[Occupational asthma: an experimental asthma. Apropos of isocyanate-induced asthma]

Isocyanate-induced occupational asthma is a model of experimental asthma related to the environment. Many of its features are identical with those of allergic asthma by sensitization to air-borne allergens. Exposure to isocyanate before the first symptoms of asthma varies from a few weeks to several years. The prevalence of isocyanate-induced asthma has been estimated at 5 to 25%. Atopy is found in less than 30% of the cases. A significant increase of HRBNS can be demonstrated in most patients, but it may be absent. It may also fluctuate with the working periods or after a bronchial provocation test with isocyanate. Elimination of this compound reduces the HRBNS level in only one quarter of the cases. Delayed or biphasic reactions are frequent: 30 to 60% depending of the authors. An early diagnosis followed by total elimination may result in complete cure, but more than 50% of the patients remain symptomatic and with HRBNS. An IgE-dependent mechanism can be demonstrated in about 20% of the cases. The course of isocyanate-induced asthma is interesting in that the same phenomena are probably observed in chronic asthma resulting from repeated exposures to environmental allergens.