Late asthmatic reactions to occupational sensitizing agents: frequency of changes in nonspecific bronchial responsiveness and of response to inhaled beta 2-adrenergic agent

Inhalation Challenge Tests in Occupational Asthma: Why Are Multiple Tests Needed?

Occupational and environmental lung diseases are on the rise because of the widespread use of various toxic agents in industry. Asthma etiopathogenesis is unclear because of exposure to high and low molecular agents in workplaces. Approximately 15-25% of asthma in adults is reported to be related to occupational exposure. The prevalence of occupational asthma (OA) is predicted to be high. The difficulties in diagnosing OA results in inadequate treatment, permanent airway damage, and medicolegal and social problems. As with other occupational diseases, it is necessary to demonstrate a direct causal relationship between the suspected agent and OA. Spirometry, peak expiratory flow rate, and/or non-specific bronchial hyperresponsiveness are frequently used to show airway hyperresponsiveness at the workplace and away from work. However, there are some controversies about the specificity and sensitivity of these test methods. Furthermore, these tests do not identify the exposure agent, which could be the causative agent. Specific inhalation challenge (SIC) tests that demonstrate the direct causal relationship are currently the gold standard. However, their positive and negative predictive values have not yet been established; therefore, many low molecular weight agents could cause late or atypical reactions. Therefore, a negative SIC test cannot exclude the disease. This review describes the procedures for the SIC test and discusses the importance of using the combined test methods with the SIC test.

Long-term socioprofessional and psychological status in workers investigated for occupational asthma in quebec

OBJECTIVE

To compare the long-term status of workers with occupational asthma (OA) with those of subjects with work-exacerbated asthma (WEA) and nonasthmatic (NA) workers.

METHODS

We contacted 179 subjects investigated for suspected OA at Hôpital du Sacré-Coeur de Montréal, Montreal, Quebec, Canada, from 1997 to 2007. Participants completed questionnaires on psychological and functional status, followed by a telephone interview about socioprofessional outcomes and health care utilization.

RESULTS

The OA workers are more likely to have been removed from the workplace than the WEA workers. The health-related quality of life of all workers was still impaired. A high prevalence of psychiatric disorders was found among OA and WEA workers. Compared with WEA and OA workers, the NA group showed a higher rate of physician consultations for all causes.

CONCLUSIONS

Regardless of the diagnosis they received, these workers need to benefit from psychosocial support in the period after investigation for suspicion of OA.

Inhalation challenges with occupational agents: threshold duration of exposure

OBJECTIVES

The aim of this study was to characterize the threshold duration of exposure needed to elicit an asthmatic reaction during specific inhalation challenges (SIC) with various occupational agents and to determine the duration of exposure that should be completed before the test can be considered negative.

METHODS

This retrospective study analysed the cumulative duration of challenge exposure that was required to elicit a ≥20% fall in forced expiratory volume in one second in 335 consecutive subjects with a positive SIC.

RESULTS

The threshold duration of challenge exposure required to induce an asthmatic reaction was ≤60 min in 179 (53%) subjects, between 61 and 120 min in 74 (22%) subjects, and longer than 120 min in 82 (25%) subjects. The multivariate linear regression analysis showed that a longer duration of exposure was associated with exposure to low-molecular-weight agents (p < 0.001), a higher level of baseline non-specific bronchial hyperresponsiveness to histamine (p = 0.015), increasing age (p = 0.011), and a shorter duration of asthma symptoms at work (p = 0.060).

CONCLUSIONS

This study demonstrates that the sensitivity of SICs for diagnosing OA is highly dependent upon the duration of the challenge exposure. These data may provide useful guidance for improving the reliability of SICs performed with realistic methods of exposure.

Distinct temporal patterns of immediate asthmatic reactions due to high- and low-molecular-weight agents

BACKGROUND

Exposure to occupational agents can cause immediate asthmatic reactions.

