Serial measurements of peak expiratory flow and responsiveness to methacholine in the diagnosis of aluminium potroom asthma.

BACKGROUND Obstructive airways disease in aluminium potroom workers has been recognised for over 50 years. There is still controversy about whether this is true occupational asthma. METHODS A cross sectional survey of 379 potroom workers identified 26 subjects with symptoms suggestive of occupational asthma. Of these 26, 14 were considered by the plant physician to have occupational asthma and had a measurable PC20 methacholine (provocative concentration causing a 20% fall in FEV1). These 14 were further investigated by serial measurements of peak flow at home and work, symptom diaries, and measurements of methacholine reactivity before and after a three week holiday. RESULTS There was a good correlation between daily symptom scores and minimum peak flow measurements; these showed changes characteristic of occupational asthma in 10 workers, with increased diurnal variation in peak flow and consistent deterioration in relation to work exposure. One further record showed probable occupational asthma and two showed consistent small changes in peak flow related to work exposure more in keeping with an irritant effect. Only one record was inadequate. Methacholine reactivity on a work day was within the normal range in nine of 13 subjects. A doubling of PC20 methacholine occurred in five of nine subjects with occupational asthma in whom repeated estimations were possible. CONCLUSIONS This study confirms the existence of aluminium potroom asthma. The lack of correlation with measurements of non-specific responsiveness suggests that the primary mechanism is one of hypersensitivity, perhaps enhanced by the bronchial irritants also present in the potroom.