Isocyanate-induced occupational asthma: immunologic and challenge studies.

Abstract

Background: Isocyanate is the most significant cause of occupational asthma in this country. The mechanism of isocyanate induced bronchoconstriction is unclear. Subjects and Method: To observe its immunologic and clinical findings, we performed methacholine bronchial challenge test (MBCT), toluene diisocyanate (TDI)-bronchoprovocation test (BPT) and RAST to TDI-, diphenylmethane diisocyanate (MDI)-, and hexamethylene diisocyanate (HDI)-human serum albumin (HSA) conjugate in 22 isocyanate-sensitive asthmatic workers. Results: BPT revealed early (11), dual (5), and late only (6) asthmatic responses. Their latent period ranged from 3 to 120 months (mean:45.9 months). Three cases (13.6%)showed a negative response on initial MBCT, but following MBeT performed 24 hours after TDI-BPT revealed the development of airway hyperresponsivenss. Twelve (54.5%) workers had increased specific IgE to TDI-HSA, seven (31.8%) had to MDI-HSA, and nine (40.9%) had to HDI-HSA conjugate. The prevalence of specific IgE was not associated with latent period, type of asthmatic responses, smoking, and atopic status. After 3 months' avoidance from workplace, airway hyperresponsiveness was improved in 10 (38.3%), among 12 followed cases. Conclusion: It is suggested that isocyanate can induce IgE-mediated bronchoconstriction in 59.1% of isocyanate-sensitive asthmatic workers. Isocyanate-induced asthma can occur even though MBeT showed a negative result, and measurement of the changes of airway hyperresponsivenss after isocyanate-BPT could be helpful to diagnose isocyanate-sensitive asthma.