New developments in work-related asthma

Novel approaches in occupational asthma diagnosis and management

PURPOSE OF REVIEW

To describe the recent findings of the last 2 years on the epidemiology and phenotypes of occupational asthma, as well as new developments in its diagnosis and management.

RECENT FINDINGS

Data from nine longitudinal studies showed a population attributable fraction for the occupational contribution to incident asthma of 16%. The main phenotypes of occupational asthma are: occupational asthma caused by high-molecular-weight (HMW) or low-molecular-weight (LMW) agents, irritant-induced asthma and occupational asthma-chronic obstructive pulmonary disease overlap. Among the variety of causative agents of occupational asthma, food-derived components are increasingly being reported, accounting for up to 25% cases of occupational asthma and/or occupational rhinitis. Recently, a specific inhalation challenge (SIC)-independent model has been developed to calculate the probability of occupational asthma diagnosis in workers exposed to HMW agents. In this model, work-specific sensitization, bronchial hyperresponsiveness, inhaled corticosteroid use, rhinoconjunctivitis and age 40 years or less were the most relevant predictive factors. Specific IgE measurements showed a pooled sensitivity of 0.74 and a specificity of 0.71 in the diagnosis of occupational asthma for HMW agents, while a lower sensitivity (0.28) and a higher specificity (0.89) was shown for LMW agents. Cessation of exposure to workplace sensitizers is the cornerstone of management of work-related conditions.

SUMMARY

An early and precise diagnosis of occupational asthma is crucial, allowing appropriate management and implementation of preventive strategies.

Progress in Occupational Asthma

Occupational asthma (OA) represents one of the major public health problems due to its high prevalence, important social and economic burden. The aim of this review is to summarize current data about clinical phenotypes, biomarkers, diagnosis and management of OA, a subtype of work-related asthma. Most studies have identified two phenotypes of OA. One is sensitizer-induced asthma, occuring after a latency period and caused by hypersensitivity to high- or low-molecular weight agents. The other is irritant-induced asthma, which can occur after one or more exposures to high concentrations of irritants without latency period. More than 400 agents causing OA have been identified and its list is growing fast. The best diagnostic approach for OA is a combination of clinical history and objective tests. An important tool is a specific inhalation challenge. Additional tests include assessments of bronchial hyperresponsiveness to methacholine/histamine in patients without airflow limitations, monitoring peak expiratory flow at- and off-work, sputum eosinophil count, exhaled nitric oxide measurement, skin prick tests with occupational allergens and serum specific IgE. Treatment of OA implies avoidance of exposure, pharmacotherapy and education. OA is a heterogeneous disease. Mechanisms of its different phenotypes, their diagnosis, role of new biomarkers and treatment require further investigation.

Possible risk factors for poor asthma control assessed in a cross-sectional population-based study from Telemark, Norway

This cross-sectional study of the general population of Telemark County, Norway, aimed to identify risk factors associated with poor asthma control as defined by the Asthma Control Test (ACT), and to determine the proportions of patients with poorly controlled asthma who had undergone spirometry, used asthma medication, or been examined by a pulmonary physician. In 2014–2015, the study recruited 326 subjects aged 16–50 years who had self-reported physician-diagnosed asthma and presence of respiratory symptoms during the previous 12 months. The clinical outcome measures were body mass index (BMI), forced vital capacity (FVC) and forced expiratory volume in one second (FEV₁), fractional exhaled nitric oxide (FeNO), immunoglobulin E (IgE) in serum and serum C-reactive protein (CRP). An ACT score ≤ 19 was defined as poorly controlled asthma. Overall, 113 subjects (35%) reported poor asthma control. The odds ratios (ORs) and 95% confidence intervals (CIs) for factors associated with poorly controlled asthma were: self-reported occupational exposure to vapor, gas, dust, or fumes during the previous 12 months (OR 2.0; 95% CI 1.1–3.6), body mass index ≥ 30 kg/m² (OR 2.2; 95% CI 1.2–4.1), female sex (OR 2.6; 95% CI 1.5–4.7), current smoking (OR 2.8; 95% CI 1.5–5.3), and past smoking (OR 2.3; 95% CI 1.3–4.0). Poor asthma control was also associated with reduced FEV₁ after bronchodilation (β –3.6; 95% CI –7.0 to –0.2). Moreover, 13% of the participants with poor asthma control reported no use of asthma medication, 51% had not been assessed by a pulmonary physician, and 20% had never undergone spirometry. Because these data are cross-sectional, further studies assessing possible risk factors in general and objectively measured occupational exposure in particular are needed. However, our results suggest that there is room for improvement with regards to use of spirometry and pulmonary physician referrals when a patient’s asthma is inadequately controlled.

