Seasonal variability of non-specific bronchial responsiveness in asthmaticpatients with allergy to house dust mites

The aim of the study was to assess the seasonal variability of non-specific bronchial responsiveness to methacholine in allergic asthma. One hundred s ixty-five patients (83 male and 82 female) entered the study: 86 subjects ( group A) with allergy exclusively to,mites and 79 (group B) with concomitan t allergy to pollens, e.g., "Graminae" and "Parietaria." Inclusion criteria were the absence of sensitization to other allergens, no smoking habit, wi thdrawal from steroids, bronchodilators, sodium cromoglycate, and antihista mines for at least four weeks before enrollment, FEVI > 70% of the predicte d value, and absence of other respiratory diseases and of upper and lower r espiratory tract infections for at feast one month before the methacholine challenge. None of the patients had been previously treated with specific i mmunotherapy. Subjects of each group (A and B) underwent methacholine chall enge at first visit and were divided into four subgroups according to the p eriod when the challenge was performed. Subgroups Al and B1 performed the c hallenge in December January, and February; subgroups A2 and B2 in March, A pril, and May; subgroups A3 and B3 in June, July, and August; subgroups A4 and B4 in September October; and November. PD20 values were expressed as th e natural logs of the cumulative dose of methacholine causing at least a 20 % fall in FEVI. Statistical analysis was carried out using multiple group a nalysis and Strident's t-test. Results showed that the highest non-specific bronchial responsiveness was observed in autumn (ln PC20 = 4.54 +/- 1.51) in patients allergic to mites only (group A), and in summer (ln PC20 = 4.72 +/- 2.11) in those of group B. Multiple group analysis showed statistical significant differences between subgroups within each group (group A, p = 0 .039; group B, p < 0.001). In patients allergic exclusively to house dust m ites (group A), multiple comparisons and Student's t-test showed statistica lly significant differences between nonspecific bronchial responsiveness (N SBR) assessed in autumn and those of other seasons (winter p = 0.002; sprin g, p < 0.001; summer, p = 0.082). These results confirm that the level of a llergen exposure may influence NSBR. Mite-allergic patients showed ara incr ease of NSBR in autumn, possibly as a consequence of higher indoor mite con centration. However, mite- and grass-allergic patients had wider variations of NSBR, possibly reflecting changes in seasonal pollen concentration.