pneumonitis
Summary
General term for inflammation of lung parenchyma, usually non-infectious. Common causes include hypersensitivity (e.g., farmer's lung), drug toxicity (amiodarone, bleomycin, methotrexate), radiation, and aspiration of chemical irritants.
Detail
While 'pneumonia' is typically reserved for infectious lung inflammation, 'pneumonitis' is used for non-infectious or hypersensitivity-mediated inflammation. Hypersensitivity pneumonitis is a mixed type III/IV reaction to inhaled organic antigens (thermophilic actinomycetes in farmer's lung, avian proteins in bird-fancier's lung) causing dyspnea, cough, and ground-glass infiltrates; chronic exposure leads to upper-lobe fibrosis with noncaseating granulomas. Drug-induced pneumonitis is classic for amiodarone, bleomycin, busulfan, methotrexate, and immune-checkpoint inhibitors. Aspiration pneumonitis (Mendelson syndrome) is chemical injury from gastric acid, distinct from aspiration pneumonia. Treatment is removal of exposure and corticosteroids.
Sources
- First Aid for USMLE Step 1 2024
- Robbins Basic Pathology 10th ed
- Pathoma
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