Asthma

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Asthma  

Definition:
A heterogeneous chronic inflammatory airway disease characterized by variable respiratory symptoms (wheeze, dyspnea, chest tightness, cough) and variable expiratory airflow. Symptoms may fluctuate, and airflow limitation may become persistent in advanced stages.

Triggers: Cold air, allergens (pollen, dust mites, foods), viral infections, medications (e.g., aspirin, NSAIDs, beta-blockers), exercise.

Phenotypes:

  • Allergic (extrinsic) asthma: Childhood onset, triggered by allergens, associated with atopy.

  • Nonallergic (intrinsic) asthma: Adult-onset (>40 years), often triggered by infections, cold air, or irritants; less responsive to ICS.

  • Adult-onset asthma: Typically nonallergic.

  • Cough variant asthma: Chronic dry cough.

  • Aspirin-exacerbated respiratory disease (AERD): Samter triad.

  • Asthma-COPD overlap: Features of both diseases.

  • Occupational asthma: Triggered by workplace allergens/irritants.

  • Obesity-associated asthma: Prominent symptoms with minimal eosinophilic inflammation.

Epidemiology

  • Prevalence: 5–10% in the US.

  • More common in Black individuals.

  • Age/Sex distribution:

    • <18 years: ♂ > ♀

    • 18 years: ♀ > ♂

  • Allergic asthma: usually childhood onset

  • Nonallergic asthma: typically adult onset (>40 years)

Pathophysiology

Common mechanisms:

  • Th2-cell–driven inflammation → cytokines (IL-3, IL-4, IL-5, IL-13) → eosinophil activation & IgE production

  • Bronchial hyperresponsiveness, inflammation, and obstruction due to:

    • Bronchospasm

    • Mucosal edema

    • Increased mucus secretion

    • Goblet cell hyperplasia

    • Smooth muscle hypertrophy

Type-specific mechanisms:

  • Allergic asthma: IgE-mediated hypersensitivity

  • Nonallergic/irritant asthma: Neutrophilic inflammation, COX-1 inhibition in AERD

Clinical Features

  • Typical: Wheezing (end-expiratory), dyspnea, chest tightness, cough (worse at night/exercise), hyperresonance on percussion, prolonged expiratory phase.

  • Atypical: May present as chronic cough only or overlap with comorbid conditions (rhinitis, eczema).

  • Acute exacerbation: Sudden worsening; life-threatening in severe cases.

Diagnosis

Gold standard: Pulmonary function tests (PFTs: spirometry or peak expiratory flow) showing variable expiratory airflow.


Supportive tests:

  • Biomarkers: ↑ FeNO, ↑ blood eosinophils

  • Allergy testing: Skin prick or serum IgE

  • Imaging: HRCT (usually normal; may show air trapping)

  • Sputum analysis: Curschmann spirals, Charcot-Leyden crystals, Creola bodies

Differential diagnoses: COPD, cystic fibrosis, bronchiectasis, interstitial lung disease, vocal cord dysfunction, GERD, ACE-inhibitor cough, etc.

Asthma Severity (GINA / NAEPP)

SeveritySymptomsLung functionExacerbations
Intermittent≤2 days/weekFEV1 >80%≤1/year
Mild persistent3–6 days/weekFEV1 ≥80%≥2/year
Moderate persistentDailyFEV1 60–79%-
Severe persistentThroughout the dayFEV1 <60%Frequent

Management

General principles:

  • Stepwise therapy based on severity

  • Reduce triggers and manage comorbidities (GERD, obesity, rhinosinusitis)

  • Frequent monitoring: PFTs every 3–6 months initially, then 1–2 years once stable

  • Provide asthma action plan

Stepwise Pharmacotherapy (≥12 years):

  • Relievers: SABA (albuterol), ICS/formoterol, SAMA (ipratropium)

  • Maintenance: ICS, ICS/LABA, LAMA (tiotropium), leukotriene antagonists

  • Severe/refractory asthma: Biologics (anti-IgE, anti-IL-4R, anti-IL-5/IL-5R), low-dose oral glucocorticoids

Special considerations:

  • Pregnancy: Same stepwise therapy; monitor monthly

  • Children <5 years: Use glucocorticoid-containing regimens; nebulizers if needed

  • Perioperative: Continue ICS, give hydrocortisone if at risk of adrenal suppression

Adjunctive therapy:

  • Reduce trigger exposure, consider allergen immunotherapy

  • Vaccinations (flu, COVID-19, pneumococcal)

  • Lifestyle: diet, exercise, smoking cessation, stress management

Key Points

  • Asthma is heterogeneous: Multiple phenotypes exist, with variable triggers and ICS responsiveness.

  • Diagnosis requires both symptoms and variable airflow: Biomarkers can support diagnosis when PFTs are inconclusive.

  • Management is stepwise and individualized: Focus on reducing inflammation, preventing exacerbations, and controlling comorbidities.

  • Severe or uncontrolled asthma may need specialist care and biologic therapy.

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