Bronchial hyperreactivity in cystic fibrosis and asthma.

We studied 113 patients with CF and compared their responsiveness to inhaled 
methacholine to that of 50 asthmatic children and 26 normal children. 
Positive responses to MCh occurred in 51% of the patients with 
CF and 98% of those with asthma. There was a significant 
correlation between a positive response to MCh in CF and poor 
pulmonary function. There was no relationship between allergic rhinitis or positive 
allergen skin tests and a positive MCh response. Dose-response curves and 
time course to MCh challenge differed in CF and asthma. Bronchial 
hyperreactivity is thus common in CF but is different from that 
in asthma. 