Nine years of patch testing with isocyanates in a clinic of occupational dermatology

BackgroundIsocyanates are used as starting materials of polyurethane (PU) products. They are relatively important occupational skin sensitizers.ObjectivesTo analyse results of a large isocyanate patch test series of 19 isocyanate test substances and 4,4 '-diaminodiphenylmethane (MDA), a marker of 4,4 '-diphenylmethane diisocyanate (MDI) hypersensitivity.MethodsTest files were screened for positive reactions in the isocyanate series. Patients with positive reactions were analysed for occupation, exposure and diagnosis.ResultsIn 2010-2019, 53 patients had positive reactions in the series (16% of 338 patients tested). MDA, the well-established screening substance for MDI allergy, was positive in 30 patients, an in-house monomeric MDI test substance in 23 patients and 3 different polymeric MDI test substances in 19-21 patients. We diagnosed 16 cases of occupational allergic contact dermatitis (OACD) from MDI including 3 pipe reliners. Hexamethylene-1,6-diisocyanate (HDI) oligomers in paint hardeners caused 5 cases of OACD, more cases than 2,4-toluene diisocyanate (TDI; n = 3) and isophorone diisocyanate (IPDI; n = 1) put together.ConclusionsIn contrast to previous studies, polymeric MDI test substances were not superior to a monomeric MDI. Pipe reliners may get sensitised not only by epoxy products and acrylates but also by MDI in hardeners of PU pipe coatings. HDI oligomers were the second most important causes of OACD after MDI. In contrast to previous studies, polymeric MDI patch test substances were not superior to a monomeric MDI. Pipe reliners may get sensitised by MDI in hardeners of polyurethane pipe coatings. HDI oligomers were the second most important causes of occupational allergic contact dermatitis after MDI.