The clinical outcome of asymptomatic airway hyperresponsiveness (AHR) first detected in childhood is sparsely reported, with conflicting results. We used a birth cohort of 1,037 children followed to age 26 years to assess the clinical outcome of asymptomatic AHR to methacholine first documented in study members at age 9 years.
Of 547 study members who denied wheezing symptoms ever at age 9 years, 41 (7.5%) showed AHR. Forty showed methacholine responsiveness, with a provocation concentration of methacholine that elicted a 20% drop in forced expired volume in 1 sec (PC20) ≤ 8 mg/mL, and one had baseline airway obstruction with a bronchodilator response exceeding 10%. Of these 41 study members, 18 (44%), 11 (27%), and 4 (10%) maintained AHR in 1, 2, and 3 later assessments, respectively, while 23 (56%) manifested AHR only at age 9. Compared with asymptomatic study members without AHR, those with asymptomatic AHR at age 9 years were more likely to report asthma and wheeze at any subsequent assessment, were more likely to have high IgE levels and eosinophils at ages 11 and 21, and more often demonstrated positive responses to skin allergen testing at ages 13 and 21 years. Persistent AHR at later assessments increased these likelihoods further.
In conclusion, asymptomatic children with AHR are more likely to develop asthma and atopy later in life compared with asymptomatic children without AHR. Persistent AHR, even though initially asymptomatic, was associated with an even greater increased risk of development of asthma. We suggest that rather than considering AHR as a marker of asthma, it should be regarded as a parallel pathological process that may lead to subsequent symptoms and clinical evidence of asthma. Pediatr Pulmonol. 2002; 34:164–171. © 2002 Wiley-Liss, Inc.