Comparison of ΔFVC between patients with allergic rhinitis with airway hypersensitivity and patients with mild asthma

Background: In asthmatic individuals, airway sensitivity and maximal airway response are increased. Airway sensitivity is usually evaluated by measuring the provocation concentration of inhaled methacholine or histamine that causes a decrease in forced expiratory volume in 1 second of 20% (PC₂₀). The percentage decrease in forced vital capacity at the PC₂₀ (ΔFVC) has been proposed as a surrogate marker for maximal airway response. Individuals with allergic rhinitis and no clinical evidence of asthma frequently exhibit airway hypersensitivity. Objective: To compare the ΔFVC between patients with allergic rhinitis and mild asthmatic patients with a similar degree of airway hypersensitivity. Methods: A retrospective analysis of methacholine challenge test data from 72 children with allergic rhinitis and airway hypersensitivity (methacholine PC₂₀ <16 mg/mL) (rhinitis group) and from 72 children with mild atopic asthma matched to the rhinitis group regarding the methacholine PC₂₀ (asthma group). The ΔFVC was calculated on the concentration-response curve to methacholine. Results: The mean ± SD ΔFVC was significantly lower in the rhinitis group (15.0% ± 3.6%) vs the asthma group (17.4% ± 5.3%) (P = .002). There was no significant correlation between the ΔFVC and PC₂₀ in the rhinitis (r = -0.101; P = .41) and asthma (r = -0.023; P = .85) groups when 2 patients with PC₂₀ less than 1 mg/mL were excluded from each group. Conclusions: Patients with allergic rhinitis and airway hypersensitivity had a significantly lower ΔFVC than methacholine PC₂₀-matched mild asthmatic patients, suggesting that the level of maximal airway response in patients with allergic rhinitis is lower than that in mild asthmatic patients with a similar degree of airway hypersensitivity.