Occupational Asthma Reference

Malo J-L, 'Daily pattern' of an asthmatic reaction due to isocyanates, Allergy, 2004;59:234-235,

Keywords: challenge, HDI, pattern of reaction, reproducibility

Known Authors

Jean-Luc Malo, Hôpital de Sacré Coeur, Montreal, Quebec, Canada Jean-Luc Malo

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We describe the case of a subject who developed changes in forced expiratory volume (FEV1) that were significant when examined from day to day ('daily pattern' of reaction) but were not significant when values up to 7 or 8 h after ending challenge were considered.

A 44-year-old car painter developed work-related respiratory symptoms approximately 1 year before being examined. He underwent specific inhalation challenges 3 months after leaving work. Table 1 summarizes the results of specific challenges to hexamethylene diisocyanate (HDI); these were carried out in a small cubicle by using a closed-circuit apparatus and a realistic approach. On 23 April 2003, the day-to-day % change in FEV1 was significant (-23%) whereas at hourly changes it was not (-15.1%). On the same day, PC20 fell significantly to 19 mg/ml, although remaining within normal values (PC20 > 16 mg/ml). There was also a significant increase in sputum eosinophils. Six days after stopping the challenge, on day 30 April 2003, baseline FEV1 improved and sputum eosinophils were back to 0%. After exposure to HDI on 01/05/03, there was a significant (-21.1%) hourly change accompanied by a fall in PC20 to an abnormal range and an increase in sputum eosinophils to 24%.

This case report illustrates that, while changes in FEV1 documented 7–8 h after challenge did not reach significance, the changes in FEV1 from one day to the next can do so. This illustrates a 'daily pattern' of reaction which has so far been described with serial monitoring of peak expiratory flow rates. Interestingly, PC20 fell significantly and sputum eosinophils increased before significant hourly changes could be demonstrated, pointing out that these tools are at times more sensitive than hourly changes in FEV1 for documenting a reaction. It is interesting to note that discontinuation of exposure to the causal agent for almost 1 week resulted in the documentation of an 'hourly pattern.' We therefore think that it is relevant to assess FEV1 24 h after stopping exposure in cases where borderline changes in FEV1 are obtained after 7–8 h.

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