Phenotypic differences between pediatric and adult asthma.
The goal of asthma phenotyping is to understand disease mechanisms or optimize management. Phenotypes show age-related variation. The phenotypes of wheezing in the first year of life are little studied; many remit in the second year of life, and the children who remit do not have later-onset wheeze, as far as is known. Preschool wheeze is optimally phenotyped by symptom pattern, defined as either episodic viral or multiple-trigger wheeze, which allows rational treatment planning. In school age and adult life, most patients with mild asthma can be managed adequately without phenotyping, but severe asthma clearly falls into several phenotypic groups. Children with severe asthma have no gender bias and are highly atopic with relatively well-preserved lung function, in contrast to the female-preponderant, non-atopic bias seen in adults. Phenotyping has been mainly by proximal luminal cellularity. However, this does not take account of any variation of cellularity over time, distal airway changes, or the relative contribution of mucosal and luminal inflammatory changes. There may be a separate exacerbating phenotype, characterized by airway eosinophilia. Particular adult phenotypes include late-onset asthma and a phenotype characterized by progressive loss of lung function, but critical review suggests that these phenotypes may also have childhood roots. Longitudinal data are needed to determine the stability of phenotypes and their prognoses. Retrospective recall of childhood events is of limited value. In conclusion, a full understanding the multifaceted phenotypes of asthma requires a thorough knowledge of early life events and their consequences over many decades.