CONSEQUENCES OF LONG-TERM INFLAMMATION: The Natural History of Asthma

The spectrum of clinical asthma is broad, ranging from occasional mild wheezing or coughing on exertion to severe, persistent disease that occasionally can be fatal. Asthma, by definition, is characterized by airway narrowing, which, at least initially, is fully reversible. 51 The course of asthma is characterized by apparent remission in some instances, and persistence and worsening in others. The effects of treatment on the "natural history" of asthma remain uncertain. The natural history of childhood asthma has been described in more than 50 studies. 24 Different outcomes have been reported, some studies suggesting that asthma improves or remits in adolescence and adulthood, and other studies reporting that most asthma persists, and may worsen with age. Some of the apparent conflict in the reported natural history of childhood asthma is related to the selection of the population in which the study is performed, the age of subjects when the cohort is first studied, the definition of asthma, the duration of follow-up, and the nature of the outcome assessments used. 52 The natural history of adult asthma has been less clearly defined, but remission is uncommon. This article focuses largely on studies of the natural history of asthma reporting objective functional outcomes, rather than only subjective outcomes, because cessation of symptoms does not necessarily assure return of normal airway caliber or responsiveness. 10,25,38,63