PREPOLYMERS OF HEXAMETHYLENE DIISOCYANATE AS A CAUSE OF OCCUPATIONAL ASTHMA

Background: Occupational asthma (OA) caused by products that contain h examethylene diisocyanate (HDI) has been ascribed to the highly volati le monomer of HDI. Most two-component paints are now made up primarily of nonvolatile prepolymers of HDI (30% to 60%) with only trace amount s (<0.1%) of the monomer. The respective role of the two chemical form s of HDI in causing OA has never been investigated. Methods: Twenty wo rkers who were consecutively referred for possible OA that resulted fr om exposure to spray paints underwent inhalation challenges on separat e days with pure HDI monomer and the commercial formulation of HDI pre polymers to which they had been exposed at work. Results: Specific inh alation challenges elicited a positive asthmatic reaction in 10 of the 20 subjects. Among these subjects, four had positive bronchial reacti ons (two early, one late, and one dual) to both the monomer and the pr epolymers. Four other subjects had asthmatic reactions (two early, one late, and one dual) after exposure to the prepolymers but not after e xposure to the monomer. The discordance in bronchial response elicited by the monomer and the prepolymers could not be due to differences in the level of baseline nonspecific bronchial reactivity or in HDI conc entrations during the tests. One subject showed an atypical progressiv e reaction after exposure to the monomer but not after exposure to the prepolymer. In this case, the discordant response could be explained by differences in HDI concentration. Conclusion: These observations sh ow that, although they are nonvolatile, the prepolymers of HDI can ind uce OA and that asthmatic reactions as a result of exposure to prepoly mers but not the monomer is not a rare occurrence.