L'atteinte des voies aériennes distales d'origine environnementale. Pneumopathie d'hypersensibilité et étiologies rares

Hypersensitivity pneumonitis is one of the most frequent causes of distal airways disease. It is associated with inflammation of the bronchioles, predominantly by lymphocytic infiltrates, and with granuloma formation causing bronchial obstruction. This inflammation explains the clinical manifestations and the airways obstruction seen on pulmonary function tests, most often in the distal airways but proximal in almost 20%. CT scan abnormalities reflect the lymphocytic infiltrates and air trapping and, in some cases, the presence of emphysema. Bronchiolitis induced by chronic inhalation of mineral particles or acute inhalation of toxic gases (such as NO2) are other examples of small airways damage due to environmental exposure. The pathophysiological mechanisms are different and bronchiolar damage is either exclusive or predominant. Bronchiolitis induced by tobacco smoke exposure, usually classified as interstitial pneumonitis, is easily diagnosed thanks to broncho-alveolar lavage. Its prognosis is linked to the other consequences of tobacco smoke exposure including respiratory insufficiency. Finally, the complex lung exposure observed in some rare cases (such as the World Trade Center fire or during wars) may lead to a less characteristic pattern of small airways disease.