OBJECTIVE

It can be hypothesized that the pattern of immediate reactions is different for high (HMW)- and low-molecular-weight (LMW) agents. To test this, we studied the temporal features of reactions in workers who underwent specific inhalation challenges for possible occupational asthma.

METHODS

We examined 467 immediate reactions due to HMW (n = 248, 53%) and LWW (n = 219, 47%) agents in regards to timing of the maximum reaction and recovery.

RESULTS

The median duration of exposure to elicit significant immediate reactions was comparable for HMW and LMW agents (15 min). The median maximum fall in FEV (1) occurred after 20 min for LMW by comparison with 10 min for HMW agents (P < 0.001). The median timing of recovery of FEV (1) to 10% baseline was shorter for HMW (60 min) than for LMW (90 min) agents (P < 0.01), and significantly more subjects recovered to 10% baseline (89.5%) for HMW than for LMW agents (72.6%) (P < 0.001). Confounding variables such as age, atopy, baseline airway calibre and the maximum fall in FEV (1) at the time of the immediate reaction did not alter the significant effect of the nature of the agent per se. Immediate reactions were followed by a late asthmatic reaction more often in the case of LMW (37.3%) than HMW (26.2%) agents (P < 0.05). Significant changes in non-specific bronchial responsiveness were significantly (P = 0.02) more frequent after reactions to LMW (31.9%) than to HMW (21.4%) agents. We found similar trends by comparing reactions to flour (n = 113), the principal cause of reactions to HMW agents, and diisocyanates (n = 111), the principal LMW agent.

CONCLUSIONS AND CLINICAL RELEVANCE

This study shows distinct patterns for immediate reactions due to occupational agents. These results can provide useful guidelines for performing specific inhalation challenges and improve the safety of the procedure.

Definitions and classification of work-related asthma

The workplace can trigger or induce asthma and cause the onset of different types of work-related asthma (WRA). Based on current knowledge of clinical features, pathophysiologic mechanisms, and evidence supporting a causal relationship, the following conditions should be distinguished in the spectrum of WRA: (1) immunologic occupational asthma (OA), (2) nonimmunologic OA, (3) work-exacerbated asthma, and (4) variant syndromes, including eosinophilic bronchitis, potroom asthma, and asthmalike disorders caused by organic dusts. The rationale, issues, and controversies relating to this approach are critically reviewed to stimulate the development of a consensus on operational definitions of the various phenotypes of WRA.

Persistent specific bronchial reactivity to occupational agents in workers with normal nonspecific bronchial reactivity

Specific bronchial reactivity (SBR) to common inhalants is related to the degree of nonspecific bronchial reactivity (NSBR) and to specific allergen sensitivity. We investigated 16 workers with normal NSBR who had been previously diagnosed with occupational asthma caused by high-molecular-weight agents. The agents were flour in seven workers, psyllium in five, and guar gum in four. The subjects had been removed from exposure to these agents for a mean of 5.7 (+/- 4.0 SD) yr, no longer showed evidence of persisting asthma, and had a normal lung function. In the present study, the workers were reexposed to the sensitizing agent by specific inhalation challenges, in the same way they were as at the time of the diagnosis, to assess their current SBR to the sensitizer. SBR was estimated as the duration of exposure that induced a 20% decrease in FEV(1). Eleven of the 16 subjects had an asthmatic reaction at the time of the study; the duration of exposure necessary to induce the asthmatic reaction was the same as that needed at the time of diagnosis (3.55 +/- 0.5 min and 4.2 +/- 0.7 min, respectively, p = 0.8). The decrease in specific IgE levels between the two events was much greater in the subjects who failed to react to the second challenge test (from 24.2 +/- 37.5% to 3.0 +/- 16.9% binding) than in those who reacted on both occasions (from 31.2 +/- 27.0% to 21.6 +/- 36.7% binding); however, in both groups the change was significant (p = 0.05 and 0.04, respectively). We conclude that SBR to high-molecular-weight agents persists in most cases despite a normalization of NSBR, and that this persistence is associated with a persistence of specific immunization to the agent.

