Comparison of methacholine and adenosine inhalation challenge in patients with suspected asthma

Bronchial hyperresponsiveness is usually measured by bronchial challenge with direct (e.g. methacholine) and indirect (e.g. adenosine) agonists. A prospective, randomized, crossover, single-blind study was performed to compare both methods in the first diagnosis of asthma.

Fifty-seven patients, in which asthma was suspected, were selected (21 male, 36 female). Fifty-four underwent both challenges following the five-breath dosimeter protocol. PC20 was calculated according to ATS guidelines. Data of symptoms developed during the challenge, PC20 methacholine and adenosine, and FEV1 improvement after bronchodilator therapy were recorded.

Symptoms at consultation were consistent with asthma in 68.4% patients, asthma and rhinitis in 29.8% and exercise-induced asthma in 1.8%. Atopy was reported in 93%; 49.1% had family history of atopy and 26.3% of asthma. The most frequent symptoms developed during the challenge were cough (40.4% with adenosine and 20.4% with methacholine) and wheezing (26.3% and 7.4% respectively), statistically significant differences. Bronchial challenge with MCh resulted positive in 44.4% of the patients and positive with AMP in 50%. Every patient with negative result to adenosine, was also negative to methacholine. In 94.4% subjects the result of both challenges was concordant (kappa index = 0.889). PC20 in both challenges showed poor linear correlation (Pearson r = 0.43, p < 0.05). Positivity of both challenges was only associated with having a positive skin prick test to danders (p = 0.001). Percentage of improvement after bronchodilator was 34.9% (SD12.2%) with adenosine challenge and 33.9% (SD17.9%) with methacholine (differences non statistically significant).

Concordance in the result of both techniques is very high. Cough and wheezing are more frequent with adenosine, though not severe. PC20 with both techniques shows poor linear correlation.