What is asthma?
Although physicians first recognised asthma over 1800 years ago, its definition has evolved over the last three decades as our understanding of underlying pathophysiology and different clinical presentations has developed.
The first written description of an asthma attack was by a Greek physician Aretaeus of Cappadocia in the second century of the Common Era. The word "asthma" comes from a Greek word "aazein" meaning "panting", but ancient Egyptian, Hebrew, Indian and other medical writings also refer to asthma.
During the 20th century, researchers thought that constriction of airway smooth muscle and excessive sensitivity of the airway to external stimuli (hyper-responsiveness) was the key feature of asthma. In the 1980s, it was recognised that airway inflammation was a cardinal feature, with structural changes in the airway (remodelling) present early in the development of disease.
Asthma remains one of the most important non-communicable diseases (NCDs). It is a cause of substantial disability and death worldwide. As such, asthma requires global attention and commitment to lessen its burden.
The definition and classification of asthma has been the subject of controversy for several decades. The Global Initiative for Asthma (GINA) describes asthma as "a heterogeneous disease, usually characterised by chronic airway inflammation. It is defined by the history of respiratory symptoms such as wheeze, shortness of breath, chest tightness and cough that vary over time and in intensity, together with variable expiratory airflow limitation". Although not strictly a definition, this description captures the essential features for clinical purposes.
For population-based studies, where doctor diagnosis is not practicable, questionnaires are the tool of choice. Questions about more recent symptoms (in the past 12 months) are more reliable than questions about symptoms in the past, because they reduce errors of recall. The most commonly used standard question is "Have you [has your child] had wheezing or whistling in the chest in the past 12 months?"; when the answer is "yes", the term "current wheeze" is commonly used, or "current asthma symptoms". However, asthma can cause other respiratory symptoms (Table).
A recent Lancet Commission has suggested a range of new ways of thinking about asthma, its mechanisms and its treatment, challenging conventional concepts of asthma as a single disease and proposing a more targeted approach. Notwithstanding these novel ideas, it remains clear that most people with asthma symptoms improve with asthma medicines, yet many lack access to these treatments (Chapter 10).
The use of the term asthma as a clinical diagnosis is still useful in most patients because it opens the door to appropriate management to reduce disease burden (Chapter 11). In low- and middle-income countries (LMICs), where most of the people often non-existent or out of reach.
There are two key asthma treatments: (i) bronchodilators (most commonly β2-agonists) that reverse airway narrowing by relaxing airway smooth muscle, and (ii) corticosteroids, which treat the underlying airway inflammation; inhaled corticosteroids (ICS) are known as preventers (called "controllers" by GINA). The inhaled route, with the use of a spacer, is the best way to administer both of these classes of medicines (Chapter 9). Inhalation is more effective and has fewer side effects than the oral route.
Acute asthma symptoms require shortacting β2-agonists (SABA). ICS are the first line asthma preventer for those with frequent or persistent symptoms. Most people diagnosed with asthma respond well to these forms of treatment, thus they are "asthma essential medicines" (Chapter 10).
Recently the World Health Organization (WHO) added an ICS/long-acting β2-agonist (LABA) combination to its Essential Medicines List. Asthma management guidelines specify using ICS/LABA medicines to control persistent or difficult-to-treat asthma. Moreover recent research suggests their role in asthma treatment is likely to expand.
Is asthma an allergic disease?
Asthma is often described as an allergic disease in which allergens (such as pollens, mites or cockroaches) or certain workplace exposures can trigger attacks of airway narrowing and, through continued exposure, lead to airway inflammation and enhanced airway responsiveness. However, this paradigm came from observations predominantly in western high-income countries, and the association between allergy and asthma is much weaker in LMICs. Some occupational causes of asthma do not appear to involve allergy. It is now widely recognised that allergic mechanisms are involved in half, or less, of the people with asthma. In many people, asthma probably involves non-allergic inflammation of the airways, although we do not understand well the mechanisms involved.
Course of asthma over the lifespan
It is not possible to define a single natural history for asthma and it can develop at any stage in life, including adulthood. However, asthma symptoms most commonly develop for the first time in early childhood. Young children of pre-school age often wheeze with viral infection, but only about half of them go on to have characteristic asthma at school age. Children who have frequent or persistent wheeze are more likely to have evidence of airway inflammation and remodelling, impaired lung function, and persistently troublesome symptoms into adulthood. Recent reports raise the possibility that childhood asthma, persisting into adulthood, may predispose people to chronic obstructive pulmonary disease (COPD).
The definition and understanding of asthma has developed since the 1980s, with new ways of thinking about asthma recently proposed. It is vital that asthma essential medicines of proven benefit are accessible for all people who have asthma symptoms. At the same time, commitment to research that increases the understanding of asthma and its causes, and leads to improvements in asthma management are essential.