Fact-sheet: Extrinsic allergic alveolitis
Updated on 09/17/2021 at 12:16 PM
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Definition
Disease related to the inhalation of organic dust of plant or animal origin, more rarely of chemical origin.
The presence of this organic dust in the terminal respiratory bronchiole and alveoli causes both alveolitis and granulomatous inflammatory bronchiolitis.
Population at risk: farmers, workers in contact with birds.
Clinical features
The following forms are described: - an acute form presenting as a flu-like syndrome with semi-delayed onset (4 to 10 hours) after antigen exposure. - a subacute or progressive form in which symptoms (cough, shortness of breath) are commonly accompanied by deterioration of general condition with weight loss. - a chronic or complicated form corresponding to advanced disease at the stage of chronic respiratory failure due to pulmonary fibrosis or emphysema. Crackles are constant at all stages of the disease. Signs of bronchial hyperreactivity (coughing fits, wheezing...) are frequent.
Laboratory findings
Demonstration of lymphocytic alveolitis on bronchoalveolar lavage (performed during bronchoscopy) is constant but not entirely specific.
Serology is a very useful test, which, when performed with appropriate techniques and an appropriate antigen panel, offers a good sensitivity/specificity trade-off, on the order of 70%.
CT
At the subacute phase:
- Bilateral ground-glass opacities associated with ill-defined centrilobular nodules reflecting the presence of alveolitis and bronchiolitis, with a homogeneous and diffuse distribution.
- Lobular areas of hypoattenuation with hypoperfusion (mosaic perfusion pattern), producing air trapping on expiratory images (resulting from bronchiolar obstruction by fibroblastic tissue plugs), predominating at the bases.
At the chronic phase:
- The extent of the hypodense areas correlates well with the severity of bronchiolar obstruction, which is expressed by increased residual volume.
Management
Antigen avoidance must be complete during the first few months. Systemic corticosteroids accelerate recovery but are reserved for severe forms. Continuation of professional activities among farmers is possible provided that working conditions are adjusted and/or respiratory protective masks are worn.