Evolving Concepts in Asthma

Paul M. O'Byrne, MB, FRCP(C), FRSC

Remarkable advances in the diagnosis and management of asthma have been made over the past four decades. The recognition of the efficacy and safety of inhaled corticosteroids (ICS) in asthma management; the development of other treatment options, such as leukotriene receptor antagonists; and the added value of adding an inhaled long-acting β₂-agonist (LABA) to ICS, when ICS alone are not providing optimal management, have provided a range of treatment options that can provide asthma control to most patients.

Another important advance in asthma management has been that all treatment guidelines agree that the primary goal of management is to achieve optimal asthma control. This consists of two domains: optimizing current (day-to-day) control, defined as the minimization of both daytime and nighttime symptoms, no limitation of activity, minimal rescue bronchodilator use and no airway narrowing; and minimizing future risk, defined by long-term decline in lung function, severe asthma exacerbations, and unwanted effects from medications.

Despite the clarity around management objectives, and the availability of effective and safe medications, many asthmatic patients remain poorly controlled. The most important reason for this is poor adherence to treatment. There are also asthmatic patients who, despite treatment with optimal doses of asthma medications, have uncontrolled asthma and are at risk of severe asthma exacerbations. The use of combination of ICS/LABA reduces exacerbation risk. In addition, phenotyping with relation to atopic status, and the type of airway inflammation present, particularly eosinophilic inflammation, may provide additional useful information with regard to newer treatment options, which are biologic treatments directed against immunoglobulin E (IgE), or interleukin (IL)-5, or IL-4Rα.

The current issue of Seminars in Respiratory and Critical Care Medicine examines a variety of evolving concepts in asthma epidemiology, pathobiology, and management. The prevalence of asthma has increased in many countries over the past 20 to 30 years and there is a wide disparity in prevalence in different countries and in different ethnic groups. Subbarao et al identify socioeconomic status, environmental exposures, the host microbiome, and genetics as potential causes. The many environmental causes of asthma, often labeled as “inducers,” and triggers of asthma symptoms, called “inciters,” such as exercise, are compared and contrasted in chapters by Cockcroft and Boulet et al.

The greatest risk to asthma patients is the development of severe asthma exacerbations. The use of phenotyping and biomarkers to identify “at risk” asthmatic children is detailed by Anderson and Szefler, and a description of the most up-to-date knowledge of the most common cause of severe exacerbations, respiratory viruses, is provided by Wark et al. The consequence of the environmental inducers and exposure to respiratory viruses is the development of airway inflammation. The most recent information on pathobiology of this inflammatory response and the use of biomarkers to measure these responses is covered in chapters by Lim and Nair and its immunology by Tung et al.

Finally, the most recent knowledge on asthma management is covered in four chapters. Asthma during pregnancy, which can be a particularly challenging management problem for asthmatic women, is reviewed by Namazy and Schatz. The evidence basis for asthma treatment recommendations is reviewed by Reddel; the causes and identification of severe refractory asthma, not responding to conventional therapies (between 5% and 8% of all asthmatics), are discussed by Chung; and the most recent additions to the armamentarium of asthma treatment, the biologic treatments are reviewed by Viswanathan and Busse.

This issue of Seminars has very comprehensively covered all of the most relevant topics, and reviewed the most current understanding of the epidemiology, pathobiology, and treatment of asthma. I would like to thank the contributors for sharing their knowledge and expertise and for making this such a useful addition to the Seminars series.