Occupational asthma: what have we learned?

Occupational asthma is one of the most frequent work-related diseases and may represent between 2% and 6% of all cases of asthma. It is defined as asthma causally and specifically related to exposure to airborne dusts, gases, vapors, or fumes in the working environment. Because it may cause long-lasting disability, it is important to properly identify affected workers and to withdraw them from exposure to the sensitizing agent as soon as possible. Although the history is the clue to the diagnosis, it is not sensitive or specific. The diagnosis should be confirmed by objective means, essentially by monitoring of peak expiratory flow and nonallergic bronchial responsiveness or by specific inhalation challenges. In this article the author reviews the investigation of occupational asthma.

Immunologic aspects of isocyanate asthma: IL-1 beta, IL-3, IL-4, sIL2R, and sICAM-1

This pilot study investigated serum levels of cytokines and soluble receptors during five positive and five negative isocyanate inhalational challenges. Serum was obtained from 10 individuals with symptoms compatible with isocyanate asthma before isocyanate challenge and the day following their maximal change in pulmonary function after isocyanate challenge. Serum levels of interleukin 1 beta, interleukin 3, interleukin 4, soluble interleukin 2 receptor, and soluble intercellular adhesion molecule 1 were measured and compared. Interleukin 1 beta, interleukin 3, and interleukin 4 were not detected. The mean soluble interleukin 2 receptor and soluble intercellular adhesion molecule 1 levels were not statistically different before and after challenge or between groups. In summary, the cytokines studied are not detectable in peripheral blood during isocyanate inhalation challenge; soluble interleukin 2 receptor and soluble intercellular adhesion molecule 1 are both detectable but do not change significantly after a positive isocyanate challenge.

Influence of beclomethasone and salmeterol on the perception of methacholine-induced bronchoconstriction

BACKGROUND

Patient evaluation of asthma severity and medication needs is mostly based on respiratory symptoms and may be influenced by changes in perception of bronchoconstriction-induced sensations. However, the influence of asthma medication on the ability to perceive symptoms is still to be documented. This study evaluated the effects of short-term and regular use of salmeterol on the perception of methacholine-induced bronchoconstriction (MIB) in subjects with mild asthma, using inhaled salbutamol on an "as required" basis (n=15), and in subjects with moderate asthma, using daily inhaled beclomethasone (mean daily dose, 640 microg; n=15) in addition to salbutamol to control their asthma.

METHODS

Methacholine challenges (MC) were performed at entry into the study, and then before, 1, and 12 h following inhalation of 50 microg of salmeterol or a placebo, after a 15-day baseline period; and after 4 weeks of twice daily use of those treatments. The measurements were then repeated with the alternate treatment after a 15-day washout period. Finally, a last MC was performed after another 15-day washout period. For each MC, the perception score of bronchoconstriction-associated breathlessness at 20% fall in FEV1 (PS20) was evaluated on a modified Borg scale from 0 to 10.

RESULTS

Subjects using regular beclomethasone had a higher baseline PS20 than those using only salbutamol (means: 3.06 0.06 and 2.01+/-0.07, p=0.0001). Short- and long-term use of salmeterol did not change significantly the PS20 compared with placebo (p>0.05) in either group (with or without corticosteroid). Although there were some intraindividual variations, mean PS20 did not vary significantly throughout the study.

CONCLUSION

These observations show that the perception of bronchoconstriction-associated breathlessness is not influenced by regular use of salmeterol. Patients using inhaled corticosteroids show a greater perception of MIB.

Follow-up of occupational asthma after removal from or diminution of exposure to the responsible agent: relevance of the length of the interval from cessation of exposure

STUDY OBJECTIVE

We set the hypothesis that follow-up surveys of occupational asthma (OA) could now show better improvement in the asthmatic condition because of a more prolonged interval since removal from exposure than in previously reported studies.

