Spontaneous improvement in bronchial responsiveness and its limit during preadolescence and early adolescence in children with controlled asthma.

To study whether improvement in bronchial responsiveness contributes to outgrowing of asthma, PC20-histamine was measured longitudinally in nine nonsteroid-dependent asthmatic children (six boys, three girls), aged 8.1 to 9.8 years (mean, 9.2 years) at the beginning of the study. The measurement was discontinued when final inhaled histamine concentration in at least two consecutive measurements did not exceed the previous highest one. Two or more doubling concentration differences in inhaled histamine is regarded as significant in our center. Mean (SD) study period was 3.6 (0.8) years, interval of the measurements was 10.6 (2.3) months. Geometric mean of PC20-histamine at the beginning was 0.39 mg/ml. PC20-histamine improved significantly in seven of nine patients during the study period, though best values were less than 8 mg/ml in all. Mean (SD) age reaching the highest final concentration was 11.0 (0.8) years. These data suggest that the improvement in bronchial responsiveness may be one of mechanisms in the outgrowing of asthma around adolescence.