Extrinsic allergic alveolitis Flashcards
Define:
Interstitial inflammatory disease of distal gas exchanging parts of the lungs caused by inhaled organic dusts.
A.K.A - hypersensitivity pneumonitis
Aetiology/risk factors:
Sensitised individuals - repeated inhalation of allergen leads to a hypersensitivity reaction
Alveoli are infiltrated with acute inflammatory cells
Removal of the allergen leads to good prognosis
Chronic exposure leads to granulomas and obliterative bronchioloitis
What are types of EAA:
Farmers lungs- due to mouldy hay
Pigeon Fancier’s lung - blood on feathers
Malt workers lung - Aspergillus Clavatus found on barley and maltings
Bagassosis or sugar worker’s lung (Thermoactinomyces sacchari)
Epidemiology:
Uncommon
2% of occupational lung diseases
50% of reported cases affect farmers
Geographical variation
Symptoms:
Acute usually present 4-12 hours after exposure:
Reversible episodes of:
- Dyspnoea
- Dry cough
- Malaise
- Fever
- Myalgia (pain in muscles or a group of muscles)
May have wheeze and a productive cough
Chronic:
- Slowly increasing breathlessness
- Decreased exercise tolerance
- Weight loss
- history of previous episodes
Signs:
Acute:
- rapid shallow breathing
- pyrexia
- inspiratory crackles
Chronic
- Fine inspiratory crackles
- clubbing (rare)
Investigations:
Bloods:
-FBC (neutrophilia and lymphopenia), ESR
ABG:
-Low PCO2 and PO2
Sereology:
-IgG test for fungal and avian antigens
CXR
- often normal
- acutely may see fibrosis + hilar lymphadenopathy
- Chronically may see upper zone fibrosis and honeycomb lung
High resolution CT thorax:
- Early changes detected
- ground glass shadowing
- nodules
- extensive fibrosis
pulmonary function tests:
- Decreased FEV1 and FVC
- normal or increased FEV1/FVC ratio
- decreased TLC
- decreased gas exchange
Bronchoalveolar levage
-increased mast cells and lymphocytes
Lung biopsy in some cases
