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Eosinophilic Asthma: Causes, Symptoms, Diagnosis, Treatment, and Prognosis

Eosinophilic asthma is a chronic inflammatory asthma subtype defined by elevated eosinophils—specialized white blood cells—in the airways, blood, or sputum. It accounts for ~40–50% of severe asthma and has distinct pathophysiology, biomarkers, and targeted treatments.

Pathophysiology: The Eosinophilic Cascade

Type 2 inflammation drives the process: epithelial alarmins (IL-33, TSLP, IL-25) → activate ILC2s and Th2 cells → produce IL-4, IL-5, IL-13 → IL-5 stimulates eosinophil production/maturation in bone marrow → eosinophils migrate to airways (CCR3/eotaxin) → release toxic granules (MBP, ECP, EPO) → epithelial damage, bronchoconstriction, mucus hypersecretion, airway remodeling.

Clinical Presentation

  • Wheezing, coughing (often nocturnal), dyspnea, chest tightness
  • Sleep disturbance, exercise limitation, fatigue
  • Often later onset (30s–50s), may be non-atopic
  • Frequent exacerbations requiring oral corticosteroids
  • Nasal polyps, chronic sinusitis commonly coexist

Diagnosis: Confirming the Phenotype

  • Blood eosinophils: ≥150 cells/µL (some guidelines ≥300 for biologic eligibility). Repeatable.
  • Sputum eosinophils: ≥2–3% (gold standard but less accessible).
  • FeNO (Fractional Exhaled Nitric Oxide): ≥25–50 ppb supports Type 2 inflammation.
  • Serum IgE, periostin: Adjunctive biomarkers.
  • Clinical context: Exclude parasitic infection, EGPA, ABPA, drug reaction (DRESS), hypereosinophilic syndrome.

Treatment: Stepped and Targeted

  1. ICS/LABA (Foundation): Medium-high dose. Adherence critical.
  2. Leukotriene Modifiers: Montelukast—adjunct, especially if aspirin-exacerbated respiratory disease (AERD).
  3. LAMA (Tiotropium): Add-on for persistent obstruction.
  4. Oral Corticosteroids: Bursts for exacerbations; maintenance avoided if possible (toxicity).
  5. Biologics (Game-Changers for Severe Eos Asthma):
    • Anti-IL-5: Mepolizumab (SC q4wk), Reslizumab (IV q4wk)
    • Anti-IL-5R: Benralizumab (SC q8wk after loading) — depletes eosinophils via ADCC
    • Anti-IL-4Rα: Dupilumab (SC q2wk) — blocks IL-4/IL-13, broader Type 2
    • Anti-TSLP: Tezepelumab (SC q4wk) — upstream epithelial alarmin
  6. Bronchial Thermoplasty: For selected severe asthma uncontrolled by biologics.

Prognosis and Prevention

  • Generally good with phenotype-appropriate treatment. Biologics reduce exacerbations 50–70%, improve FEV1, quality of life, allow OCS sparing.
  • Airway remodeling (subepithelial fibrosis, smooth muscle hypertrophy) may be partially reversible with early biologic intervention.
  • Prevention: allergen/irritant avoidance, annual flu/COVID/pneumococcal vaccines, regular exercise, healthy weight, sleep hygiene, stress management, smoking cessation (absolute).

Eosinophilic asthma is no longer a therapeutic dead end. With biomarker-guided biologic therapy, most patients achieve control previously thought impossible. The key: accurate phenotyping, early specialist referral, and shared decision-making.

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