Use of mannitol challenge for assessing workers with occupational asthma
Published Online: October 24, 2011
Airway hyperresponsiveness is a state characterized by easily triggered bronchospasm (twitchiness of the airways). Along with airway inflammation, airway hyperresponsiveness is a hallmark of asthma. Methacholine challenge is a test that allows the assessment of airway responsiveness in asthma by acting directly on the airway smooth muscle and inducing its contraction. Mannitol challenge is another test used to measure airway responsiveness but does not act directly on the airway smooth muscle (indirect challenge). Although both tests measure airway hyperresponisveness they may not provide identical information. Occupational asthma is a type of asthma caused by a specific agent at the workplace to which the workers become sensitized. Even if a specific substance has been identified as the cause for the onset of OA, the removal from this substance does not, in the vast majority of subjects, induce a remission of the disease. Assessing the persisting activity of the disease and the impairment/disability of the workers with occupational asthma is in important for rehabilitation and compensation purposes.
In a Letter to the Editor in The Journal of Allergy and Clinical Immunology (JACI), Lemiere et al hypothesized that the activity of a persisting occupational asthma may be more accurately assessed by a mannitol bronchial provocation test (BPT) than by a methacholine BPT. The authors compared the airway hyperresponsiveness assessed by methacholine and by mannitol BPTs in workers with previously diagnosed OA.
The researchers assessed 30 subjects with a diagnosis of OA made between 2000 and 2008 who had been removed from exposure since their diagnosis. Those subjects were assessed on two separate visits scheduled two to seven days apart, during which a mannitol and a methacholine BPT were performed. Airway inflammation was also measured by analyzing sputum cell counts. The asthma control and the fraction of exhaled nitric oxide (another way to assess airway inflammation) were also assessed at each visit.
The researchers found that although mannitol BPT was positive in the minority of subjects (30%), those with a positive mannitol BPT had a more active disease in terms of greater airflow limitation, more airway inflammation, and higher exhaled nitric oxide levels compared to the subjects with a negative mannitol BPT. The authors’ findings suggest that mannitol BPT may be more relevant than methacholine BPT for assessing the impairment/disability of subjects with a previous diagnosis of OA.
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.