Increase in non-specific bronchial hyperresponsiveness without specific response to isocyanate in isocyanate-induced asthma: a pilot study

Increased non-specific bronchial hyperresponsiveness (BHR) has been reported after positive reaction to isocyanates in patients with isocyanate-sensitive asthma. The increased responsiveness may, however, also precede the asthma attack. We therefore compared non-specific BHR to a cholinergic agent before and after exposure to toluene-diisocyanate (TDI) that induced no asthma symptoms in 11 workers with isocyanate-related asthma. Patients were exposed for 3 consecutive days to progressively increasing doses of TDI (5, 10, and 20 ppb min-1 for 20 min) in an exposure chamber with continuous TDI monitoring. No immediate nor late asthmatic bronchial reaction was observed in any patient after any dose of TDI during or after challenge. A significant increase in non-specific BHR was noted 24 h after the last dose of TDI challenge, however. This increase was at least one doubling dose for seven of 11 patients. In conclusion, our study shows that, in patients with isocyanate-induced asthma, exposure to TDI induces a slight but significant increase in non-specific BHR in the absence of any immediate or late bronchial response to isocyanate. This result, which requires further confirmation, may justify a proposal to measure non-specific BHR, even after a negative specific inhalation test to TDI, as an additional diagnostic element for TDI-induced occupational asthma, to help lower the percentage of the undetected occupational asthma cases.

Rapid reversibility of the allergen-induced pulmonary late-phase reaction by an intravenous beta2-agonist

This study was performed to determine the degree to which beta2-adrenergic receptor agonists can reverse the allergen-induced late reduction in lung function. On two occasions, seven asthmatic subjects were administered terbutaline or its vehicle by intravenous infusion 7 h after inhaled allergen, at which point the forced expiratory volume in 1 s was 57% of baseline. On another occasion, terbutaline was infused at baseline to determine maximal attainable bronchodilation. After allergen challenge, terbutaline rapidly improved lung function. At the end of terbutaline infusion, the forced expiratory volume in 1 s reached 100 +/- 1.3% of baseline and 84.2 +/- 4.3% of maximal attainable value, but the bronchodilating effect of the beta-agonist did not plateau. The values for forced vital capacity were 102 +/- 1.3% of baseline and 95.1 +/- 3% of maximal attainable value. The kinetics of the terbutaline effect, when it was infused at baseline, were similar to those in the late phase. Because the late-phase reduction in lung function is rapidly reversible by beta2-adrenergic agonists, we conclude that it is caused mainly by bronchial smooth muscle spasm.

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.

Increase in non-specific bronchial hyperresponsiveness as an early marker of bronchial response to occupational agents during specific inhalation challenges

BACKGROUND

Specific bronchial reactivity to occupational agents may decline after exposure in the workplace ceases leading to falsely negative specific inhalation challenges. A study was carried out to assess prospectively whether increases in nonspecific bronchial hyperresponsiveness could be useful in detecting the bronchial response to occupational agents during specific inhalation challenges.

METHODS

Specific inhalation challenges were performed in 66 subjects with possible occupational asthma due to various agents. After a control day the subjects were challenged with the suspected agent for up to two hours on the first test day. Those subjects who did not show an asthmatic reaction were rechallenged on the next day for 2-3 hours. The provocative concentration of histamine causing a 20% fall (PC20) in the forced expiratory volume in one second (FEV1) was assessed at the end of the control day as well as six hours after each challenge that did not cause a > or = 20% fall in FEV1. The subjects who had a significant (> or = 3.1-fold) reduction in PC20 value at the end of the second challenge day were requested to perform additional specific inhalation challenges.

