Airway responsiveness to methacholine and risk of asthma in patients with allergic rhinitis

To find out whether airway hyperresponsiveness is associated with a greater risk of asthma in subjects with allergic rhinitis, 66 nonasthmatic patients with allergic rhinitis underwent inhalation challenge with methacholine. Each patient was reevaluated prospectively at least once each year and a diagnosis of asthma was accepted if the subject developed episodic wheezing and/or cough plus airway obstruction and at least a 15% increase in FEV1 after inhaled salbutamol. Those subjects who developed asthma and ten individuals who did not develop asthma were rechallenged after the first asthma symptoms or at the end of the followup period, respectively. Risk of developing asthma during the followup period (mean of 43.8 months, range 36 to 70) was similar (P > .05) in those individuals who previously had airway hyperresponsiveness (2 of the 19 patients), when compared with subjects who were previously nonresponders (4 of the 47 patients). Further, in those subjects who developed asthma, geometric mean (range) PC20 decreased from 11.75 (0.40 to 50) during the initial evaluation to 1.66 (0.15 to 11.07) mg/mL after the first asthma symptoms (P < .05). No significant modifications of PC20 were detected in subjects who did not develop asthma. We conclude that a single determination of methacholine PC20 is not a reliable marker of the subsequent development of asthma in patients with allergic rhinitis.