PATIENTS/METHODS

Ninety-nine subjects with OA were assessed and were separated into two groups according to the duration of cessation of exposure: (1) group removed for > or = 5 years: 48 subjects studied 8.9+/-2.2 years after cessation of exposure; (2) group removed for <5 years: 51 subjects with OA, comparable in terms of history and functional results at time of diagnosis, with a time lapse from last exposure of 3.1+/-1.2 years. On the follow-up visit, questionnaires including information on the current and previous use of inhaled steroids, spirometry, and methacholine tests were administered and results were compared with those obtained at the time of diagnosis.

RESULTS

At the follow-up visit, no significant changes in spirometry were observed in the two groups. However, a significant improvement in provocative concentration of methacholine causing a 20% fall in FEV1 (PC20) from a mean value of 1.5 to 3.7 mg/mL was documented (p<0.001). The proportion of subjects having normal PC20 at the follow-up visit was significantly higher in the group removed from exposure for >5 years than in the group removed for < or = 5 years (16/33 vs 8/42; p=0.01). Stepwise logistic regression showed that follow-up PC20 could be predicted from baseline PC20 (p<0.001, odds ratio [OR]=4.1, 95% confidence interval [CI]=1.8 to 9.1), duration of exposure (p=0.04, OR=0.9, 95% CI=0.8 to 1.0), the interval since removal from exposure (p=0.002, OR=1.7, 95% CI=1.2 to 2.5), and the type of agent; subjects with OA due to high-molecular-weight agent showed a less favorable outcome (p=0.04, OR=0.2, 95% CI=0.03 to 1.0). Current and past treatments with inhaled steroids were not significant predictors.

CONCLUSION

Results obtained in the group of this study removed for >5 years show better prognostic figures than those reported in most previous studies. Comparison with the group removed for a shorter interval and the stepwise logistic regression analysis suggest that the longer duration of the interval from cessation of exposure appears to be a factor determining this difference.

Investigation of occupational asthma

Occupational asthma is one of the most frequent lung diseases related to work. It is defined as asthma causally and specifically related to exposure to airborne dusts, gases, vapours or fumes in the working environment. Because occupational asthma may cause long-lasting disability, it is important to identify affected workers correctly and to remove them as soon as possible from the sensitizing agent. Although history is the clue to the diagnosis, it is not sensitive nor specific enough, and the diagnosis should be confirmed by objective means. This article reviews the different steps (with their advantages and disadvantages) involved in making the diagnosis: history, confirmation of the diagnosis of asthma, work visit, skin tests and serology, monitoring of peak expiratory flows and nonallergic bronchial responsiveness. The gold standard remains specific inhalation challenges in the laboratory or at work.

Canadian Thoracic Society guidelines for occupational asthma

OBJECTIVE

To provide broad guidelines and principles to help primary care physicians, occupational physicians, allergists and respirologists with the recognition, diagnosis and management of patients with occupational asthma (OA).

OPTIONS

These guidelines are mainly directed towards OA induced by a workplace sensitizing agent. However, irritant-induced asthma and workplace aggravation of underlying asthma are also addressed, and some consideration is given to other differential diagnoses.

OUTCOMES

To enable the assessing physician to investigate patients with possible OA appropriately and to provide guidelines for appropriate early referral when specialized investigations are required. To provide an understanding of the appropriate management strategies following objective diagnosis.

EVIDENCE

The key diagnostic and management recommendations were based on a critical review of the literature and by specialist consensus meetings.

VALUES

Evidence was categorized as follows. Level 1: Evidence from at least one randomized, controlled trial. Level 2: Evidence from at least one well-designed clinical trial without randomization, from cohort or case-control analytical studies, preferably from more than one centre, from multiple time series or from dramatic results in uncontrolled experiments. Level 3: Evidence from the opinions of respected authorities based on clinical experience, descriptive studies or reports of expert committees. Evidence was further subdivided as follows: A. Good evidence to support a recommendation for use; B. Moderate evidence to support a recommendation for use; C. Poor evidence to support a recommendation for or against use; D. Moderate evidence to support a recommendation against use; E. Good evidence to support a recommendation against use.

BENEFITS, HARM AND COSTS

The medical and socioeconomic risks and benefits of an incorrect diagnosis of OA and of failure to diagnose true OA were considered in the recommendations.

