Introduction
Asthma is chronic inflammation of the airways that makes them twitchy and narrow from time to time. It shows as recurrent wheeze, cough (often at night), chest tightness and breathlessness that vary over time and reverse, by themselves or with treatment. It is the commonest chronic disease of childhood (about 1 child in 10).
Why it happens
- Inflammation, usually type 2: mast cells, eosinophils, Th2 cells, IgE, interleukins 4, 5 and 13.
- Bronchospasm, mucosal oedema and thick mucus plugs narrow the airway; long-standing disease remodels the wall.
- Risk factors: atopy (eczema, allergic rhinitis, food allergy), parents with asthma, smoking in pregnancy and at home, prematurity, obesity.
- Triggers: viral colds (the commonest), exercise, cold air, allergens (house dust mite, pets, pollen, moulds), smoke, pollution, emotion.
Wheeze in pre-school children
Many toddlers wheeze only with colds (episodic viral wheeze) and grow out of it; others wheeze with many triggers and between colds (multiple-trigger wheeze), which is more likely to be asthma, especially with eczema or a parent with asthma. Under 5 years the diagnosis is clinical: a pattern of symptoms and a good response to a trial of inhaled steroid.