Follow-up study of 232 patients with occupational asthma caused by western red cedar ( Thuja plicata)

A total of 232 patients with red cedar asthma diagnosed by inhalation provocation tests were observed an average of 4 years after the initial diagnosis. The status during the follow-up examination was as follows: 96 patients continued to work with red cedar, and 136 left the industry and had no further exposure to red cedar in their jobs or hobbies. Of the 136 patients who left the industry, only 55 (40.4%) recovered completely, whereas the remaining 81 (59.6%) continued to experience attacks of asthma of varying severity. The initial pulmonary function tests were significantly higher among the asymptomatic group compared to the symptomatic group (FEV 1 99.3 ± 2.7% versus 90.5 ± 2.2% predicted, respectively). Methacholine PC 20 during the initial examination was higher among the asymptomatic group than in the symptomatic group (1.46 ± 3.96 mg/ml versus 0.77 ± 4.52 mg/ml, respectively). These findings indicate that the patients in the asymptomatic group were diagnosed at an earlier stage of the disease. This observation was confirmed by the significantly shorter duration of symptoms before diagnosis among the asymptomatic patients compared to the symptomatic patients (1.6 ± 1.9 versus 2.6 ± 4.3 years). Race, smoking status, immediate skin reactivity, and presence of plicatic acid-specific IgE antibodies did not influence the outcome of these patients. Of the 96 patients who continued to work with red cedar, 47 were exposed daily, whereas 41 were exposed intermittently. They all had respiratory symptoms and required medications. Both groups of patients demonstrated a reduction in FEV 1 and FVC on follow-up examination and an increase in nonspecific bronchial responsiveness, although the differences failed to reach the level of statistical significance. This study emphasizes the importance of early diagnosis and early removal from exposure in patients with occupational asthma. The removal from exposure should be complete because partial removal did not prevent the deterioration of function of those who were continuously exposed.