The word “usually” in the definition of asthma has concerned some readers. The rationale is that, although chronic airway inflammation is characteristic of most currently known asthma phenotypes, the
absence of inflammatory markers should not preclude the diagnosis of asthma being made in patients with variable expiratory airflow limitation and variable respiratory symptoms. This should not be taken to suggest a lesser emphasis on anti-inflammatory treatment; on the contrary, as described below, indications for inhaled corticosteroid (ICS) treatment have been expanded. Importantly, the definition also avoids past assumptions about the relationship between airway inflammation, airway hyperresponsiveness, symptoms and exacerbations, and the inclusion of heterogeneity in the definition reinforces the need for ongoing research to identify specific treatment targets