Extrinsic Asthma


Extrinsic Asthma, Allergic Asthma, T2 Asthma, T2 High Asthma, Th2 Asthma, T Helper Cell Type 2 Asthma, Type 2 Asthma, Atopic Asthma, Eosinophilic Asthma

  • Epidemiology
  1. Much more common in children than adults
  2. Age Onset under 40 years old
  • Pathophysiology
  1. IgE mediated response to allergens
    1. Immediate Allergic Reaction
    2. Late-phase Allergic Reaction
  1. Early Onset Allergic Asthma (Atopic Asthma)
    1. Classic Asthma presentation, allergic sensitization and steroid responsiveness
  2. Late Onset Eosinophilic Asthma
    1. Often steroid refractory, and typically severe from onset with frequent exacerbations
    2. Associated with Staphylococcus aureus enterotoxins
  3. Aspirin Exacerbated Respiratory Disease (Samter's Triad)
    1. Associated with disordered Arachidonic Acid metabolism (cyclooxygenase mediated to inflammatory agents)
    2. Typically severe from onset with frequent exacerbations
    3. Associated with increased urinary LTE4 > 166 pg/mgCr
      1. Divekar (2016) J Allergy Clin Immunol Pract 4(4): 665-70 [PubMed]
  • Causes
  • Triggers
  1. Indoor allergens (perennial allergens)
    1. House Dust mites (most common extrinsic allergen)
    2. Animal Proteins (cat or dog dander)
    3. Mold spores (e.g. Alternaria)
    4. Cockroaches (esp. German Cockroach)
  2. Outdoor allergens (seasonal allergens)
    1. Tree, grass or weed pollens
    2. Mold Spores
  3. Aspirin Exacerbated Respiratory Disease (Samter's Triad)
    1. Aspirin or NSAID sensitivity
    2. Nasal Polyps
    3. Asthma
  • Findings
  • Symptoms and Signs
  • Labs
  • Markers
  1. Eosinophilia
    1. Induced Sputum with >3% Eosinophils
    2. Complete Blood Count with increased Eosinophils
  2. Fractional Excretion of Nitric Oxide (FeNO)
    1. FeNO > 50 ppb in adults (>35 ppb in children) is associated with Eosinophilic airway inflammation
    2. Positive values are associated with steroid responsiveness
  3. Serum Total IgE
  4. Serum Periostin
    1. Elevated in Type 2, Eosinophilic Asthma
  • Management
  1. See Environmental Allergen
  2. See Asthma Management
  3. See Asthma Exacerbation
  4. Consider Immunotherapy for those with persistent Allergic Rhinitis and Asthma
  5. Allergic, refractory Severe Asthma may be treated with Biologic Agents