VALIDATION

The document has been reviewed and endorsed by the Canadian Thoracic Society, the Canadian Society of Allergy and Clinical Immunology, and The College of Family Physicians of Canada.

CONCLUSIONS

There is good evidence for rapid investigation and objective categorization of presented symptoms into OA, aggravation of underlying asthma, unrelated asthma or other diagnoses. OA should be suspected in all adult onset asthmatics whose asthma begins or worsens while they are working. Investigations should be directed to an objective assessment of asthma and then to an assessment of the work relationship, using a combination of investigations as feasible, which may include immunological tests, pulmonary function assessed during work periods and away from work, and specific challenge tests. Early specialist referral is recommended for diagnosis. Management strategies include general asthma management in addition to measures to avoid further exposure to a relevant workplace sensitizer. Compensation issues and other workers at risk of developing OA also need to be considered when the diagnosis is made.

Tolerance to the protective effects of salmeterol on methacholine-induced bronchoconstriction: influence of inhaled corticosteroids

Long-acting beta2-adrenoceptor agonists such as salmeterol reduce airway responsiveness for at least 12 h, but this effect seems to decrease with regular use. We evaluated the time-course of the protective effects of salmeterol on methacholine-induced bronchoconstriction, its modulation by inhaled corticosteroids (ICS) and its influence on asthma control. Thirty two subjects (13 males and 19 females) with mild to moderate stable asthma were divided into two groups according to their medication needs: bronchodilators (BD) alone (n=16) or with ICS (n=16). After a 2 week run-in period, a double-blind crossover study was conducted. Subjects from both groups received salmeterol 50 microg b.i.d. or a placebo for 4 weeks each in random order, separated by a 2 week washout period. The provocative concentration of methacholine causing a 20% fall in forced expiratory volume in one second (PC20) was measured before and after each treatment period, 1 h prior to inhalation of salmeterol or placebo and 1 and 12 h after. Baseline forced expiratory volume in one second (FEV1) increased significantly after salmeterol, both after the first dose and at 4 weeks (BD group: 19 and 17%; ICS: 22 and 13%). On the first day of administration, salmeterol provided significant protection in both groups up to 12 h with a PC20 before and 1 and 12 h postdose of 2.2, 21.7 and 12.4, mg x mL(-1), respectively, in the BD group and 2.1, 11.6 and 55 mg x mL(-1), respectively, in the ICS group. After 4 weeks, this effect was significantly attenuated in both groups with a PC20 before, 1 and 12 h postdose of 3.3, 10.9 and 7.1 mg x mL(-1), respectively, in the BD group and 2.1, 5.0 and 2.3 mg x mL(-1), respectively, in the ICS group. This loss of protective effect was of similar magnitude in both groups. Respiratory symptoms, rescue beta2-agonist use and baseline FEV1 did not change significantly throughout the study in both groups. In conclusion, the bronchoprotective effect of salmeterol decreased with regular use both 1 and 12 h postdose; inhaled corticosteroids did not prevent this reduction. However, the development of tolerance was not associated with loss of asthma control.

Compliance with peak expiratory flow monitoring in home management of asthma

BACKGROUND

The recent consensus reports on asthma management emphasize the importance of using peak flowmeters to accurately assess the degree of airflow obstruction. However, the optimal way to use those devices has not yet been determined.

OBJECTIVES

To assess compliance with peak expiratory flow (PEF) measurements in the long-term management of asthma, and identify the characteristics of patients with poor compliance.

SETTING

Asthma clinics from three tertiary-care hospitals.

DESIGN

A descriptive and prospective study of 1-year duration.

PATIENTS

Twenty-six patients with moderate to severe asthma taking part in an asthma education program.

MAIN OUTCOME MEASURES

Patients were asked to measure morning and evening PEF using an electronic peak flowmeter with a 3-month memory; they were unaware that PEF values were being recorded by this device.

