Hypersensitivity Pneumonitis

Question 1

Defintion

Answer 1

Type 3 hypersensitivity reaction where immune complexes are deposited (Ab-Ag) in the basement membrane of pulmonary blood vessels and causes immune hyper-response

Question 2

Triggers

Answer 2

Farmer’s lung (MC)
- mouldy hay
Pigeon farmers lung
- bird droppings
Maltworkers lung
- aspergillus from mouldy barley
Cheeseworkers lung
Humidifier fever

Question 3

Acute Symptoms

Answer 3

Fever
SOB
Cough
Chest tightness
Headache
* typically resolves 12 hours to several days after cessation of exposure *

Question 4

Subacute symptoms

Answer 4

Productive cough
Dyspnoea
Fatigue
Weight loss
Mild hypoxia
* resolves weeks to months after cessation of exposure *

Question 5

Chronic symptoms

Answer 5

Insidious onset cough
Progressive dyspnoea
Fatigue
Weight loss
Clubbing
Tachypnoea
Inspiratory crackers (lower lung fields)
Emphysematous component
May be irreversible even after antigen removed

Question 6

Diagnosis

Answer 6

CXR:
- subacute = micro nodular opacification in middle, lower lung zones
- chronic = progressive fibrotic changes, loss of lung volume (esp upper lobes)
High-res CT:
- subacute = ground glass opacification, focal air trapping, mild fibrosis
- chronic = interstitial inflammation, alveolar destruction, dense fibrosis, emphysema symptoms, sub-pleural honeycombing
Bronchoscopy/ broncho-alveolar lavage:
- marked lymphocytosis = Increased IgG, IgA, IgM

Question 7

Treatment

Answer 7

Remove allergen
Chronic = steroids/ immunosuppression
Last resort = lung transplant