Asthma
Asthma is an obstructive lung disease characterised by episodic and reversible airway bronchoconstriction, as a result of airway inflammation and bronchial hyper-responsiveness. It's a Type 1 hypersensitivity reaction:
1st exposure to allergen induces mast cell sensitisation in which IgE binds to its IgE receptors
2nd exposure induces mast cell degranulation, leading to the release of inflammatory mediators e.g. histamine, prostaglandins, and leukotrienes
There’s resulting airway remodelling, characterised by bronchial smooth muscle hypertrophy, bronchoconstriction, mucous gland hypertrophy, vasodilation, and increased vascular permeability.
Risk factors for it includes:
Atopy - Asthma, Hayfever (allergic rhinitis), Eczema (atopic dermatitis)
Family hx
Overweight
Smoking
Triggers - Infection, Exercise, Animals, Allergens (pollen, dust mite), Cold/damp air, Dust, Strong emotions/laughter
Presentation
Presents with Wheeze, Dry cough, SOB, and Diurnal variation (typically worse at night)
O/E - Bilateral, widespread, polyphonic wheeze, Hyper-resonance on percussion, Hyperinflated chest
Features that would make asthma unlikely include:
Wheeze related to coughs and colds (viral-induced wheeze)
Unilateral wheeze (focal lesion/infection)
Isolated/productive cough
Non-responsive to bronchodilators
No obstructive changes on investigation
Investigations
The main investigations to do are:
Spirometry w/bronchodilator reversibility - Will show an obstructive pattern with an FEV1/FVC < 0.7, which will normalise after a bronchodilator is given
PEF - variability > 20% (diary of measurements can be kept for 2-4 weeks)
FeNO (Fractional exhaled nitric oxide) - 40+ in adults, 35+ in children - good indicator of level of airway inflammation
If there's still diagnostic uncertainty after initial tests, the patient can be offered a Direct bronchial challenge test with histamine/methacholine. With this, the patient breathes in gradually increasing doses of a medication that can irritate and constrict the airways. Those with sensitive lungs will be affected by a much lower dose than others.
Management
Non-pharmacological - Smoking cessation, Avoid precipitants, Review inhaler technique
Stepwise approach based on BTS guidelines:
SABA inhaler (reliever) + Low-dose ICS (preventer)
Add LABA
If little benefit - Continue LABA and increase ICS dose
If no benefit - Stop LABA and increase ICS dose
Trial of oral LTRA (e.g. montelukast), high-dose steroid, or oral B2-agonist
N.B. With NICE guidelines, the only difference is that the patient is given an LTRA before a LABA.