Allergic vs nonallergic asthma: what makes the difference?

BACKGROUND The aim of this work was to describe clinical similarities and differences between allergic and nonallergic asthmatics, notably concerning the nasosinusal involvement. METHODS A total of 165 asthmatics (122 allergics and 43 nonallergics) and 193 controls (40 allergics and 153 nonallergics), recruited in the frame of EGEA study (Epidemiological study on the Genetics and Environment of Asthma, bronchial hyperresponsiveness and atopy), were included. Asthmatics were included on the basis of positive answer to four standardized items. To establish differences and similarities between allergic and nonallergic asthmatics, general characteristics (age, sex, smoking habits, history of hay fever and allergic dermatitis), history of asthma, severity and nasosinusal involvement were examined. Clinical assessment was based on the answers to a detailed questionnaire, and spirometry. RESULTS Greater age, female sex, sinusal polyposis, and FEV1 below 80% of the predicted value increased the risk of displaying a nonallergic type of asthma, whereas history of hay fever, seasonal exacerbation of asthma, and asthma duration lowered this risk. Unexpectedly, we found no difference in terms of rhinitic symptoms between both groups, probably resulting from distinct causes. CONCLUSION These results give new insights into the contrasts between clinical features of allergic and nonallergic asthma. The terminology of extrinsic asthma was first introduced by Rackeman in 1947 (1) and referred to the triggering role of allergens in asthma. By symmetry, he described intrinsic asthma as a disease characterized by later onset in life, female predominance, higher degree of severity, and more frequent association to nasosinusal polyposis. As these asthmatics were not improved by conventional treatment, this author considered their disease as caused by a nonallergic, unknown phenomenon. It is now widely admitted that nonallergic asthma can be objectively distinguished from allergic asthma based on negative skin tests to usual aeroallergens. On the other hand, positive skin test shows a tendency to produce IgE antibodies in response to low doses of allergens. "Atopy" and "atopic" are the terms used to describe this clinical trait and predisposition (2). Allergic clinical manifestations of atopy are of various types, for example rhinitis and asthma. Nowadays the terminology of "extrinsic" and "intrinsic" asthma should no longer be used, and should be replaced by the terminology of "allergic" or "nonallergic" asthma (2).