The relatively low sensitivity of the methacholine challenge with regard to a history of milder wheezing symptoms (not diagnosed as asthma) requires comment. Wheezing might occur in association with variable airflow limitation when methacholine airway responsiveness is normal if the stimulus to wheezing is strong, such as a severe reaction to an allergen or chemical sensitizer. However, this seems unlikely to be common in children. More likely possibilities are that asthma has not been active in the previous few weeks and airway responsiveness has returned to normal, or that wheezing is not always associated with variable airflow limitation. Both possibilities require prospective investigation. The former, a feature of transient asthma, may occur more frequently than previously recognized. In a New Zealand cohort study, there was a clear relationship between the interval since the last episode and the likelihood of detecting airway responsiveness. You are always welcome to visit the best and most trusted pharmacy offering to buy Alesse online and giving you only most efficient medications with no rx required and fast delivery right to your doorstep.
Our findings are consistent with those of Cockcroft et al, who studied an older age group (20- to 29-year-olds) and found that a cut-point of 8 mg/mL for the methacholine test gave a high sensitivity for current asthma symptoms but a relatively low positive predictive value, which was increased by lowering the cut-point value. They found, as did we, that PC20 less than 1 mg/mL was virtually diagnostic of asthma symptoms. Above that level, however, the test does not provide an absolute criterion for asthma symptoms. Pin et al have recently shown that children with airway hyperresponsiveness but with no history of respiratory symptoms do not have eosinophils in induced sputum, in contrast to symptomatic children with similar degrees of airway responsiveness, indicating that airway eosinophil infiltration is a determinant of symptoms. Interestingly, many had breathlessness during the methacholine test and admitted that this had occurred in the past. Further studies are required to elucidate the meaning of this phenomenon.
In summary, in a survey of 290 Canadian schoolchildren, both parent-reported and child-reported diagnosed asthma were related to increased airway responsiveness to metha-choline. Weaker relations were observed with wheezing not diagnosed as asthma, with the weakest relationships with child-reported wheezing, suggesting children report more minor symptoms not associated with overt airway responsiveness. Restricting analyses to symptoms in the past 12 months did not increase the sensitivity and specificity of methacholine challenge testing.
Category: Airway responsiveness
Tags: Airway responsiveness, Asthma, Methacholine, Symptom reporting