Exercise-induced bronchoconstriction — formative SAQs

SAQ 1 — The school-age child who wheezes with sport (20 marks, ~15 minutes)

An 8-year-old boy is referred because he coughs and wheezes when he runs. His mother says the trouble starts a few minutes into a game and is worst just after he stops, then eases with rest over half an hour. He has eczema, and he coughs at night in winter. Between episodes he is well and his chest is clear today. He has borrowed a friend's blue inhaler once or twice and felt it helped. ^[3]

Questions

1. Give the most likely diagnosis and the features in this history that support it. (4 marks) ^[3]
2. He is 8 years old. State the single most useful confirmatory investigation, the result that would confirm the diagnosis, and why a normal resting spirometry would not exclude it. (5 marks) ^[10]
3. Explain the mechanism by which exercise narrows his airway. (4 marks) ^[5]
4. Outline your management plan, naming the most important first step and the role of a pre-exercise reliever. (5 marks) ^[12]
5. State the danger in relying on a daily short-acting beta-agonist to get through sport. (2 marks) ^[5]

Model answer (must-hit)

1. The most likely diagnosis is exercise-induced bronchoconstriction, most probably as part of asthma. Supporting features are the characteristic timing (symptoms a few minutes into exercise, worst after stopping, settling with rest over about thirty minutes), the exercise trigger, the personal atopy (eczema) and nocturnal winter cough suggesting underlying asthma, the normal chest between episodes, and the reported benefit from a bronchodilator. ^[3]
2. The single most useful confirmatory investigation is an objective challenge test measuring the fall in FEV1 — a standardised exercise challenge or eucapnic voluntary hyperpnoea, which he is old enough to perform. The result that confirms the diagnosis is a fall in FEV1 of ten percent or more from baseline after the challenge. A normal resting spirometry does not exclude it because the airway is open between episodes; the diagnostic value lies in the provocation, not the baseline. ^[10]
3. Exercise makes him breathe large volumes of cold, dry air through the mouth, bypassing nasal conditioning. The airway lining loses water warming and humidifying this air, and the airway surface liquid becomes hyperosmolar. This osmotic stress activates airway mast cells to release histamine, cysteinyl leukotrienes and prostaglandin D2, which contract airway smooth muscle and cause mucosal swelling and mucus, narrowing the airway transiently before it recovers. ^[5]
4. The most important first step is to control the underlying asthma with a regular inhaled corticosteroid, because in most children exercise symptoms signal inadequate control; I would also check adherence and inhaler technique. Non-drug measures — a warm-up before exercise, warming inspired air with a scarf in the cold, and avoiding the worst conditions — are added for every child. A pre-exercise short-acting beta-agonist taken ten to fifteen minutes before exercise covers breakthrough symptoms and protects for two to three hours. The goal is full participation in sport. ^[12]
5. Daily use of a short-acting beta-agonist induces tolerance and reduces its bronchoprotective effect, so the child loses the very protection they depend on; daily need is also a marker of poor control and should prompt stepping up the controller rather than supplying more reliever. ^[5]