Asthma: Diagnosis and Control — MCCQE Notes

Diagnosis needs objective proof

Symptoms alone are not enough. Demonstrate variable expiratory airflow limitation:

• Spirometry showing obstruction (FEV₁/FVC below the lower limit of normal) with reversibility: FEV₁ improving by ≥ 12% and ≥ 200 mL after a bronchodilator
• If spirometry is normal, a methacholine challenge — a negative test largely excludes asthma, which makes it most useful for ruling out
• Peak flow variability over two weeks as a lower-tech alternative

In children under 6, diagnosis is clinical, based on recurrent symptom patterns and response to treatment.

Assessing control

Poor control is any of:

• Daytime symptoms more than twice a week
• Any night-time waking from asthma
• Reliever use more than twice a week (not counting pre-exercise)
• Any limitation of activity
• Any exacerbation needing oral steroids in the past year

Before escalating therapy for poor control, always check the three things that explain most of it: inhaler technique, adherence, and triggers (allergens, smoking, occupational exposure, reflux, rhinitis, beta-blockers, NSAIDs in aspirin-sensitive disease).

Treatment structure

The key modern change: short-acting beta-agonist alone is no longer appropriate maintenance therapy at any severity, because it treats symptoms while inflammation progresses.

1. As-needed low-dose ICS–formoterol, or an inhaled corticosteroid taken whenever the reliever is taken
2. Daily low-dose ICS plus as-needed reliever
3. Low-dose ICS–LABA, ideally as single-inhaler maintenance and reliever therapy
4. Medium-dose ICS–LABA; consider adding a LAMA (tiotropium) or a leukotriene receptor antagonist
5. Specialist referral: high-dose combination, phenotype the patient, and consider biologics — anti-IgE (omalizumab) for allergic asthma, anti-IL-5 (mepolizumab, benralizumab) for eosinophilic asthma

A LABA is never used without an inhaled corticosteroid — that combination increases asthma deaths.

Acute exacerbation

• Oxygen to saturations of 93–95%
• Salbutamol by metered-dose inhaler with spacer or nebuliser, with ipratropium in moderate-to-severe attacks
• Systemic corticosteroids for essentially everyone, within an hour, continued 5–7 days with no taper needed for short courses
• Magnesium sulphate IV in severe attacks not responding
• Reassess with peak flow or FEV₁, not with wheeze — a silent chest is an ominous sign, not an improving one
• A normal or rising PaCO₂ in an acutely breathless asthmatic signals exhaustion and impending respiratory failure

Before discharge

Oral steroid course, check inhaler technique, an action plan in writing, and follow-up within 2–7 days. The exacerbation itself is the marker that maintenance therapy needs review.