The prevalence of asthma has increased over the past 20 years and it continues to be a common problem throughout the world. Considerable advances have been made in understanding the genetics, epidemiology and pathophysiology of asthma, new treatments have been devised and older treatments refined. A small minority of patients have a form of asthma that is very difficult to control but the majority of patients can obtain very good control with standard medications. A number of studies have shown that many patients do not achieve this degree of control. Management of chronic conditions such as asthma is a partnership between patients, families and their doctors and nurses in primary care. This sixth edition of the ABC of Asthma deals with recent advances and also contains new chapters that deal with the management of asthma in general practice. We hope that it will help health professionals dealing with asthma and lead to real improvements in the lives of people with asthma. Asthma is an overall descriptive term but there are a number of more or less distinct phenotypes which may have different causes, clinical patterns and responses to treatment. The clinical picture of asthma in young adults is recognisable and reproducible. The difficulties in precise diagnosis arise in the very young, in older groups and in verymild asthma. Breathlessness from other causes, such as increased tendency towards obesity, may be confused with asthma. The clinical characteristic of asthma is airflow obstruction, which can be reversed over short periods of time or with treatment. This may be evident from provocation by specific stimuli or from the response to bronchodilators.
The airflow obstruction leads to the usual symptoms of shortness of breath. The underlying pathology is inflammatory change in the airway wall, leading to irritability and responsiveness to various stimuli and also to coughing, the other common symptom of asthma. Cough may be the only or first symptom of asthma. Asthma has commonly been defined on the basis of wide variations in resistance to airflow over short periods of time. More recently, the importance of inflammatory change in the airways has been recognised. There is no universally agreed definition but most contain the elements from the Global Initiative for Asthma. Low concentrations of non-specific stimuli such as inhaled methacholine and histamine produce airway narrowing. In general, the more severe the asthma, the greater the inflammation and the more the airways react on challenge. Other stimuli such as cold air, exercise and hypotonic solutions can also provoke this increased reactivity. In contrast, it is difficult to induce significant narrowing of the airways with many of these stimuli in healthy people. In some epidemiological studies, increased airway responsiveness is used as part of the definition of asthma. Wheezing during the past 12 months is added to the definition to exclude those who have increased responsiveness but no symptoms.[/mks_toggle]