Restrictive lung disease - Hypersensitivity pneumonitis Flashcards
What is hypersensitivity pneumonitis?
Allergic alveolitis or extrinsic allergic alveolitis
Inflammation of the alveoli within the lung caused by hypersensitivity to inhaled organic dusts. Sufferers are commonly exposed to the dust by their occupation or hobbies.
What is the pathology that occurs in hypersensitivity pneumonitis?
Begins in the centracinar region of the acinus - where the majority of antigens are often deposited. In response to the presence of an antigen/organic matter, there is an infiltration of the small airways and alveolar walls with neutrophils followed by T-lymphocytes and macrophages. This leads to granuloma formation AND chronic inflammation of the interstitium, resulting in the development of soft centriacinar epithelioid granulomas, occasionally containing the undigested antigenic material.
The alveolar walls become thickened due to the chronic inflammation of the interstitium, and granulomas are also present. Due to the combination of type III and type IV hypersensitivity, there is more of a tendency for this disease to lead to pulmonary fibrosis.
What type of hypersensitivity reactions are involved in hypersensitivity pneumonitis?
Type III and IV
Which zone of the lung does hypersensivity pneumonitis most commonly affect?
Upper zones
What are the different types of hypersensitivity pneumonitis?
- Farmer’s lung
- Bird fancier’s lung
- Humidifier fever
- Mushroom workers lung
- Cheese worker’s lung
- Winemaker’s lung
What pathogens are implicated in farmer’s lung?
- Thermophilic acinomycetes
- Fungi - aspergillus
What pathogens are implicated in Bird fancier’s lung?
Proteins present in the blooms and feathers
What pathogen is implicated in Malt worker’s lung?
Aspergillus clavatus
What pathogen is implicated in mushroom worker’s lung?
Thermophilic actinomycetes
What are the symptoms of hypersensitivity pneumonitis acutely?
4-6 hrs post exposure
- Fever/Rigors
- Myalgia
- Dry cough
- Dyspnoea
What are symptoms of chronic hypersensitivity pneumonitis?
- Exertional/Increasing dyspoea
- Weight loss
- Type 1 respiratory failure
- Cor pulmonale
What are signs of hypersensitivity pneumonitis acutely?
Fine inspiratory crackles
NO WHEEZE
What are characteristic of the crackles heard in pulmonary fibrosis?
Short duration crackles, mid to late inspiratory fine crackles
Why do inspiratory crackles occur?
When the negative pressure of inspiration causes airways that have previously collapsed to ‘pop’ open. Once open, there is a sudden equalisation of pressure on either side of the obstruction, resulting in vibrations of the airway wall, creating the sound.
What are signs of chronic hypersensitivity pneumonitis?
- Crackles
- Wheeze
- Cor pulmonale
What might you see on CXR in someone with hypersensitivity pneumonitis?
- Upper-zone mottling/consolidation
- Hilar lymphadenopathy
What might you see on CT in someone with hypersensitivity pneumonitis?
Reticular and nodular changes with ground glass opacity
