How do you differentiate between asthma and airway reactive disease?

Differentiating Asthma from Reactive Airway Disease

"Reactive airway disease" is not a distinct diagnosis but rather a descriptive term for bronchospasm without confirmed asthma; the key distinction is that asthma requires documented reversible airflow obstruction or airway hyperresponsiveness, while reactive airway disease is often used when objective testing is pending or unavailable. 1

Clinical Approach to Diagnosis

Step 1: Confirm Reversible Airflow Limitation with Objective Testing

The diagnosis of asthma is fundamentally clinical but must be corroborated by objective lung function testing whenever possible 1. The term "reactive airway disease" is often used when patients present with respiratory symptoms but lack objective confirmation.

Essential objective measures include:

• Spirometry with bronchodilator response: FEV₁ improvement ≥12% AND ≥200 mL after bronchodilator strongly suggests asthma 1
• Peak expiratory flow (PEF) variability: ≥20% variability with minimum change of 60 L/min is highly suggestive of asthma 2
• Bronchoprovocation testing: Confirms airway hyperresponsiveness when spirometry is normal between episodes 1, 2, 3

A critical pitfall: Airflow limitation may be completely normal between episodes of bronchospasm 2. This is why a history of wheeze alone has only 35% predictive value for asthma, and even expiratory wheezing on examination has only 43% predictive value compared to methacholine challenge 3.

Step 2: Assess Symptom Pattern and Characteristics

Classic asthma symptoms are:

• Variable and intermittent
• Worse at night or early morning
• Provoked by specific triggers (exercise, allergens, cold air, irritants)
• Include wheeze, shortness of breath, chest tightness, and cough 1

Important distinction: When cough is the predominant symptom without wheeze, this is termed "cough variant asthma" and should be managed as asthma with inhaled corticosteroids and bronchodilators 1, 2. The absence of wheezing does not exclude reactive airway disease or asthma 2.

Step 3: Differentiate from Other Conditions

Must exclude alternative diagnoses that can mimic asthma:

• COPD (especially in smokers >40 years)
• Vocal cord dysfunction or mechanical upper airway obstruction
• Cardiac dysfunction
• Cystic fibrosis
• Allergic bronchopulmonary aspergillosis 1

Key differentiating features:

• Asthma: High or high-normal DLCO, reversible obstruction, eosinophilia 1
• COPD: Low DLCO, incompletely reversible obstruction, smoking history 1
• Reactive Airways Dysfunction Syndrome (RADS): Acute onset after single high-level irritant exposure, generally shows less reversibility (only 13% show ≥20% FEV₁ improvement) compared to occupational asthma (40%) 4, 5

Step 4: Assess for Asthma-COPD Overlap

When features of both asthma and COPD are present, consider asthma-COPD overlap syndrome (ACOS) 1:

GINA/GOLD criteria suggest overlap when:

• Similar number of asthma and COPD features are present
• FEV₁ improvement ≥15% AND ≥400 mL (major criterion)
• Sputum eosinophilia ≥3% (major criterion)
• History of childhood asthma with smoking history (major criterion)
• Elevated total IgE, atopy history, or bronchodilator response ≥12% AND ≥200 mL on multiple occasions (minor criteria) 1

Two major criteria OR one major plus two minor criteria strongly suggest overlap 1.

Step 5: Investigate Concomitant Conditions

Essential workup includes:

• Allergen skin testing for atopy and allergic rhinitis
• CT sinuses if chronic rhinosinusitis suspected
• 24-hour esophageal pH monitoring for gastroesophageal reflux
• Blood eosinophil count and total IgE
• Chest radiograph to exclude infiltrates or structural abnormalities 1

Management Implications

For confirmed asthma or cough variant asthma:

• Short-acting beta-agonists (SABA) for symptom relief
• Daily inhaled corticosteroids (ICS) as controller therapy for persistent symptoms
• Add long-acting beta-agonist (LABA) for moderate-severe persistent symptoms in patients ≥4 years 2

For asthma-COPD overlap:

• Initiate combination ICS/LABA therapy
• Consider triple therapy with LAMA as disease severity increases 1

Critical Pitfalls to Avoid

• Never rely on clinical history or wheeze alone to diagnose asthma—objective testing is essential 3
• Normal lung function between episodes does not rule out reactive airway disease—PEF monitoring or bronchoprovocation testing may be needed 2
• Overreliance on bronchodilators without addressing underlying inflammation leads to poor symptom control 2
• Failure to recognize that "reactive airway disease" is a temporary descriptor, not a final diagnosis—pursue objective confirmation 1, 2