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Asthma: Atopic vs. Non-Atopic — Classification, Diagnosis, and Management

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1. Overview and Historical Classification

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2. Atopic (Allergic / Extrinsic) Asthma

Pathophysiology

• IgE-mediated sensitization to environmental allergens (house dust mites, animal dander, cockroach, mold, pollen)
• Hallmark cells: TH2 lymphocytes, mast cells, eosinophils
• Key cytokines: IL-4 (IgE switching), IL-5 (eosinophil recruitment/survival), IL-13 (airway hyperresponsiveness, goblet cell metaplasia, mucus hypersecretion)
• Mast cell degranulation releases histamine, cysteinyl leukotrienes, and prostaglandins → bronchoconstriction
• Eosinophils release major basic protein (damages epithelium), eosinophil cationic protein, and cysteinyl leukotrienes
• Airway remodeling: subepithelial collagen deposition (types III & IV), smooth muscle hypertrophy/hyperplasia, subepithelial angiogenesis

Clinical Features

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3. Non-Atopic (Intrinsic / Non-Allergic) Asthma

Pathophysiology

• NOT IgE-mediated; eosinophilic inflammation driven by innate immunity via Type 2 Innate Lymphoid Cells (ILC2s)
• ILC2s are activated by epithelial alarmins (TSLP, IL-25, IL-33) in response to chronic irritants, pollutants, oxidative agents, fungi, and viruses
• ILC2s produce IL-5 and IL-13 — same downstream effectors as atopic asthma, hence "Type 2-high" despite being non-allergic
• Often associated with chronic rhinosinusitis and nasal polyposis
• Aspirin-exacerbated respiratory disease (AERD): a distinct variant with triad of asthma, nasal polyposis, and aspirin/NSAID sensitivity — characterized by massive leukotriene overproduction

Clinical Features

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4. Extended Phenotype Classification (Modern Framework)

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5. Diagnosis

Step 1: Clinical History

Step 2: Pulmonary Function Testing (Spirometry) — Cornerstone

• Obstructive pattern: reduced FEV1, reduced FEV1/FVC ratio
• Bronchodilator reversibility: ≥12% AND ≥200 mL increase in FEV1 post-bronchodilator — diagnostic
• Peak expiratory flow rate (PEFR), FEV1, and MMEFR all decreased during exacerbation
• Between exacerbations: function may normalize; residual MMEFR depression is common

Step 3: Adjunctive Tests

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6. Differential Diagnosis (Selected)

• COPD (fixed obstruction, smoking history)
• Vocal cord dysfunction / inducible laryngeal obstruction (laryngoscopy diagnostic)
• Heart failure ("cardiac asthma" — rales, not pure wheeze)
• Tracheobronchomalacia
• Endobronchial tumor or foreign body
• Eosinophilic granulomatosis with polyangiitis (Churg-Strauss)

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7. Management — GINA-Aligned Stepwise Protocol

General Goals of Therapy

1. Control daytime and nighttime symptoms
2. No activity limitation
3. Minimize rescue inhaler use
4. Prevent exacerbations and hospitalizations
5. Maintain near-normal lung function (FEV1)

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Medication Classes

Reliever (Rescue) Medications

GINA 2023 update: Regular SABA monotherapy without ICS is no longer recommended due to association with increased asthma mortality. Preferred reliever: as-needed low-dose ICS/formoterol.

Controller Medications

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GINA Stepwise Treatment

STEP 1 (Mild intermittent):
  → Reliever: As-needed low-dose ICS/formoterol
    (Alternative: as-needed SABA + consider low-dose ICS whenever SABA used)

STEP 2 (Mild persistent):
  → Controller: Daily low-dose ICS
  → Reliever: As-needed SABA or low-dose ICS/formoterol
  → Alternative controller: LTRA (montelukast)

STEP 3 (Moderate persistent):
  → Controller: Low-dose ICS/LABA
  → Reliever: As-needed SABA or low-dose ICS/formoterol (if using budesonide/formoterol — MART strategy)
  → Alternative: Medium-dose ICS

STEP 4 (Severe, uncontrolled on Step 3):
  → Controller: Medium-to-high dose ICS/LABA
  → Add: LTRA, tiotropium, or theophylline
  → Consider: Referral for specialist evaluation; assess comorbidities

STEP 5 (Very severe / treatment-resistant):
  → High-dose ICS/LABA + add-on tiotropium
  → Biologic therapy (see below)
  → Oral corticosteroids (OCS) — minimum effective dose; use only when unavoidable

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Biologic Therapies (Step 5 / Severe Asthma)

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Specific Treatment Considerations

Atopic Asthma — Additional Measures

• Allergen avoidance: removal of pets, pest control, impermeable mattress covers (when part of a comprehensive strategy); mold and dust control
• Allergen immunotherapy (subcutaneous or sublingual): indicated in mild–moderate atopic asthma with confirmed sensitization and inadequately controlled rhinitis; not recommended in uncontrolled or severe asthma due to anaphylaxis risk
• First-line biologic: Omalizumab

Non-Atopic (Intrinsic) Asthma — Additional Measures

• Treat associated chronic rhinosinusitis/nasal polyposis aggressively (intranasal corticosteroids; biologics particularly dupilumab)
• AERD: avoid aspirin/NSAIDs; leukotriene modifiers (montelukast, zileuton) are particularly effective; aspirin desensitization in specialist centres
• Poor ICS response — earlier consideration of step-up; biologics preferred
• First-line biologic: Dupilumab (addresses IL-4/IL-13 axis + nasal polyposis), Mepolizumab/Benralizumab for eosinophilic dominant; Tezepelumab for non-type-2

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Acute Exacerbation Management

1. SABA (nebulized or MDI + spacer): salbutamol 2.5–5 mg nebulized q20 min × 3 in first hour
2. Supplemental oxygen: titrate to SpO₂ 93–95%
3. Systemic corticosteroids: prednisolone 40–50 mg PO or IV methylprednisolone; IV for hospitalized patients; IM triamcinolone for adherence issues
4. Ipratropium bromide: add to SABA in severe exacerbations
5. Magnesium sulfate IV: 2 g IV in severe/life-threatening exacerbations not responding to above
6. Heliox, IV theophylline, BiPAP: specialist/ICU-level interventions
7. Mechanical ventilation: last resort; permissive hypercapnia strategy

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Vaccination and Prevention

• Influenza vaccine: annually (strongly recommended)
• Pneumococcal vaccines: all adults with asthma (regardless of age)
• COVID-19 and RSV vaccines: advised

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8. Quick Comparison Summary

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