RESULTS

Compliance with PEF measurements was relatively good during the first month (63% of the measurements done) but even with regular reinforcement, fell to 50% at 6 months and to 33% at 12 months. Right from the beginning, 8 of 26 subjects (30%) never or almost never (<5% of the readings done) measured PEF, with seven of these subjects writing fabricated results in their diaries most of the time. At 12 months, 60% of the subjects were measuring PEF <25% of the time, and most of them continued writing fabricated PEF values in their diaries. None of the subjects' characteristics helped us to identify those who had poor compliance with these measurements.

CONCLUSIONS

While short-term compliance with PEF measurements is fairly good, most patients with moderate to severe asthma are not interested in measuring PEF twice daily over a prolonged period. In the current management of asthma, PEF measurement devices can be suggested to those showing a strong personal interest in using them, but should be limited to short periods of time. Furthermore, this study outlines the usefulness of electronic peak flowmeters when doing clinical research where PEF improvement is an important outcome.

Can reactive airways dysfunction syndrome (RADS) transform into occupational asthma due to "sensitisation" to isocyanates?

The case history is described of a worker who presented with a history suggestive of reactive airways dysfunction syndrome which occurred after an acute high level inhalation of diphenylmethane diisocyanate. Further exposure at work, at a time when concentrations of isocyanates were no longer "irritant", suggested occupational asthma; this diagnosis was confirmed by a specific inhalation challenge test.

Prevalence and intensity of rhinoconjunctivitis in subjects with occupational asthma

Subjects with occupational asthma may also report symptoms of rhinoconjunctivitis. The aims of this study were: 1) to assess the prevalence of rhinoconjunctivitis in association with occupational asthma, and the severity of rhinoconjunctivitis according to the type of agent (high (HMW) and low (LMW) molecular weight agents) causing occupational asthma; and 2) to evaluate the timing of occurrence of symptoms of rhinoconjunctivitis in relation to those of occupational asthma. A questionnaire on symptoms of rhinoconjunctivitis and its timing in relation to the development of chest symptoms was prospectively addressed to 143 subjects consecutively referred to an occupational asthma clinic. Objective testing through specific inhalation challenges confirmed the diagnosis of occupational asthma in 40 subjects. Symptoms of rhinitis were reported at some time by 37 of the 40 subjects (92%), and of conjunctivitis by 29 of the 40 subjects (72%). The prevalence of symptoms was not different for HMW and LMW agents, although rhinitis was more intense for HMW (19 out of 24 subjects with three or more of the following symptoms: runny nose, itchy nose, nasal blockage, and sneezing) than for LMW (5 out of 14 subjects) (p<0.01). There were significantly fewer subjects with occupational asthma due to LMW agents, with rhinitis appearing before asthma (p=0.03). Figures for conjunctivitis showed a similar trend, but did not reach statistical significance. In conclusion, symptoms of rhinoconjunctivitis are often associated with occupational asthma. Rhinitis is less pronounced in the case of low molecular weight agents, but more often appears before occupational asthma in the case of high molecular weight agents.

Bronchial subepithelial fibrosis correlates with airway responsiveness to methacholine

OBJECTIVES

To evaluate the relationships between airway subepithelial collagen deposition and epithelial desquamation with airflow obstruction and hyperresponsiveness in different types of asthma and other respiratory conditions such as chronic cough and allergic rhinitis.

DESIGN AND PARTICIPANTS

We compared the histopathologic features observed on bronchial biopsy specimens obtained from 80 subjects: 38 with different types of asthma, 19 with chronic cough, 13 with allergic rhinitis, and 10 normal control subjects. Each subject had a questionnaire on respiratory symptoms and medication needs, measurements of expiratory flows and methacholine responsiveness, allergy skin prick tests, and a bronchoscopy with bronchial biopsies. None of the subjects studied used bronchial anti-inflammatory agents.

RESULTS

Different degrees of bronchial subepithelial fibrosis were present in asthmatic subjects, the most intense being observed in occupational asthma; a subepithelial deposition of collagen was also found in subjects with allergic rhinitis, although it was less intense than in asthma and irregularly distributed under the basement membrane. On global analysis, we found a significant correlation between individual provocative concentration of methacholine inducing a 20% fall in FEV1 (PC20) and subepithelial fibrosis intensity (rs=-0.70, p<0.001). The degree of epithelial desquamation was correlated with that of subepithelial fibrosis (rs=0.36, p=0.02) in subjects with normal airway responsiveness, but it was not correlated with the PC20 (rs=0.10, p>0.05). Neither the degree of subepithelial fibrosis nor epithelial desquamation was correlated with the FEV1.

