Background Airway hyperresponsiveness to pharmacological agonists is a common feature in subjects with allergic rhinitis.
Objective The aim of this study was to investigate differences in threshold value and shape of the concentration-response curves to methacholine between subjects with perennial allergic rhinitis and subjects with seasonal rhinitis.
Methods We studied a sample of 72 non-asthmatic patients with allergic rhinitis. They were subdivided into two groups: subjects with only seasonal symptoms and skin sensitization to grass and/or Parietaria pollen allergens (seasonal group, n= 38), and subjects with perennial symptoms and skin sensitization to house dust mite, alone or with other allergens (perennial group, n = 34). They were challenged with methacholine (up to 200mg/mL), and concentration-response curves were characterized by the threshold value (PC20= provocative concentration of methacholine required to produce a 20% fall in FEV1) and maximal response plateau, if possible. The measurements in the seasonal group were done within the pollen season.
Results The geometric mean methacholine PC20 for subjects of the perennial group was 6.9mg/mL, compared with 23.4mg/mL in subjects of the seasonal group (P 0.01). A plateau response was detected in 16 subjects of the perennial group and in 28 subjects of the seasonal group (p 0.05). Moreover, the level of plateau was higher in subjects of the perennial group when compared with subjects of the seasonal group (23.8 ±2.0% vs 19.2 ±1.6%, P 0.05).
Conclusion In subjects with allergic rhinitis, sensitization to perennial allergens is associated not only with lower methacholine threshold values, but also with lower prevalence and higher level of plateau than sensitization to pollen allergens.