Asthma phenotypes and endotypes: an evolving paradigm for classification.

Asthma is a common chronic disease characterized by intermittent chest symptoms, variable airways obstruction, and bronchial hyperresponsiveness. Research performed over the past one to two decades has sought to better understand the heterogeneous clinical nature of asthma. Whereas older attempts at phenotyping asthma emphasized the duality of allergic vs. non-allergic asthma, more recent non-biased analyses have attempted to cluster patients by a multitude of possible features, including age of onset, atopy, severity of airways obstruction, and requirement for medication. Examples of these phenotypes include early-onset mild allergic asthma, later-onset asthma associated with obesity, and severe non-atopic asthma with frequent exacerbations. The elucidation of asthma phenotypes has been further refined by including information regarding pathophysiologic mechanisms present in different groups. These groups, called endotypes, include examples such as aspirin-exacerbated respiratory disease and allergic bronchopulmonary mycosis. A growing understanding of these mechanistically distinct groups, along with the identification of relevant cellular or molecular biomarkers, is already showing promise as a way of predicting clinical response to various asthma therapies. As the number of targeted treatments for asthma continues to grow, physicians will have the opportunity to practice an individualized approach to diagnosis and treatment, which will hopefully improve asthma outcomes and quality of life for these patients.