Peripheral obstruction without airflow limitation is rare and not specific to asthma in children.

Peripheral (or small) airway obstruction (PAO) is considered a marker of childhood asthma but the techniques able to directly measure it are rarely used in routine. Usual spirometry and plethysmography can detect a certain degree of PAO when reduced forced vital capacity (FVC) is associated to normal forced expiratory volume in 1 s (FEV1 ) to FVC ratio, and normal total lung capacity (TLC). The frequency of this functional pattern has never been studied in different pediatric respiratory conditions. To assess the prevalence and outcome of PAO in children with different diseases or symptoms, we retrospectively extracted from our database all files of Caucasian subjects encompassing spirometry and plethysmography measurements. Spirometry patterns (normal, airflow limitation [AFL; low FEV1 /FVC], low FVC [with normal FEV1 /FVC]) and final functional patterns (normal, AFL, PAO, restrictive [low TLC], or mixed) were described. We included 4394 files recorded in 1794 children (median [IQR] age: 10.7 [9.2-12.9] years). At inclusion, 125 (7%) children had low FVC of which 56 (44.8%, and 3.1% [95% CI 2.3-3.9] of the whole population) had PAO. PAO prevalence increased with age (OR (95% CI) per 2-year-increase: 2.26 (1.59-3.23); p < .001), and was more frequent in chronic bronchial diseases other than asthma (1.6% vs. 8.0%). On repeated tests, PAO frequently normalized (26.1%) or persisted (43.5%), but it less often progressed into AFL (13%) or restrictive (13%) patterns. PAO is an infrequent nonspecific and persistent functional pattern. Its prevalence increases with age and in diagnosis of chronic respiratory diseases other than asthma.