The episodes are associated with airflow obstruction that is reversible either spontaneously or with treatment. The allergic type usually begins in childhood, is often seasonal, and is accompanied by an elevated, allergen-specific IgE level. Peak expiratory flow is decreased, and hypoxemia and hypercarbia occur in severe episodes. Fungi may be present. PMNs suggest infection.
Progressive disease is the exception.
Asthma is increasing in many countries. However, even in patients dying of asthma, airways are not uniformly involved, although bronchi are more uniformly involved than bronchioles. Bronchial arteries and veins are increased in number. Epithelium is hyperplastic with goblet cell or squamous metaplasia. Eosinophils and mast cells also infiltrate the epithelial layer.