Bronchial hyperreactivity to methacholine in atopic versus nonatopic asthmatic schoolchildren and preschoolers

Severe bronchial hyperresponsiveness along with house dust mite allergy indicates persistence of asthma in young children

BACKGROUND

Significant risk factors for persistence of asthma later in life are family history of allergies, early allergic sensitization and bronchial hyperresponsiveness (BHR). The evolution of BHR in young children without allergic sensitization and with house dust mite allergy (HDM) was investigated.

METHODS

In this retrospective analysis, electronic charts of 4850 young children with asthma and wheezy bronchitis between 2005 and 2018 were reviewed in order to study all patients ≤6 years with BHR assessed by methacholine provocation tests (MCT) at least once (n = 1175). Patients with more than two follow-up measurements were divided in group 1 (no allergic sensitization; n = 110) and group 2 (HDM allergy; n = 88). Additionally, skin prick test, exhaled nitrite oxide (eNO), and asthma treatment were analyzed.

RESULTS

Forty-seven patients of group 1 aged median 4.3 years and 48 patients of group 2 aged median 4.7 years showed initially severe BHR <0.1 mg. At follow-up, patients with HDM were more likely to show persistence of severe BHR than non-sensitized patients (severe BHR group 1: n = 5 (10.6%) vs. group 2: n = 21 (43.8%), p < .001). In addition, 89.4% of group 1 had mild to moderate or no BHR, compared to only 56.2% of group 2. There was a significant difference in eN0 (median group 1: 9 ppb vs. group 2: 26 ppb, p < .001), at last follow-up. Age, sex, and asthma therapy had no effect on BHR.

CONCLUSION

In young children without sensitization BHR normalizes, whereas HDM allergy indicates a persistence of asthma beyond infancy.

Prevalence of airway hyperresponsiveness and its seasonal variation in children with asthma

BACKGROUND

Airway hyperresponsiveness (AHR) is a key feature of asthma and can be detected using various bronchoprovocation tests. In pediatric populations, the percentage of a positive methacholine challenge test (MCCTs) in children with asthma varies among studies, and some have reported seasonal variability. However, these studies have mostly been conducted in temperate regions. This study evaluated the prevalence of AHR to methacholine and its seasonal variation in asthmatic children in Taiwan, a subtropical country.

METHODS

A total of 276 children with asthma and their MCCT results were retrospectively reviewed. All were diagnosed with asthma and received asthma controllers regularly. They were assigned to four season groups depending in which season MCCTs were administered, with seasons categorized by the Central Weather Bureau of Taiwan. Subgroup analyses, including for sex, age, and atopy level, were compared for seasonal difference.

RESULTS

The prevalence of methacholine hyperresponsiveness was 70.7% (n = 195), and the children who were younger and had higher total serum IgE were more sensitive to methacholine (p = 0.019 and p < 0.005, respectively). No significant difference in AHR prevalence among seasons was observed (p = 0.480). The percentage of borderline, mild, and moderate severity of MCCT results was almost equally distributed among the seasons. In subgroup analysis, the children with a higher IgE level (≥75th percentile of all data) had a higher proportion of positive MCCTs in summer (88.6%, p = 0.016).

CONCLUSION

In total, 70% of the children with asthma in Taiwan had AHR to methacholine, which varied among seasons. Children with a higher total serum IgE level may be more seasonally dependent, particularly in summer.

Clinical phenotypes of bronchial hyperresponsiveness in school-aged children

BACKGROUND

Bronchial hyperresponsiveness (BHR), one of the key features of asthma, has a diverse natural course in school-aged children, but studies on BHR phenotypes are lacking.

OBJECTIVE

To classify BHR phenotypes according to onset age and persistence in children and investigate the characteristics and factors associated with each phenotype in a longitudinal study.

METHODS

This study analyzed 1,305 elementary school children from the Children's Health and Environmental Research (CHEER) study, a 4-year, prospective, follow-up study with 2-year intervals starting at a mean age of 7years. Total serum IgE levels and blood eosinophil counts were measured, and allergy workup, including methacholine challenge tests with the International Study of Asthma and Allergies in Childhood questionnaire, was performed at each survey.