CONCLUSION

These results suggest that structural airway changes such as subepithelial collagen deposition may be significant determinants or markers of a process that results in airway hyperresponsiveness.

Influence on asthma morbidity of asthma education programs based on self-management plans following treatment optimization

The objective of this study was to evaluate the effectiveness of an asthma education program on morbidity, knowledge, and compliance with inhaled corticosteroid treatment using a prospective, randomized, controlled, one-year-before/one-year-after protocol. After rigorous optimization of asthma therapy under the care of respirologists, patients were assigned to one of three groups: Group C (control group: no formal education), Group P (education and action plan based on peak-flow monitoring), and Group S (education with action plan based on monitoring of asthma symptoms). A total of 188 subjects with moderate to severe asthma were enrolled and 149 completed the study. Asthma morbidity decreased significantly in all groups (p = 0.001). Mean values one-year-before/one-year-after in Groups C, P, and S were: unscheduled medical visits, 2.4/0.8, 2.3/0.7, and 1.9/ 0.7; hospitalizations, 0.21/0.04, 0.24/0.04, and 0.40/0.09; oral steroid treatments; 1.3/0.5, 1.2/0.7, and 1.3/0.9; absenteeism from work/school, 9.6/5.2, 8.8/2.2, and 6.3/2.9. Between-group differences did not reach statistical significance (p > 0.05). Asthma knowledge increased in both educated groups compared with the control group (p < 0.001) as did short-term compliance with inhaled corticosteroids. These results confirm that treatment optimization coupled with sustained high quality care in motivated patients can lead to a significant decrease in asthma morbidity. In such clinical settings, structured asthma education significantly improved short-term compliance with treatment and knowledge about asthma, although it could not add extra benefit with regard to morbidity. Nevertheless, this study does not refute the potential benefit of educational interventions aimed at improving asthma-related morbidity over a longer time period or in patients with less optimal care or with high-risk factors.

Alexithymia and impoverished dream recall in asthmatic patients: evidence from self-report measures

Early clinical impressions that alexithymia is associated with diminished dream recall have been supported by more recent research. The present study was designed to examine this association using self-report measures and a carefully screened clinical population. Thirty-three male and 43 female asthmatics from an outpatient clinic were administered the Toronto Alexithymia Scale, the Eysenck Personality Questionnaire, and a questionnaire concerning retrospective recall of dreams and nightmares. Multiple regression analyses revealed that, among men, dream recall was negatively related to alexithymia, especially to the TAS analytical mode of thinking subscale, independent of age and neuroticism. Among women, dream and nightmare recall were positively correlated with neuroticism. These results are consistent with early clinical observations of pensée opératoire, with some research findings, and with the notion that dream recall may be differentially associated with components of alexithymia in men and women patients.

Occupational asthma caused by aromatic herbs

We describe a subject with occupational asthma caused by several aromatic herbs: thyme, rosemary, bay leaf, and garlic. The diagnosis was confirmed by several inhalation challenges in the laboratory. Although immediate skin reactivity was demonstrated to the herbs the subject reacted to by inhalation, RAST showed that garlic was the most potent allergen by weight, the other herbs showing less reactivity. These aromatic herbs, bay leaf, thyme, and rosemary, should be included among agents causing occupational asthma in the food industry.

Isolated late asthmatic reaction after exposure to a high-molecular-weight occupational agent, subtilisin

High-molecular-weight agents generally induce immediate asthmatic reactions. We report the case of a subject who experienced a reaction that started after the first hour following exposure to subtilisin, a high-molecular-weight occupational agent. Any occurrence of immediate reaction was ruled out by measuring both FEV1 and lung volumes every 10 min in the first hour. This reaction was IgE-mediated as shown by immediate skin reactivity and increased specific IgE levels.

