Bronchodilation with salbutamol vs bronchial challenge with methacholine in asthma diagnosis
Published online: September 18, 2019
Asthma is one the most prevalent chronic respiratory diseases yet is often misdiagnosed in clinical practice. Diagnosis is based on the combination of recurrent or chronic respiratory symptoms associated with the demonstration of excessive fluctuation in airway caliber over a short period of time. Two common ways to prove this excessive fluctuation are the bronchodilator test and the bronchial methacholine challenge. Whether these two tests provide the same information regarding demographic, functional, and inflammatory features, has not been extensively studied.
In a recent study published in The Journal of Allergy and Clinical Immunology: In Practice, Louis et al directly compare the reversibility to inhaled salbutamol (400 µg) and the methacholine provocation test performed 7-14 days apart on the same population of 194 patients without any maintenance treatment and presenting with a clinical history and symptoms suspicious of asthma. The authors further evaluated the relationships between the two diagnostic tests and patient demographics, serum immunoglobulin E (IgE), systemic inflammatory biomarkers, and fraction of exhaled nitric oxide (FeNO) as well as blood and sputum cell counts.
Baseline average Forced expiratory Volume in one second (FEV1) value was 94% predicted in the study population. A positive methacholine challenge was defined by a provocative concentration (PC20M) ≤ 16 mg/ml and a positive bronchodilator test was defined as an improvement of least 12% and at 200 ml from baseline after 400 µg inhaled salbutamol. Isolated positive methacholine challenge was found in 71%, double positive in 17% while isolated positive reversibility was only seen in 3% of the patients. There was no correlation between PC20M and the magnitude of reversibility to salbutamol. PC20 M was inversely correlated with FeNO and sputum eosinophils while the magnitude of reversibility correlated with serum IgE. Importantly, demographic and immunoinflammatory features were found to be similar in patients selected on the basis of either reversibility or hyperresponsiveness to methacholine, with the proportion of eosinophilic asthma (sputum eosinophils ≥ 3%) reaching 35-40% of the population.
Their study emphasizes the poor sensitivity of the bronchodilator test and the need to perform methacholine challenge in patients suspected of having asthma. It also shows similar demographic and immunoinflammatory features in patients diagnosed by either one of these tests. Finally, it appears that the majority of the patients diagnosed with asthma are actually non eosinophilic, which casts doubts on the utility of T2 inflammatory biomarkers to make an asthma diagnosis.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.