Occupational asthma and rhinitis due to Western red cedar (Thuja plicata).

SUMMARy _ Twenty-two woodworkers presenting with respiratory symptoms after exposure to the dust of western red cedar were studied. Eighteen of them had bronchial reactions to the inhalation of red cedar extract. They presented with a characteristic clinical picture. After a period of intensive exposure to red cedar, they developed nocturnal attacks of cough and asthma. Later, symptoms occurred earlier during the day if they continued to work with this wood. Twelve of them also had rhinitis. They improved during weekends and holidays. Most recovered within 6 months of cessation of exposure. The inhalation provocation test was the only method of confirming the. diagnosis. An immediate asthmatic reaction was induced in 4, a late asthmatic reaction in 8, and "dual" reactions in the remaining 6 patients. Skin tests with extract of this wood produced an immediate reaction in only 3 patients. Precipitin studies failed to detect the presence of antibodies in the patients' sera against the extract of this wood. The 4 patients who did not react to red cedar extract on inhalation presented with a different clinical picture. They did not recover on cessation of exposure. In provocation tests, plicatic acid, a major fraction in the red cedar extract, produced bronchial reactions similar to those produced by the whole extract. Plicatic acid .is probably the compound in the red cedar that causes the respiratory symptoms. The p.attern of inhalation reaction suggested an allergic basis.