Rackemann was the first to introduce the concept of extrinsic/allergic and intrinsic/non-allergic asthma in 1947 and thus described the first phenotypes of asthma. Over recent decades, cluster analyses have confirmed that asthma is more of a heterogeneous disorder rather than just a single disease. Several phenotypes have been introduced in addition to the ones established 70 years ago,[2–6] but differentiating the phenotypes in clinical practice can be challenging. One of the answers appears to be the age of asthma onset and subsequently the division into childhood/early-onset and adult/late-onset asthma.[6,7]
Childhood asthma is commonly associated with allergy.[8,9] Large cohorts have shown allergic sensitization as a risk factor for development[10,11] and persistence of asthma in childhood. On the other hand, there is a lack of comprehensive studies on the relevance of allergy to adult asthma. Although allergic sensitization has been reported as a risk factor for asthma in adults[13,14] and adult-onset asthma, adult asthma is more often non-allergic than allergic.[7,16] Also, the rates of allergic sensitization in adult-onset asthma are mostly below 50%.[15–17] According to a recent Finnish cluster analysis, allergic asthma diagnosed in adulthood was often associated with respiratory symptoms already during childhood. However, contradicting results do also exist and a U.S.-based study reported only a slight difference in allergic sensitization in early- and late-onset asthma (72 and 63% in subjects with asthma onset before and after 40 years of age, respectively).
It appears that there is a lack of knowledge on the allergic and non-allergic phenotypes of adult-onset asthma and the relation between allergy and asthma onset age. Our aim was to study the association between asthma onset age and allergy by assessing age at diagnosis and age-specific incidence of asthma in adult asthmatics with and without allergic rhinitis in a population-based postal questionnaire study conducted in Finland.
BMC Pulm Med. 2020;20(9) © 2020 BioMed Central, Ltd.