Allergy in the Lung

Question 1

Define intolerance and define allergy [2]

Answer 1

1. Intolerance is the inability to cope with normally acceptable conditions/exposures
2. An allergy is an immune system mediated intolerance

Question 2

What are the stages of an allergic reaction? [5]

Answer 2

1. Trigger
2. Recognition
   
   • after the first exposure
3. Memory
   
   • lifelong
4. Response
   
   • Immediate (type 1 hypersensitivity)
     
     • IgE and mast cell (histamine) mediated
   • Delayed (reactive T cells)

Question 3

What does chronic allergy lead to? [1]

Answer 3

tissue remodelling

Question 4

What is rhinitis? [1]

Answer 4

inflammation of the mucosal lining of the nose

Question 5

Describe the clinical features/pathogenesis of allergy in the upper/extra-thoracic airways and how do you investigate it? [5]

Answer 5

1. Upper/extra-thoracic airways (e.g. trachea) are not susceptible to intrathoracic pressure due to tracheal rings holding the airway steady
2. Extra-thoracic disease that can cause inflammation of the upper airways:
   
   • laryngeal oedema
   • stridor
3. Investigate with flow volume loops

Question 6

Describe the clinical features/pathogenesis of allergy bronchial diseases and how do you investigate it? [5]

Answer 6

1. Bronchi are medium to small airways with flaccid walls which are susceptible to intrathoracic pressure
2. Bronchial diseases causes:
   
   • Narrowing during the expiratory phase
     
     • leading to wheeze
   • Impaired muco-ciliary clearance
     
     • leading to excess sputum production
3. Investigate with flow volume loops

Question 7

Describe the pathogenesis of asthma [5]

Answer 7

1. The airway allergy drives eosinophilic inflammation
2. Inflammation causes the epithelial cells to die
   
   • their death drives further inflammation and therefore more death and this cycle continues.
3. The eosinophils that show up to the epithelium release cytokines and mediators - REMEMBER IL5 & 13
4. TNF-α, TGFb and VEGF cause airway remodelling:
   
   • fibrosis, angiogenesis, epithelial cell damage, smooth muscle hypertrophy

Question 8

Describe the 3 overlapping types of asthma and the clinical features of each [17]

Answer 8

1. Physiological: Reversible/variable airflow obstruction
   
   • Yellow mucous
   • Repair pathways
   • Non-elastic airways
   • Increased responsiveness
   • Increased sensitivity
2. Pathological: Airway inflammation/allergy
   
   • Inflammation
   • Scabby epithelium
   • Thickened BM
   • Thickened smooth muscle
   • Mast cells in the smooth muscle
3. Clinical: Wheeze due to triggers: cold, exercise, cats, aspirin
   
   • Cough
   • Wheeze
   • Hyperreactivity
   • Hypersensitivity

Question 9

What are the typical triggers of asthma? [4]

Answer 9

1. Exercise
2. Chemical — aspirin (hyperreactivity)
3. Cats (allergy)
4. Diurnal — nocturnal awakening

Question 10

What are the treatment options for asthma/allergic reaction? [7]

Answer 10

1. Bronchodilators
   
   • SABA
2. Corticosteroids
   
   • reduces inflammation
3. Anti-leukotriene receptors
4. Anti IgE
   
   • ​​targets type I hypersensitivity
5. Immunotherapy
6. Biological therapies
   
   • ​targets IL5 & 8
7. Thermoplasty
   
   • debulks smooth muscle

Question 11

Describe the pathogenesis of an allergic disease in the lung parenchyma [4]

Answer 11

1. Type III hypersensitivity — immune complex disease
2. Antigen presents at the alveoli while breathing in, the antibody (made after first exposure) will bind to the antigen and cause an immunocomplex to form.
3. This will eventually block up the capillary and cause minor infarctions of the lungs, acute inflammation and influx of neutrophils.
4. This causes the build-up of fluid in the alveoli — this is shown in a CXR as consolidation

Question 12

Describe the typical presentation of allergic disease in the lung parenchyma [11]

Answer 12

1. Acute illness:
   
   • occurs 4-6 hours after exposure
   • may last several days
2. Signs & Symptoms:
   
   • wheeze,
   • cough,
   • fever,
   • chills,
   • headache,
   • myalgia,
   • malaise,
   • fatigue

Question 13

What are the clinical consequences of an allergic disease in the lung parenchyma? [4]

Answer 13

1. Thickening of the septae
2. Filling of the alveoli with fluid
3. Loss of O₂ — hypoxaemia
   
   • (but CO₂ is normal - type 1 resp failure)
4. In CXR — air space shadowing = consolidation

Question 14

Describe the complications of chronic exposure to allergens in the lung parenchyma [2]

Answer 14

1. Fibrosis
   
   • interstitial scarring from chronic tissue remodelling/repair pathway
     
     • (the lung isn’t given enough time to properly heal before being exposed again)
   • functional tissue is replaced with scar tissue
2. Emphysema
   
   • due to interstitial destruction from neutrophilic enzyme release

Question 15

Describe the pathogenesis of extrinsic allergic alveolitis [5]

Answer 15

1. Immediately: acute illness due to type III reaction
   
   • serum sickness/immune complex disease
2. After a few days/weeks: subacute
   
   • Type IV T cell mediated reaction
3. Then over a longer period of time, you get pulmonary fibrosis and emphysema — chronic inflammation

Question 16

What is the treatment of extrinsic allergic alveolitis? [3]

Answer 16

1. Allergy - avoid trigger
2. Inflammation - corticosteroids
3. O₂ supplementation