Toluene diisocyanate induced asthma: outcome according to persistence or cessation of exposure.

Sir,-We read with interest the article by Pisati et al (1993;50:60-4) regarding outcome according to persistence or cessation of exposure to toluene diisocyanate. In a recent analysis of asthma compensation claims in Ontario, we have also found (data submitted for publication), as have some of the other reports referenced by Pisati et al, that duration of symptoms before leaving exposure and initial pulmonary function measures were important predictors of outcome. In explaining the poor state of group A who were still exposed, is it possible that Pisati et al could further sort out the role of continued exposure to toluene diisocyanate v the initial circumstances such as long duration of exposure and long duration of symptoms before diagnosis? In particular, among the nonimproved subjects within group B (subgroup III) who were no longer exposed, the baseline PDI5 of 424 was similar to that among group A who were still exposed (425). Moreover, as the authors point out, subgroup III had a long mean duration of exposure (15-9 years), and mean duration of symptoms before diagnosis (5 4 years), again similar to those among group A (25 and 6-3 years, respectively). The baseline FEV, was somewhat lower, however, among group A than subgroup III (86-8% v 94%). The authors indicated that it was not possible to analyse group A in this way (because no subjects recovered). Whereas removal from exposure is probably the only effective way of preventing deterioration, it would be of interest if the authors could look at subgroups or examine the relative importance of duration of exposure and symptoms before diagnosis v persistent exposure as predictors of outcome in comparing group A and subgroup III, as they were similar at baseline. GARY M LISS Ontanro Ministry of Labour SUSAN M TARLO The Gage Research Institute, Toronto, Ontanro, Canada