Childhood cough variant asthma and its relationship to classic asthma.
BACKGROUND
In pediatrics, some patients with chronic cough who have no evidence of a causative disease are diagnosed as having cough variant asthma (CVA). The precise prognosis of infants and children with CVA, however, is still unclear.


OBJECTIVE
To evaluate the relationship between CVA and classic asthma in childhood.


METHODS
To diagnose CVA, we performed a methacholine inhalation challenge with use of a transcutaneous oxygen pressure (tcPO2) monitoring system in 100 children with chronic cough, and 75 children (45 boys and 30 girls; mean age, 5.7 years) were diagnosed as having CVA. These patients underwent follow-up monitoring for more than 3 years to ascertain whether classic asthma developed. For comparison, 53 age-matched children with classic asthma (30 boys and 23 girls; mean age, 5.6 years) and 30 age-matched control subjects (12 boys and 18 girls; mean age, 5.5 years) also participated in this study. Consecutive doses of methacholine were doubled until a 10% decrease in tcPO2 from the baseline was reached. The cumulative dose of methacholine at the inflection point of tcPO2 (Dmin-PO2) was considered to represent the sensitivity of tcPO2 to inhaled methacholine.


RESULTS
After 3 years or more of follow-up assessments, 52 of the 75 patients answered our questionnaire. Of the responding patients, 28 had been diagnosed as having classic asthma. A significant difference was noted in the age at onset of CVA between the children in whom classic asthma developed (the asthma-developed group) and those in whom classic asthma did not develop (the asthma-free group). No statistically significant differences in Dmin-PO2 between the asthma-developed group and the asthma-free group or between the girls and the boys, however, were foun


CONCLUSIONS
This study showed that 75% of children with chronic cough had CVA, that classic asthma developed in 54% of the children with CVA, and that it is not the severity of bronchial hyperresponsiveness in CVA but the age at onset of CVA that is a risk factor for the development of classic asthma in childhood CVA.
Todokoro
Makoto
M
Department of Pediatrics, Gunma University School of Medicine, Maebashi, Japan. mochihi@med.gunma-u.ac.jp
Mochizuki
Hiroyuki
H
Tokuyama
Kenichi
K
Morikawa
Akihiro
A
D000280:Administration, Inhalation; D000293:Adolescent; D000367:Age Factors; D001249:Asthma / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D016535:Bronchial Hyperreactivity / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D001985:Bronchial Provocation Tests; D016085:Bronchoconstrictor Agents / Q000009:adverse effects; D002648:Child; D002669:Child Welfare; D002675:Child, Preschool; D002908:Chronic Disease; D003371:Cough / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D007229:Infant Welfare; D008297:Male; D016210:Methacholine Chloride / Q000009:adverse effects; D010100:Oxygen / Q000378:metabolism; D012720:Severity of Illness Index; D013223:Statistics as Topic; D011795:Surveys and Questionnaires
D016085:Bronchoconstrictor Agents; D016210:Methacholine Chloride; D010100:Oxygen