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COPD emphysema pathology diagram
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Asthma & COPD: A Comprehensive Overview
1. Definitions
| Feature | Asthma | COPD |
|---|---|---|
| Core defect | Reversible airway hyperresponsiveness | Irreversible (or poorly reversible) airflow obstruction |
| Key subtypes | Atopic, non-atopic | Emphysema, chronic bronchitis (often coexist) |
| Progression | Usually NOT progressive | Progressive, especially with continued smoking |
| Typical age of onset | Often childhood/young adult | >40 years, typically |
2. Pathophysiology
Asthma
Airflow obstruction in asthma results from three concurrent mechanisms:
- Bronchial smooth muscle contraction (bronchoconstriction)
- Bronchial wall inflammation
- Increased mucus secretion
Atopic (allergic) asthma — a Th2/IgE-mediated reaction to environmental allergens:
- Early-phase reaction: mast cell degranulation → histamine, leukotrienes → immediate bronchoconstriction
- Late-phase reaction: eosinophil/lymphocyte infiltration driven by Th2 cytokines (IL-4, IL-5, IL-13)
Non-atopic asthma triggers: viral infections, cold air, exercise, pollutants.
Key inflammatory cells: eosinophils (virtually all subtypes) — eosinophil products such as major basic protein cause airway damage.
Airway remodeling: if untreated, subbasement membrane thickening + bronchial gland/smooth muscle hypertrophy can add an irreversible component.
— Robbins & Kumar Basic Pathology, Lippincott Pharmacology
COPD
COPD encompasses two often-coexisting entities:
Emphysema
- Enlarged air spaces distal to terminal bronchioles from destruction of elastic support by proteases (especially from neutrophils)
- Loss of elastic recoil → expiratory collapse, air trapping, static and dynamic hyperinflation
- Subtypes: centriacinar (most common; smoking-related) vs. panacinar (α₁-antitrypsin deficiency)
- Clinical hallmarks: barrel chest, dyspnea, relatively preserved oxygenation at rest ("pink puffer")
Chronic Bronchitis
- Defined clinically: productive cough ≥3 consecutive months/year for ≥2 consecutive years
- Pathology: hyperplasia of mucus-secreting glands, goblet cell metaplasia, small airway inflammation (chronic bronchiolitis), bronchiolar wall fibrosis
- Mucus concentrations of MUC5AC are increased 10-fold in severe COPD
- Tends to develop hypoxemia and hypercapnia ("blue bloater")
Inflammatory profile comparison:
| Asthma | COPD | |
|---|---|---|
| Dominant cells | Eosinophils, mast cells, Th2 lymphocytes | Neutrophils, macrophages, CD8+ T cells |
| Cytokines | IL-4, IL-5, IL-13 | IL-8, TNF-α, IL-1β |
| Response to ICS | Excellent | Moderate (especially if eosinophilic) |
— Katzung's Basic and Clinical Pharmacology, 16th Ed.
3. Spirometry
Both conditions cause obstructive pattern on spirometry:
- ↓ FEV₁
- Normal or near-normal FVC
- ↓ FEV₁/FVC ratio (<0.70 post-bronchodilator = diagnostic criterion for COPD per GOLD)
Key distinction: In asthma, obstruction is reversible (≥12% and ≥200 mL improvement in FEV₁ after bronchodilator). In COPD, obstruction is not fully reversible.
4. Treatment
Asthma (GINA Guidelines)
| Symptom Frequency | Preferred Controller | Reliever |
|---|---|---|
| <2×/month | Low-dose ICS-formoterol as needed | — |
| >2×/month, <daily | Low-dose ICS-formoterol as needed | — |
| Most days / weekly nocturnal | Low-dose maintenance ICS-formoterol | Low-dose ICS-formoterol PRN |
| Daily symptoms / low lung function | Medium-dose maintenance ICS-formoterol | Low-dose ICS-formoterol PRN |
Key drug classes:
- Inhaled corticosteroids (ICS) — cornerstone; inhibit phospholipase A2 → ↓ arachidonic acid release → anti-inflammatory. Low oral bioavailability is critical (fluticasone ~1%, mometasone <1%)
- SABA (e.g., albuterol/salbutamol) — acute relief
- LABA (e.g., formoterol, salmeterol) — always combined with ICS in asthma
- Biologic agents (for severe/refractory disease): dupilumab (anti-IL-4Rα), mepolizumab (anti-IL-5), omalizumab (anti-IgE)
COPD (GOLD Guidelines)
- Stop smoking — single most important intervention
- SABA (albuterol) or short-acting anticholinergic (ipratropium) — acute symptom relief
- LAMA (tiotropium, umeclidinium) — preferred long-acting maintenance; reduces exacerbations and dynamic hyperinflation
- LABA (salmeterol, formoterol, indacaterol) — alternative/additive to LAMA
- ICS — reserved for: severe obstruction, frequent exacerbations, high blood eosinophil count (≥300 cells/μL favors ICS response); ICS increases risk of bacterial pneumonia in COPD
- Roflumilast (PDE4 inhibitor) — reduces exacerbation frequency in severe COPD with chronic bronchitis phenotype
- Antibiotics during exacerbations (β-lactams, doxycycline, azithromycin — targeting H. influenzae)
— Katzung's Basic and Clinical Pharmacology, 16th Ed.
5. Asthma-COPD Overlap (ACO)
Not a distinct syndrome but a clinically useful concept when patients exhibit features of both conditions simultaneously.
Key points from Harrison's (2025):
- Smoking can blunt the response to ICS in asthmatics
- Dupilumab has been approved for COPD patients with recurrent exacerbations and elevated eosinophils
- Earlier initiation of anticholinergics may be warranted in patients with both conditions
- Blood eosinophil count is now the preferred biomarker for guiding ICS use in COPD (replacing the older asthma-COPD overlap framework)
— Harrison's Principles of Internal Medicine, 22nd Ed. (2025)
6. Key Distinguishing Features at a Glance
| Feature | Asthma | COPD |
|---|---|---|
| Age of onset | Often young | >40 years |
| Smoking history | Not required | Major risk factor |
| Airflow obstruction | Reversible | Irreversible (or minimally reversible) |
| Main inflammation | Eosinophilic / Th2 | Neutrophilic |
| ICS response | Excellent | Moderate (eosinophil-dependent) |
| Progression | Non-progressive | Progressive |
| FEV₁ post-BD | Normalizes | Does not normalize |
| Exacerbation triggers | Allergens, exercise, URIs | URIs, air pollution, bacteria |
| Cor pulmonale | Rare | Common in advanced disease |
Sources: Robbins & Kumar Basic Pathology; Lippincott Illustrated Reviews: Pharmacology; Katzung's Basic and Clinical Pharmacology 16e; Fishman's Pulmonary Diseases and Disorders; Murray & Nadel's Textbook of Respiratory Medicine; Harrison's Principles of Internal Medicine 22e (2025)
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