Prognostic factors for toluene diisocyanate-induced occupational asthma after removal from exposure

The outcome of isocyanate-induced occupational asthma remains to be further defined. There have been few studies on the role of specific antibodies in prognosis of toluene diisocyanate (TDI) induced occupational asthma. Moreover, to the best of our knowledge, there have been no studies on the improvement pattern of airway hyperresponsiveness (AH). We analysed the prognostic factors that affected the outcome of 35 toluene diisocyanate-induced occupational asthma.

To define clinical and laboratory parameters predicting favourable prognosis for TDI-induced occupational asthma.

After confirmation of bronchial sensitivity by TDI bronchoprovocation test (BPT), 35 patients were recommended to avoid exposure to TDI; they were also given anti-asthmatic medications including inhaled steroids and monitored for 2 years. Seventeen (49%) recovered completely with disappearance of airway hyperresponsiveness (AH) to methacholine during the follow-up period (mean duration: 12 months, range of 3-30 months). Eleven (31%) showed a significant improvement in AH for first year, which improvement stabilized in the next year with mild symptoms. Seven (20%) patients did not show any evidence of improvement in AH and had persistent symptoms. Favourable prognosis was associated with a short duration of asthmatic symptoms before diagnosis (P < 0.05), immediate cessation of exposure after diagnosis (P < 0.05), milder degree of AH at diagnosis (P < 0.05), and the presence of specific IgE antibodies to TDI-human serum albumin conjugate (0.05 < P < 0.1). No association was found with atopic and smoking status, age, exposure duration, or length of latent period (P > 0.05).

These data suggest that early detection of TDI-induced asthma and immediate cessation of exposure are important factors for a favourable prognosis.