirm whether the invasive and expensive tests are worthwhile. Ultimately, we need to go from an
A PHENOTYPIC APPROACH TO ASTHMA – CONCLUSIONS
There has been an explosion of research into the basic mechanisms of asthma and we believe that this has clearly shown that there are different phenotypes which require a different approach to treatment. However, we have been slow to apply this knowledge in the clinic. There is a real need for studies to test the validity of the approaches discussed here. It is likely that a multi-centre and probably multi-national approach is needed if this is to be done. This seems to be the only way forward
PRACTICE POINTS
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If a child with asthma is not responding to simple treatment, it is important to ask what it is about this child and their asthma that makes it therapy resistant.
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There are several different subgroups of difficult asthma with different underlying causes.
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Consider separately the possible contributions of bronchial hyper-reactivity, airway inflammation and persistent airflow limitation to symptom persistence in severe asthma.
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Poor adherence to therapy and overperception of symptoms are important
RESEARCH DIRECTIONS
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What are the mechanisms of steroid-resistant, persistent airway inflammation in some cases of severe asthma?
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What are the mechanisms of persistent airway hyper-reactivity without residual inflammation?
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What is the relationship between airway inflammation and structural airway changes (remodelling)?
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Multi-centre studies are required to determine whether a phenotypic approach to severe asthma is worthwhile.
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