Outcome of specific bronchial responsiveness to occupational agents after removal from exposure

A decrease in specific bronchial responsiveness (SBR) could occur after removal from exposure to an agent causing occupational asthma as a result of loss of immunologic and/or nonspecific bronchial reactivity (NSBR). We studied 15 subjects with occupational asthma (eight to a high- and seven to a low-molecular-weight agent, isocyanate in all instances), proved by specific inhalation challenges (SIC) done 2 yr or more before. Subjects were reexposed in the same way as in the initial SIC: for subjects who did not react, the exposure was increased until either an asthmatic reaction occurred or a maximum of 2 h was reached. NSBR was assessed before and after SIC. Subjects had a decrease in their SBR if the total dose of agent necessary to induce asthmatic reaction was greater by twofold compared with the initial SIC. There was a significant improvement in NSBR in seven of 15 subjects. Nine of 15 subjects (60%) had a decrease in their SBR. Only one had a complete loss of SBR. Changes in NSBR, molecular weight of the offending agent, decrease of antibody level against offending agents, or duration of exposure at work did not explain the decrease in SBR. We conclude that after removal from exposure to the offending agent a majority of subjects (60%) show a decrease but a persistence of SBR to high- and low-molecular-weight agents.

Closed-circuit apparatus for specific inhalation challenges with an occupational agent, formaldehyde, in vapor form

Specific inhalation challenges are an important tool for confirming occupational asthma. In recent years, we have described two closed-circuit apparatuses that allow exposure to stable and controlled concentrations of particles and isocyanate gases. More recently, we developed a similar apparatus that generates chemicals in vapor form. The aim of this work is to describe its performance in the specific case of formaldehyde. This instrument is made of four parts: a generator as such, an exposure chamber, a monitor, and an automated regulatory system. This apparatus was assessed in four subjects suspected of having formaldehyde-induced asthma or alveolitis. The concentrations of formaldehyde were increased from 0.5 to 1 mg/m3 to 3 mg/m3 keeping the concentration at a value of 3 mg/m3 or less (threshold limit value). The dispersion of obtained values by comparison with the median data (6 values) was as follows: maximum value, 12 to 84%; minimum value, 20 to 58%; interquartile range, 0.13 to 0.9 mg/m3. We observed that target concentrations took a few minutes to be reached, but, once they were obtained, delivered concentrations were stable. The new vapor-delivery apparatus allows us to obtain concentrations of formaldehyde that are close to target concentrations with an acceptable dispersion of values around target concentration. Its use should be extended to other chemicals besides formaldehyde.

Compliance with and accuracy of daily self-assessment of peak expiratory flows (PEF) in asthmatic subjects over a three month period

Serial peak expiratory flow (PEF) assessment has been proposed in the clinical evaluation of asthma. In subjects attending the asthma clinic of a tertiary care hospital, we wanted to assess: 1) compliance in performing PEF; and 2) accuracy of a PEF-diary. Twenty adult asthmatic subjects, all using inhaled steroids, were asked to assess their PEF in the morning and evening with a VMX instrument (Clement Clarke Int., Colombus, OH, USA). This instrument, which incorporates a standard mini-Wright peak flow meter, stores PEF data on a computer chip. Subjects were not informed that the values were being stored. The mean duration of PEF monitoring was 89 days (range 44-131 days). For the total of 20 subjects, it was estimated that 3,482 values should have been written down and stored on the VMX computer chip. Whilst 1,897 values (54%) were written down, only 1,533 (44%) were stored, 425 values being invented. Morning and evening values were stored on 34% of days; and values were stored at least once a day on 55% of days. The values written down corresponded precisely to stored values 90% of the time, and were within +/- 20 L 94% of the time. We conclude that: 1) compliance with daily peak expiratory flow assessments is generally poor in chronic stable asthmatic subjects assessed on two visits separated by a 3 month period; and 2) a substantial percentage of values (22%) is invented. The unsatisfactory compliance with peak expiratory flow monitoring in this group of asthmatics on inhaled steroids underlines the need for similar studies on peak expiratory flow monitoring as part of an action treatment plan, and in more severe and brittle asthmatics.