Isocyanate-induced asthma: results of inhalation tests with TDI, MDI and methacholine.

We performed diisocyanate inhalation tests (maximal concentration, 20 ppb; exposure time, 1-2 h) using toluene diisocyanate (TDI, n = 15) and diphenylmethane diisocyanate (MDI, n = 7) as well as methacholine challenges in 19 workers who had a clinical history of TDI/MDI-induced asthma. Additionally we tested volunteers who had no previous contact with diisocyanates: 10 healthy individuals with a negative methacholine test and 14 patients with asthma and a positive methacholine test were exposed to TDI. In all, 1 of the normal volunteers and 3 of the patients with asthma unrelated to diisocyanates showed a positive airway reaction to TDI, and 13 of the 19 diisocyanate workers displayed a positive result in the TDI/MDI inhalation test; however, only 6 of these 13 individuals reacted to methacholine. Furthermore, 3 of the 6 patients with a negative TDI/MDI challenge test demonstrated a significant response to methacholine. We conclude that bronchial hyperreactivity as evaluated by the methacholine challenge test is not closely related to isocyanate-induced bronchoconstriction and, therefore, the metacholine challenge is only of limited diagnostic value in patients with suspected isocyanate-induced asthma.