Hypersensitivity pneumonitis Flashcards
What is it
Type of Interstitial Lung Disease (ILD) - distinct cellular infiltrates and extracellular matrix deposition in lung distal to the terminal bronchiole i.e. diseases of the alveolar/capillary interface
What are Interstitial lung diseases
group of lung diseases affecting the lung interstitium (the tissue and space around the air sacs of the lungs)
Epidemiology
Usually adults affected
Aetiology
Caused by an allergic reaction affecting the small airways and alveoli in response to an inhaled antigen (fungal spores or avian proteins) or occasionally following the ingestion of a causative drug
Associated with many jobs and hobbies
What can result from chronic hypersensitivity pneumonitis
Fibrosis
Emphysema
Permanent lung damage
Give example where disease is associated with jobs and hobbies
Farmers lung - exposure of mouldy hay
Bird fanciers lung - exposure to avian proteins in droppings
Cheese-workers lung - exposure of mouldy cheese
Causative organisms of Farmers lung
Micropolyspora faeni Aspergillus umbrosus (fungi)
Risk factors
- Pre-existing lung disease
- Specific occupations including farmers, cattle workers, ventilation system workers, vets and those jobs that involve working with chemicals
- Bird keeping
- Regular use of hot tubs
Pathophysiology
Type 3 hypersensitivity reaction
Allergic response to the inhaled antigen involves both cellular immunity and the deposition of immune complexes, resulting in inflammation through the activation of complement.
These mechanisms attract and activate alveolar and interstitial macrophages so that continued antigenic exposure results in the progressive development of pulmonary fibrosis.
Describe acute phase
the alveoli are infiltrated with acute inflammatory cells
Describe chronic phase
With chronic exposure, granuloma formation and obliterative bronchiolitis
(inflammation of bronchioles) occur
Farmers lung pathophysiology
Fungus in mouldy hay is inhaled
If individual is already sensitised to the organism, a type III immune complex hypersensitivity reaction follows
Clinically there is acute dyspnoea (difficulty breathing) and cough a few hours after inhalation of the antigen
Bronchiolitis is also an early feature
Chronic inflammatory cells are later seen in the interstitium together with non-caveating granulomas
Clinical presentation of acute (4-6 hours post-exposure)
Fever Rigors Myalgia Dry cough Dyspnoea Crackles (no wheeze) Chest-tightness Patients may be mistakenly diagnosed with a chest infection Symptoms related to level of exposure Resolution occurs 24-48hrs following removal of the antigen
Clinical presentation of sub-acute
History or repeated acute attacks
Signs same as acute, symptoms less severe and more gradual onset
Improvement is seen in weeks to months following removal from exposure
Clinical presentation of chronic
Usually no history of preceding acute symptoms
If the source of antigen is removed only partial improvement of symptoms
Cyanosis and clubbing may develop
Weight loss
Increasing dyspnoea
Type 1 respiratory failure
