The objective of this project was to assess both the outcome for patients diagnosed with proven isocyanate-induced occupational asthma (IIOA) by specific inhalation challenge (SIC) and the functional impairment, 2 years after cessation of exposure to isocyanates, using the compensation insurance scale proposed in the province of Quebec.
We used a retrospective cohort of 233 patients diagnosed in the province of Quebec between 1985 and 2002 and randomly chose 105 of those patients. We kept 89 subjects with complete data at T0 (the time of diagnosis) and 79 were reevaluated at T2, approximately 2 years after their removal from exposure, for final impairment-disability assessment. At each evaluation (T0 and T2), a clinical examination and lung function tests, including spirometry and methacholine challenge, were performed.
At T2, 79 of 89 patients were reassessed (89%). The remaining patients were lost to follow up (8) or too unstable to be reassessed for final impairment-disability settlement (2). No statistical difference was observed for spirometry data and antiasthmatic medication use between T0 and T2 (P = 0.11). At T2, 73% of patients were still using short-acting beta2 agonists and 39% inhaled glucocorticoids. A forced expiratory volume in 1 second variation of +/-10% from T0 to T2 occurred in 31 subjects (40%). Forced expiratory volume in 1 second worsened in 14 (18%), remained significantly unchanged in 51 (64%), and improved in 14 (18%). Nonspecific bronchial hyperresponsiveness (BHR) improved in significantly in 19 (24%); the others remained unchanged. Both were not associated with smoking status (P > 0.05). Nonspecific BHR was normalized in nine of 79 (11%) patients. Clinical remission occurred in only four (5%) subjects. The mean impairment-disability score was 21% +/- 13% at 2 years according to the scale used by the Workers' Compensation Board.
These results show the generally poor medical outcome of IIOA and suggest the importance of early detection and withdrawal of the workers from exposure to isocyanates. They also emphasize the need for medical surveillance program and adequate treatment of patients with IIOA.