Methacholine and adenosine 5'-monophosphate challenges in preschool children with cough-variant and classic asthma.

Bronchial challenge with different stimuli provides different information and may be used as an adjunct to understand the pathophysiology of cough variant asthma (CVA) in young children in whom the mechanism of disease is still unresolved. This study was designed to investigate the hypothesis that airway hyperresponsiveness (AHR) to methacholine and adenosine 5'-monophosphate (AMP) is similar in preschool children with CVA and classic asthma. We examined airway response to methacholine and AMP in well-defined 3-6-year-old children with CVA (n = 18), classic persistent asthma (n = 31), and healthy controls (n = 10) by transcutaneous oxygen monitorization. The number of AMP responsive children was significantly lower in the group with CVA (38.9%) than classic persistent asthma (67.7%) (P = 0.049). Mean provocative concentration of AMP causing a 15% fall in transcutaneous oxygen tension (PC15PtcO2 AMP) in children with CVA and classic persistent asthma were 234.58 and 36.35 mg/ml, respectively (P = 0.001). None of the healthy children in the control group responded to AMP. The severity of methacholine responsiveness was found similar in CVA and classic persistent asthma groups (P = 0.738). Although both asthma groups showed a similar pattern in methacholine responsiveness, preschool children with CVA were found to differ from children with classic persistent asthma with regard to response profiles to AMP challenge which may point to different pathophysiologic mechanisms of CVA in the young age group.