What is eosinophilic asthma?

Eosinophilic Asthma: Definition and Characteristics

Eosinophilic asthma is a distinct asthma phenotype characterized by elevated eosinophil counts in the airways (>3% in sputum), which contributes to airway inflammation, often presents as late-onset disease, and may be associated with more severe symptoms and potential steroid refractoriness. 1

Key Diagnostic Features

• Gold standard diagnostic criteria:

  • Sputum eosinophil count >3% (indicating significant eosinophilic airway inflammation) 1
  • Elevated blood eosinophil counts (typically >300 cells/μL) 1
  • Elevated fractional exhaled nitric oxide (FeNO) as a non-invasive biomarker 1

• Clinical characteristics:

  • Often associated with late-onset asthma (adult-onset)
  • More severe disease presentation
  • Potential steroid refractoriness
  • May occur with or without atopy (allergic sensitization) 1
  • Frequent exacerbations despite standard therapy

Pathophysiology

• Immune response: Involves a complex network of interconnected pathways from both adaptive and innate immune systems 2

• Key inflammatory mediator: Interleukin-5 (IL-5) plays a central role in:

  • Eosinophil differentiation
  • Eosinophil activation
  • Eosinophil survival 2

• Mast cell localization: Unlike classic allergic asthma where mast cells infiltrate airway smooth muscle, in eosinophilic bronchitis, mast cells localize primarily in the epithelium 1, 3

• Inflammatory effects: Eosinophils release mediators and cytokines that contribute to:

  • Severe airway inflammation
  • Tissue damage
  • Airway remodeling 4

Distinction from Other Asthma Types

• Allergic asthma: Typically early-onset, IgE-mediated, and responsive to allergen avoidance

• Non-eosinophilic asthma: Characterized by neutrophilic or paucigranulocytic inflammation

• Nonasthmatic eosinophilic bronchitis: Similar eosinophilic inflammation but without:

  • Variable airflow limitation
  • Airway hyperresponsiveness 3, 1

Treatment Approach

• First-line therapy: Inhaled corticosteroids (ICS) 1

  • Often requires higher doses than allergic asthma

• Add-on therapies:

  • Long-acting beta-agonists (LABA) with ICS
  • For severe cases: Biologic therapies targeting the IL-5 pathway:
    • Mepolizumab (anti-IL-5) 5
    • Reslizumab (anti-IL-5) 6
    • Benralizumab (anti-IL-5 receptor) 2

• Monitoring:

  • Symptom control
  • Lung function (spirometry)
  • Exacerbation frequency
  • Biomarkers (blood eosinophils, sputum eosinophils, FeNO) 1

Clinical Implications

• Management strategies aimed at normalizing sputum eosinophil counts have been associated with up to 60% reduction in severe asthma exacerbations 1

• Biologic therapies should be considered in patients with:

  • Severe uncontrolled asthma
  • Poor response to standard therapy
  • Requirement for high-dose ICS or frequent oral corticosteroids 1

• Important to note that biologic therapies do not treat acute symptoms or exacerbations 5, 6

Understanding the distinct features of eosinophilic asthma is crucial for appropriate diagnosis and targeted treatment, which can significantly improve outcomes for patients with this specific asthma phenotype.