Basophil activation testing in occupational respiratory allergy to low molecular weight compounds

PURPOSE OF REVIEW

There is an unmet need for better immunological tests in cases of suspected occupational asthma to many workplace chemicals; here we consider the basophil activation test (BAT), a potential alternative to the detection of specific IgE antibodies.

RECENT FINDINGS

BAT is fairly widely used in general allergy services; and there is increasing experience of its use in the diagnosis of occupational allergy to low molecular weight agents and chemicals including wood dusts, persulphates, antibiotics and latex.

SUMMARY

There is potential for BAT to become a useful tool in the clinical consideration of occupational asthma and of its mechanisms, and even to take a place in a Bayesian-based diagnostic algorithm. Further development will only occur if specialist centres with appropriate facilities, and preferably in collaboration, contemplate its use.

Occupational asthma: clinical phenotypes, biomarkers, and management

PURPOSE OF REVIEW

This review focuses on new findings in the clinical and inflammatory aspects that can help to better identify the different phenotypes of work-related asthma and the development of specific biomarkers useful in diagnosis and follow-up.

RECENT FINDINGS

Studies on phenotyping of occupational asthma, a subtype of work-related asthma, have mainly compared the clinical, physiological, and inflammatory patterns associated with the type of agent causing occupational asthma, namely, high-molecular-weight and low-molecular-weight agents. Most of this research has found that patients with occupational asthma due to high-molecular-weight agents have an associated presence of rhinitis, conjunctivitis, atopy, and a pattern of early asthmatic reactions during specific inhalation challenge. The inflammatory profile (blood eosinophils, sputum cell count, or exhaled nitric oxide) may be similar when occupational asthma is caused by either type of agent. In some studies, severity of asthma and exacerbations have been associated with exposure to low-molecular-weight agents. The most reliable biomarkers in diagnosis and follow-up are eosinophilia in induced sputum and exhaled nitric oxide.

SUMMARY

There are several phenotypes, characterized by its pathogenesis and inflammatory profile. Avoidance of the causative agents does not warrant complete recovery of occupational asthma. Treatment with biologic agents may be considered in severe occupational asthma.

Serial fractional exhaled nitric oxide measurements off and at work in the diagnosis of occupational asthma

BACKGROUND

Fractional exhaled nitric oxide (FeNO) before and after specific inhalation challenge has been postulated as an additional tool in the diagnosis of occupational asthma (OA), but little is known about serial FeNO measurements at home and at work. The aim of the present study was to assess the contribution of serial measurements of FeNO off and at work toward the diagnosis of OA.

METHODS

Forty-one subjects with suspected (n = 35) or diagnosed (n = 6) OA performed FeNO measurements once daily during a 2-week holiday and a subsequent 2-week work period. A work-related increase in FeNO by 20 ppb (parts per billion) or more was considered positive. Subjects with negative or doubtful specific inhalation challenge but a FeNO increase of 20 ppb or more were evaluated individually by an overall expert rating taking into account all available information.

RESULTS

Seven of 35 subjects (20%) with suspected and three of six subjects (50%) with diagnosed OA showed a work-related FeNO increase of 20 ppb or more. Six of the seven with suspected OA were reclassified as having an OA diagnosis by the overall expert rating which also considered these FeNO changes.

CONCLUSIONS

Serial FeNO measurements off and at work provide complementary information in the diagnosis in about one-fifth of cases with suspected OA, especially if specific inhalation challenges are negative or cannot be performed.

