Bronchial hyperreactivity in cystic fibrosis [letter].

Mitchell and co-workers conclude that bronchial hyperreactivity is common in cystic fibrosis 
(CF) but is different from that in asthma. Their data were 
interesting, but I do not agree with their conclusion. One can 
interpret these data as suggesting a common reversible component in both 
patient groups, and perhaps a common denominator in mechanism. Because of 
certain problems with baseline measurements and withholding of medication, it seems 
that the conclusion of Mitchell et al may not be well 
supported. - We felt justified in studying those patients with a 
low baseline FEV (forced expiratory volume in one second), since a 
subject's bronchial response to methacholine remains stable even if these is 
moderate fluctuation both in initial specific airway conductance and in the 
severity of the disease. We feel that withholding the drug for 
a longer period would not have affected the comparisons. Although there 
might be a common underlying mechanism in bronchial hyperreactivity in asthma 
and cystic fibrosis, our data showed a number of differences between 
the two groups of patients. Although these differences would not exclude 
a common mechanism in bronchial hyperreactivity in the two diseases, the 
existence of the differences should lead to caution in concluding that 
there is a common underlying mechanism in the bronchial hyperreactivity in 
the two diseases. 