Asthma

Definition

Asthma is a chronic inflammatory disorder of the airways characterized by three core elements:

Reversible airway obstruction - narrowing of airways that can reverse spontaneously or with treatment
Airway inflammation - involving many different cell types
Bronchial hyperresponsiveness - an exaggerated reaction to a wide variety of stimuli

"Asthma is a chronic inflammatory disorder of the airways in which many different cells play a role. In patients with asthma, this inflammation causes breathlessness, chest tightness, recurrent episodes of wheezing, and cough, particularly at night."

Textbook of Family Medicine, 9th ed.

An important clinical reminder: not all wheezing is asthma, and not all asthma has wheezing.

Pathophysiology

The mechanism involves a cascade of events:

Step	What Happens
Trigger exposure	Allergens, irritants, exercise, infections stimulate the immune system
Airway inflammation	Mast cells, eosinophils, T lymphocytes, and macrophages release inflammatory mediators
Bronchoconstriction	Smooth muscle contraction narrows the airway lumen
Mucosal edema	Airway wall swelling further reduces airway diameter
Mucus hypersecretion	Excessive secretions block smaller airways
Air trapping	Obstruction is worst during expiration, leading to hyperinflation

Chronic asthma can also cause structural airway remodeling - subepithelial fibrosis, angiogenesis, and extracellular matrix deposition. This can make some obstruction less reversible over time.

Murray & Nadel's Textbook of Respiratory Medicine

Common Triggers

Environmental allergens: pollen, mold, house dust mites, cockroach excreta, animal dander
Respiratory infections (especially viral)
Exercise
Tobacco smoke, strong odors, air pollutants
Cold air / climate changes
Certain medications (aspirin, NSAIDs, beta-blockers)
Gastroesophageal reflux (GERD)
Emotional stress

Symptoms

Wheezing (high-pitched whistling sound during breathing)
Dyspnea (shortness of breath)
Chest tightness
Cough - often worse at night or early morning

Symptoms are characteristically variable and episodic.

Diagnosis

Diagnosis has three stages:

Suggestive symptoms with precipitating factors
Confirmation with testing (spirometry is the gold standard - looks for reduced FEV1/FVC ratio with reversibility after bronchodilator)
Symptomatic improvement with appropriate asthma therapy

Peak expiratory flow rate (PEFR) can be used for monitoring at home.

Differential Diagnosis to Consider

In Children	In Adults
Viral bronchiolitis	COPD
GERD	Congestive heart failure
Cystic fibrosis	Pulmonary embolism
Foreign body	ACE inhibitor-induced cough
Paradoxical vocal cord motion	Paradoxical vocal cord motion

Treatment (Stepwise Approach)

Treatment follows a step-up/step-down approach based on severity:

Reliever (rescue): Short-acting beta-2 agonists (SABAs) like salbutamol - for acute symptoms. Should be needed less than twice per week; if more frequent, step up therapy.
Controller (maintenance): Inhaled corticosteroids (ICS) are the preferred therapy for all persistent asthma - they address the underlying inflammation.
Add-on therapies: Long-acting beta-2 agonists (LABAs), leukotriene receptor antagonists (LTRAs), or biologics for severe/uncontrolled disease.
Acute exacerbations: Oral corticosteroids + nebulized SABAs + ipratropium (in the emergency setting).

Step therapy for adults with asthma showing stepwise progression of medications

Step therapy for adults with asthma. ICS = inhaled corticosteroid; LABA = long-acting beta-agonist; LTRA = leukotriene receptor antagonist; SABA = short-acting beta-agonist.

Epidemiology

Asthma affects approximately 26.8 million people in the United States
It is the most common chronic disease of childhood, affecting ~4.5 million children in the US
Prevalence increased from 1980 to 2010, but mortality and hospitalization rates have been declining since the late 1990s
Affects over 5.4 million people in the UK

Key Takeaways

Asthma = chronic airway inflammation + reversible obstruction + hyperresponsiveness
Most cases are triggered by allergens or irritants; often co-exists with allergic rhinitis
Spirometry is the diagnostic gold standard
Inhaled corticosteroids are the cornerstone of maintenance treatment
Good asthma control is achievable with proper identification of triggers and stepwise pharmacotherapy

Sources: Textbook of Family Medicine, 9th ed.; Murray & Nadel's Textbook of Respiratory Medicine

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