Non-eosinophilic asthma: current perspectives

Although non-eosinophilic asthma (NEA) is not the best known and most prevalent asthma phenotype, its importance cannot be underestimated. NEA is characterized by airway inflammation with the absence of eosinophils, subsequent to activation of non-predominant type 2 immunologic pathways. This phenotype, which possibly includes several not well-defined subphenotypes, is defined by an eosinophil count <2% in sputum. NEA has been associated with environmental and/or host factors, such as smoking cigarettes, pollution, work-related agents, infections, and obesity. These risk factors, alone or in conjunction, can activate specific cellular and molecular pathways leading to non-type 2 inflammation. The most relevant clinical trait of NEA is its poor response to standard asthma treatments, especially to inhaled corticosteroids, leading to a higher severity of disease and to difficult-to-control asthma. Indeed, NEA constitutes about 50% of severe asthma cases. Since most current and forthcoming biologic therapies specifically target type 2 asthma phenotypes, such as uncontrolled severe eosinophilic or allergic asthma, there is a dramatic lack of effective treatments for uncontrolled non-type 2 asthma. Research efforts are now focusing on elucidating the phenotypes underlying the non-type 2 asthma, and several studies are being conducted with new drugs and biologics aiming to develop effective strategies for this type of asthma, and various immunologic pathways are being scrutinized to optimize efficacy and to abolish possible adverse effects.

Addressing Molecular Diagnosis of Occupational Allergies

PURPOSE OF REVIEW

Numerous clinically relevant allergenic molecules enhance the performance of specific (s) IgE tests and improve the specificity of allergy diagnosis. This review aimed to summarize our current knowledge of the high-molecular-weight allergens involved in the development of occupational asthma and rhinitis and to critically analyze the contribution of component-resolved diagnosis in the management of these conditions.

RECENT FINDINGS

There is a lack of standardization and validation for most available extracts of occupational agents, and assessment of sIgE reactivity to occupational allergen components has been poorly investigated, with the notable exception of natural rubber latex (NRL) and wheat flour. In the case of NRL, the application of recombinant single allergens and amplification of natural extracts with stable recombinant allergens improved the test sensitivity. IgE-sensitization profile in patients with baker's asthma showed great interindividual variation, and extract-based diagnostic is still recommended. For other occupational allergens, it remains necessary to evaluate the relevance of single allergen molecules for the sensitization induced by occupational exposure. Progress has been made to characterize occupational allergens especially NRL and wheat, although there is still an unmet need to increase the knowledge of occupational allergens, to include standardized tools into routine diagnostic, and to evaluate their usefulness in clinical practice.

Diagnostic Accuracy of Inflammatory Markers for Diagnosing Occupational Asthma

BACKGROUND

The assessment of airway responsiveness and inflammation is key to the investigation of occupational asthma (OA).

OBJECTIVE

We sought to assess and compare the diagnostic accuracies of the blood and sputum eosinophil counts and the methacholine challenge for the diagnosis of OA.

METHODS

We conducted a retrospective study assessing 618 patients who underwent specific inhalation challenges (SICs) for symptoms suggestive of OA between 2000 and 2015. A sputum induction and a methacholine challenge were performed before and after SICs. Blood samples were collected in all subjects before the SICs and in 100 subjects before and after SICs. The diagnostic accuracies of blood and sputum eosinophil counts and methacholine challenge were calculated for diagnosing OA.

RESULTS

The change in blood eosinophil count failed to differentiate workers with positive and negative SICs. The change in sputum eosinophil counts induced by the exposure to the offending agent had the highest diagnostic accuracy (receiver operating characteristic area under the curve: 86% [95% confidence interval: 0.8-0.9, P < .001]) for diagnosing OA compared with changes in concentration of methacholine inducing a 20% fall in forced expiratory volume in 1 second (PC₂₀) and blood eosinophils. Combining a 2-fold or greater decrease in PC₂₀ or a 3% or greater increase in sputum eosinophil count achieved a sensitivity of 84% and a specificity of 74% with a negative predictive value of 91% for the diagnosis of OA.

CONCLUSIONS

Blood eosinophil counts do not appear to be an effective aid for diagnosing OA. The performance of both sputum cell count analysis and a methacholine challenge before and after exposure to the offending agent may represent an effective alternative in diagnosing OA when SICs are unavailable.