Eosinophilic bronchitis ‘does not respond to bronchial challenge’
MedWire News: The airways of patients with eosinophilic bronchitis (EB) do not respond to direct or indirect bronchial challenge, study results show.
The findings highlight a significant physiological difference between asthma and EB, and “provide further evidence that airway inflammation and airway hyper-responsiveness are dissociated,” say Peter Bradding (University of Leicester, UK) and team.
Writing in the journal Respirology, they explain: “EB shares many pathological features with asthma. However, patients with EB do not develop the characteristic physiological abnormalities of asthma: variable airflow obstruction and bronchial hyper-responsiveness (BHR) to a direct bronchial challenge with methacholine.”
They add: “Indirect bronchial challenges with adenosine monophosphate (AMP) and mannitol are dependent on the presence of airway inflammation, and positive in 10% of asthmatic subjects who have a negative response to methacholine.”
To investigate whether the airways of patients with EB respond to indirect challenge with AMP and mannitol, the researchers enrolled eight patients with the disorder, 14 with asthma, and four healthy controls, all aged 18–65 years.
The participants underwent bronchial provocation tests with methacholine, AMP, and mannitol on three separate occasions, and lung function was measured before and after each test, with a fall of at least 20% in FEV1 indicating a response. Sputum was also collected from the participants after each provocation test and assessed for concentrations of eosinophils and histamine.
The researchers found that none of the patients with EB had a bronchoconstrictor response to any of the provocation tests.
In contrast, four of eight patients with asthma exhibited a positive response to AMP, and seven of 10 asthma patients exhibited a positive response to mannitol. None of the controls responded to the challenges.
After methacholine challenge, sputum histamine concentrations were significantly higher in asthma patients compared with EB patients and controls. There was no significant difference in histamine concentrations or sputum eosinophil levels in any of the groups following AMP or mannitol challenge, compared with methacholine challenge.
Bradding and team conclude: “The airways of patients with EB are not responsive to either direct or indirect bronchial challenge.
“This supports the view that it is the presence of functionally abnormal airway smooth muscle that is the key determinant of BHR in asthma, and that while this may be aggravated by the presence of mucosal airway inflammation, it is not caused by it.”
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By Mark Cowen