The natural history of asthma

Abstract

The natural history of asthma in a population is for the peak prevalence to be in childhood followed by decline in the second and third decades and then an increasing prevalence throughout adulthood. Males are more often affected before adolescence and females in adulthood. Bronchial hyperresponsiveness to nonspecific stimuli is a characteristic feature of asthma and is, in part, genetically determined. In population studies, bronchial hyperresponsiveness appears to be approximately twice as common as clinical asthma. Episodic wheezing and dyspnea may be precipitated in these predisposed individuals by, among other things, respiratory infections, chronic passive exposure to cigarette smoke in childhood, and the development of allergy to environmental allergens. A sizeable group of those developing asthma in adulthood are subjects who had asthma in childhood that remitted for a variable number of years, then relapsed. Remissions are uncommon in adult asthma and are most common in patients with mild asthma. Asthma with onset in late adulthood may be characterized initially by chronic cough, especially in subjects who have smoked tobacco. Nevertheless, characteristic features of asthma are usually present including nocturnal awakening with wheezing, sputum eosinophilia, and significant reversal of bronchial obstruction with corticosteroid therapy. With prolonged and severe asthma, irreversible obstruction may develop even in those individuals who had never smoked. This irreversible component appears to be due to fixed airway obstruction and not to the development of emphysema.