RESULTS

The 4 BHR phenotypes were classified as non-BHR (n = 942 [72.2%]), early-onset transient BHR (n = 201 [15.4%]), late-onset BHR (n = 87 [6.7%]), and early-onset persistent BHR (n = 75 [5.7%]). Early-onset persistent BHR is characterized by an increased eosinophil count, total serum IgE level, sensitization rate, decreased lung function, and increased risk of newly diagnosed asthma during follow-up (adjusted odds ratio, 3.89; 95% confidence interval, 1.70-8.88). The 2 early-onset phenotypes were associated with peripheral airway dysfunction. The late-onset BHR phenotype was related to increased risks of allergic rhinitis symptoms at baseline and later sensitization against inhalant allergens.

CONCLUSION

The early-onset persistent BHR phenotype in school-aged children is associated with high atopic burden and increased risk of newly diagnosed asthma, whereas the late-onset BHR phenotype related with later sensitization and allergic rhinitis symptoms. Diverse BHR phenotypes in children have specific characteristics that require targeted follow-ups.

Prevalence, risk factors, and clinical outcomes of atopic and nonatopic asthma among rural children

BACKGROUND

Because of time and cost constraints, objective classification of atopic and nonatopic asthma has been limited in large epidemiologic studies. However, as we try to better understand exposure-outcome associations and ensure appropriate treatment of asthma, it is important to focus on phenotype-defined asthma classification.

OBJECTIVE

To compare atopic and nonatopic asthma in rural children with regard to risk factors and clinical outcomes.

METHODS

We conducted a cross-sectional study in rural Saskatchewan, Canada, in 2011. Parents of 6- to 14-year-old children completed a health and exposure survey. Skin prick tests were completed in a subsample of 529 children. Asthma was based physician diagnosis. Asthma status was defined as no asthma, nonatopic asthma, and atopic asthma.

RESULTS

Asthma prevalence was 14.7% of which 32.1% of cases were atopic. After adjustment, early respiratory illness and a family history of asthma were predictors of childhood asthma, regardless of atopic status (P < .05). Being overweight and having a dog in the home were associated with an increased risk of nonatopic asthma (P < .05). A mother with a history of smoking increased the risk of atopic asthma (P = .01). Compared with those with nonatopic asthma, in the past 12 months, children with atopic asthma were more likely to report a sneezy, runny, or blocked nose or have shortness of breath (odds ratio >2), whereas those with nonatopic asthma were more likely to have parents who missed work (odd ratio >3). Those with nonatopic asthma had significantly lower forced expiratory volume in 1 second compared w2ith those with atopic asthma.

CONCLUSION

Exposures may contribute differentially to atopic and nonatopic asthma and result in differential clinical presentation or burden. The study of these characteristics is important for etiologic understanding and management decisions.

Bronchial hyperresponsiveness in childhood: A narrative review

Bronchial hyperresponsiveness (BHR) is an important but not asthma-specific characteristic and can be assessed by direct and indirect methods, based on the stimulus causing airway obstruction. BHR has been proposed as a prognostic marker of asthma severity and persistence, and may also be used to control pharmacological management of asthma. The most recent data on the prevalence and development of BHR in childhood and its predictive value for subsequent asthma development in late adolescence and adulthood is discussed in this review. According to the BHR-related scientific articles written in the English language and indexed in the publicly searchable PubMed database, the prevalence of BHR varies based upon the methods used to assess it and the population examined. In general, however, BHR prevalence is reduced as children grow older, in both healthy and asthmatic populations. While asthma can be predicted by BHR, the predictive value is limited. Reduced lung function, allergic sensitization, female sex, and early respiratory illness have been identified as risk factors for BHR. The collective studies further indicate that BHR is a dynamic feature related to asthma, but asymptomatic BHR is also common. Ultimately, the prevalence of BHR varies depending on the population, the environment, and the evaluation methods used. While both the methacholine challenge and the exercise test may predict asthma in adolescence or early adulthood, the predictive value is higher for the methacholine challenge compared to the exercise test. The collective data presented in the present study demonstrate how BHR develops through childhood and its relation to bronchial asthma.

