Comparison of Methacholine and Mannitol to Predict Exercise-Induced Bronchoconstriction in Children with Asthma

Background: Bronchial hyper-responsiveness (BHR) can be assessed by performing bronchial provocation tests (BPTs) with direct stimuli such as methacholine, or indirect stimuli such as mannitol. The aim of this study was to examine the diagnostic properties of methacholine and mannitol challenge to predict exercise-induced bronchoconstriction (EIB) in athmatic children. 

Methods: Eighty-nine asthmatic children between 6 and 15 years old were enrolled. Exercise challenges were conducted in all subjects. 72 subjects underwent methacholine BPTs and 36 subjects underwent mannitol BPTs. 18 subjects underwent both mannitol and methacholine BPTs. BHR to exercise was defined as a ≥ 15% fall in FEV1 after exercise, to methacholine a PC20 ≤ 25 mg/ml and to mannitol a 15% fall in FEV1 at ≤ 635 mg. 

Results: Thirty-seven (41.6%, 37/89) subjects with asthma had a positive exercise challange test. The maximum decreases in %FEV1 after exercise were positively correlated with mannitol PD15 (r=-0.540, p=0.038) but not correlated with methacholine PC20 in asthmatics with EIB. The sensitivity of methacholine to identify EIB was 93.3% (28/30) and the specificity was 52.4% (22/42). The sensitivity of mannitol was 66.7% (14/21) and the specificity was 40.0% (6/15).

Conclusion: The maximum decreases in %FEV1 after exercise was significantly correlated with mannito PD15 but not with methacholine PC20. However, methacholine is more sensitive than mannitol to identify EIB in asthmatic children.