We searched PubMed for articles containing the keyword, “asthma” in combination with “phenotypes”, “biomarkers”, “eosinophil”, “neutrophil”, “aspirin sensitive”, “allergic”, “corticosteroid resistance”, “exercise”, “extrinsic”, “intrinsic”, “severe exacerbation”. We made an effort to include only peer-reviewed publications. Selection for inclusion was on the basis of results that were reproducible or had support from other studies. No limit was placed on date or language of publication,
ReviewAsthma: defining of the persistent adult phenotypes
Section snippets
Phenotypic categories
Many categories have been used to define asthma phenotypes, mostly with general or clinical criteria. Although allergic and non-allergic asthma are probably the most commonly discussed phenotypes, the determination of additional phenotypes, is possible. This Review proposes to analyse the broad categories of phenotypes and classify them in three categories: phenotypes defined by clinical or physiological criteria; phenotypes related to environmental triggers; and phenotypes defined by their
Severity-defined asthma
Clinicians have identified many different asthma, phenotypes including those based on severity, liability (or not) of airflow restriction, response to therapy, and age at onset.6, 7, 8 National and international guidelines are the biggest proponents of phenotyping by severity with fairly stringent criteria to define four categories of asthma severity.6, 9 However, several publications have suggested that these definitions, which were developed on the basis of lung function, symptoms, and use of
Allergic asthma
Allergic sensitisation that triggers asthma might be the largest overall phenotype, especially in childhood asthma, but probably also in a high proportion of adults with asthma.45 As noted above, this phenotype can present at any age, but it commonly begins in early childhood. The acute pathobiology of this group has been studied extensively with allergen-challenge protocols. In some studies a relation to T helper type 2 (Th2) inflammatory reactions has been reported, although the evidence to
Inflammatory phenotypes
Perhaps the most important advance in the treatment of asthma has been the realisation that asthma pathology has an inflammatory component, which led to the widespread use of inhaled corticosteroids, and their rank as the gold-standard for asthma treatment. Early pathological studies of patients with mild asthma who were not treated with corticosteroids, recorded high numbers of eosinophils and lymphocytes in the large airway mucosa. The number of these cells decreased significantly in response
Additional pathological phenotypes
The description of pathological phenotypes of asthma is in its infancy. In the future, more specific biomarkers than we know about now will almost certainly be found that better discriminate phenotypes. However, only cysteinyl leukotrienes, and IgE, have been associated with an identifiable phenotype (aspirin-sensitive and allergic asthma, respectively) or a response to a targeted therapy such as anti-leukotriene therapy in children, and anti-IgE drugs.5, 55, 56, 112 An increased emphasis on
How does it all fit together?
Few studies have attempted to link different approaches to describing phenotypes in asthma. This is probably because of the insufficient pathological or immunological information available from large studies of asthma patients. As minimally invasive tests, such as exhaled nitric oxide and sputum analysis, become more commonplace, we will be able to link clinical, immunological and pathological characteristics of various asthma phenotypes. New approaches to statistical modeling, such as factor
Search strategy and selection criteria
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