Airway Remodeling in Preschool Children with Severe Recurrent Wheeze

RATIONALE

Airway wall structure in preschoolers with severe recurrent wheeze is poorly described.

OBJECTIVES

To describe airway wall structure and inflammation in preschoolers with severe recurrent wheeze.

METHODS

Flexible bronchoscopy was performed in two groups of preschoolers with severe recurrent wheeze: group 1, less than or equal to 36 months (n = 20); group 2, 36-59 months (n = 29). We assessed airway inflammation, reticular basement membrane (RBM) thickness, airway smooth muscle (ASM), mucus gland area, vascularity, and epithelial integrity. Comparisons were then made with biopsies from 21 previously described schoolchildren with severe asthma (group 3, 5-11.2 yr).

MEASUREMENTS AND MAIN RESULTS

RBM thickness was lower in group 1 than in group 2 (3.3 vs. 3.9 μm; P = 0.02), was correlated with age (P < 0.01; ρ = 0.62), and was higher in schoolchildren than in preschoolers (6.8 vs. 3.8 μm; P < 0.01). ASM area was lower in preschoolers than in schoolchildren (9.8% vs. 16.5%; P < 0.01). Vascularity was higher in group 1 than in group 2 (P = 0.02) and group 3 (P < 0.05). Mucus gland area was higher in preschoolers than in schoolchildren (16.4% vs. 4.6%; P < 0.01). Inflammatory cell counts in biopsies were not correlated with airway wall structure. ASM area was higher in preschoolers with atopy than without atopy (13.1% vs. 7.7%; P = 0.01). Airway morphometrics and inflammation were similar in viral and multiple-trigger wheezers.

CONCLUSIONS

In preschoolers with severe recurrent wheeze, markers of remodeling and inflammation are unrelated, and atopy is associated with ASM. In the absence of control subjects, we cannot determine whether differences observed in RBM thickness and vascularity result from disease or normal age-related development.

Relationship between atopy and bronchial hyperresponsiveness

Both atopy and bronchial hyperresponsiveness (BHR) are characteristic features of asthma. They are also found among non-asthmatic subjects, including allergic rhinitis patients and the general population. Atopy and BHR in asthma are closely related. Atopy induces airway inflammation as an IgE response to a specific allergen, which causes or amplifies BHR. Moreover, significant evidence of the close relationship between atopy and BHR has been found in non-asthmatic subjects. In this article, we discuss the relationship between atopy and BHR in the general population, asthmatic subjects, and those with allergic rhinitis. This should widen our understanding of the pathophysiology of atopy and BHR.

Bronchial Hyperresponsiveness to Methacholine and AMP in Children With Atopic Asthma

Purpose

Bronchial hyperresponsiveness (BHR) is typically measured by bronchial challenge tests that employ direct stimulation by methacholine or indirect stimulation by adenosine 5'-monophosphate (AMP). Some studies have shown that the AMP challenge test provides a better reflection of airway inflammation, but few studies have examined the relationship between the AMP and methacholine challenge tests in children with asthma. We investigated the relationship between AMP and methacholine testing in children and adolescents with atopic asthma.

Methods

The medical records of 130 children with atopic asthma (mean age, 10.63 years) were reviewed retrospectively. Methacholine and AMP test results, spirometry, skin prick test results, and blood tests for inflammatory markers (total IgE, eosinophils [total count, percent of white blood cells]) were analyzed.

Results

The concentration of AMP that induces a 20% decline in forced expiratory volume in 1 second [FEV1] (PC20) of methacholine correlated with the PC20 of AMP (r²=0.189, P<0.001). No significant differences were observed in the levels of inflammatory markers (total eosinophil count, eosinophil percentage, and total IgE) between groups that were positive and negative for BHR to methacholine. However, significant differences in inflammatory markers were observed in groups that were positive and negative for BHR to AMP (log total eosinophil count, P=0.023; log total IgE, P=0.020, eosinophil percentage, P<0.001). In contrast, body mass index (BMI) was significantly different in the methacholine positive and negative groups (P=0.027), but not in the AMP positive and negative groups (P=0.62). The PC20 of methacholine correlated with FEV1, FEV1/forced vital capacity (FVC), and maximum mid-expiratory flow (MMEF) (P=0.001, 0.011, 0.001, respectively), and the PC20 of AMP correlated with FEV1, FEV1/FVC, and MMEF (P=0.008, 0.046, 0.001, respectively).

Conclusions

Our results suggest that the AMP and methacholine challenge test results correlated well with respect to determining BHR. The BHR to AMP more likely implicated airway inflammation in children with atopic asthma. In contrast, the BHR to methacholine was related to BMI.

Alpha-nicotinic acetylcholine receptor and tobacco smoke exposure: effects on bronchial hyperresponsiveness in children

BACKGROUND

The CHRNA 3 and 5 genes on chromosome 15 encode the alpha subunits of the nicotinic acetylcholine receptor, mediating airway cholinergic activity. Polymorphisms are associated with cigarette smoking, chronic obstructive pulmonary disease, and lung cancer.

AIMS

To determine possible associations between CHRNA 3/5 SNP rs8034191 and asthma or lung function in children in one local and one replicate multinational population, and assess if tobacco smoke modified the associations.

MATERIALS AND METHODS

The rs8034191 SNP genotyped in 551 children from the environment and childhood asthma (ECA) birth cohort study in Oslo, Norway, and in 516 families from six European centers [the Genetics of Asthma International Network (GAIN) study] was tested for genotypic or allelic associations to current or history of asthma, allergic sensitization (≥ one positive skin prick tests), bronchial hyperresponsiveness (BHR), and lung function (FEV(1%) of predicted and FEV(1) /FVC ratio over/ below the 5th percentile).

RESULTS

Although the TT and CT genotypes at SNP rs 8034191 were overall significantly associated with BHR (OR = 3.9, 95% CI 1.5-10.0, p = 0.005), stratified analyses according to exposure to maternal smoking in-utero or indoor smoking at 10 yrs of age showed significant association (OR = 4.4, 95% CI 1.5-12.6, p = 0.006 and OR 5.6, 95% CI 1.7-18.5, p = 0.004, respectively) only in the non-exposed and not in exposed children. The SNP-BHR association was replicated in the non-tobacco-smoke-exposed subjects in one of the GAIN centers (BHR associated with the T allele (p = 0.034)), but not in the collated GAIN populations. Asthma, allergic sensitization, and lung function were not associated with the rs8034191 alleles.

CONCLUSION

An interaction between tobacco smoke exposure and a CHRNA3/5 polymorphism was found for BHR in children, but CHRNA3/5 was not associated with asthma or lung function.

Interaction between bronchiolitis diagnosed before 2 years of age and socio-economic status for bronchial hyperreactivity

OBJECTS

The prevalence of asthma has increased in recent decades globally. The objective of the present study is to elucidate whether hospitalization for bronchiolitis in infancy and low socioeconomic status interact for bronchial hyperreactivity during teenage years.

METHOD

We studied 522 children age 13-14 years attending schools in rural and urban areas to investigate the risk factors for bronchial hyperreactivity (BHR), defined as a provocation concentration of methacholine that causes a decrease of 20% (PC(20)) in forced expiratory volume within 1 second. Clinical examination, skin prick test, spirometry, and methacholine challenge were performed on all study subjects, who provided written consent. We used multivariate logistic regression to investigate the risk factors for BHR, and analyze the interaction between hospitalization for bronchiolitis in infancy and low socioeconomic status.

RESULTS

Forty-six (10.3%) positive BHR cases were identified. In the multivariate logistic analysis, as independent predictors of BHR, adjusted odds ratio of bronchiolitis diagnosed before 2 years of age in low income families was 13.7 (95% confidence interval, 1.4 to 135.0), compared to reference group, controlling for age, gender, parental allergy history, skin prick test, and environmental tobacco smoke (ETS) exposure. Interaction was observed between bronchiolitis before 2 years old and low socioeconomic status on children's bronchial hyperreactivity (p-interaction=0.025).

CONCLUSIONS

This study showed that bronchiolitis diagnosed before 2 years of age and low socioeconomic status interacted on children's bronchial hyperreactivity. Prevention of acute respiratory infection in early childhood in low socioeconomic status is important to prevent BHR as a precursor of asthma.