RESULTS

The first test day elicited an asthmatic reaction in 25 subjects. Of the other 41 subjects five (12%, 95% confidence interval (CI) 4% to 26%) exhibited a > or = 3.1-fold fall in the PC20 value after the inhalation challenge and developed an asthmatic reaction during the second (n = 3) or third (n = 2) challenge exposure. The offending agents included persulphate (n = 1), wood dust (n = 2), isocyanate (n = 1), or amoxycillin (n = 1). These five subjects had left their workplace for a longer period (mean (SD) 21 (14) months) than those who reacted after the first specific inhalation challenge (8 (11) months).

CONCLUSIONS

The increase in non-specific bronchial hyperresponsiveness after a specific inhalation challenge can be an early and sensitive marker of bronchial response to occupational agents, especially in subjects removed from workplace exposure for a long time. Non-specific bronchial hyperresponsiveness should be systematically assessed after specific inhalation challenges in the absence of changes in airway calibre.

Occupational asthma caused by oak wood dust

Three cases of occupational asthma caused by oak wood dust are presented. The diagnosis was confirmed by specific inhalation challenges, which induced a dual asthmatic reaction in two subjects and an atypical prolonged immediate reaction in one subject.

Occupational asthma due to gas metal arc welding on mild steel

Occupational asthma has been documented in electric arc welders exposed to manual metal arc welding on stainless steel. A subject is described who developed late and dual asthmatic reactions after occupational-type challenge exposure to gas metal arc welding on uncoated mild steel.

Reversibility of the allergen-provoked late asthmatic response by an inhaled beta 2-adrenoceptor agonist

There is uncertainty about the relative contributions of bronchial smooth muscle contraction, mucosal oedema and mucus plugging to airflow obstruction in the allergen-induced late asthmatic response (LAR). We systematically studied the ability of the inhaled beta 2-agonist salbutamol to reverse the LAR in eight subjects after allergen bronchoprovocation. Salbutamol reversed the LAR by restoring FEV1 to a level similar to the initial value measured at the same time of day (18.00 h) on the previous evening. For the eight subjects studied, this initial FEV1 value, measured after abstaining from beta-agonists for 8 h, was a mean +/- SEM 90.7 +/- 5.6% of predicted, which suggests further bronchodilation may have been possible at this time. We then studied six of the eight subjects in an identical protocol with saline challenge substituted for allergen bronchoprovocation to answer the question whether further bronchodilation was possible at that time after salbutamol in the absence of an LAR. After salbutamol on the allergen challenge day the FEV1 for the six subjects was 84.1 +/- 7.0% of predicted, compared with 94.0 +/- 3.7% of predicted at the same point on the saline challenge day (P < 0.05). We conclude that, although the LAR may be effectively reversed by beta 2-agonists, there is evidence for some residual airway narrowing, presumably related to mucosal oedema, exudate and mucus plugging.

Modifications of PC20 and maximal degree of airway narrowing to methacholine after pollen season in pollen sensitive asthmatic patients

We examined the effect of cessation of exposure to pollen on non-specific airway responsiveness in 10 grass and/or parietaria pollen sensitive asthmatics. Three methacholine inhalation challenges were performed, the first during pollen season (seasonal period), the second 2 months after the end of season (short time after seasonal period), and the third 5 months after the end of season (long time after seasonal period). The dose-response curves to methacholine were characterized by the PC20 (provocative concentration of methacholine required to produce a 20% fall in FEV1) and maximal response plateau, if possible. A maximal response plateau on the dose-response curve was considered to be present if three or more data points for FEV1 fell within a 5% response range. The challenge was stopped when FEV1 dropped more than 50% or the highest concentration of methacholine (200 mg/ml) was reached. The geometric mean (range) methacholine PC20 increased from 1.08 (0.18-37.22) in the seasonal period to 4.67 (0.71-200) mg/ml during the long time after seasonal period (P < 0.01). On the other hand, in six subjects in whom it was possible to obtain a plateau on at least one challenge, the level of the maximal response decreased from (mean +/- s.e.m.) 44.1 +/- 4.9 in the seasonal period to 30 +/- 4.4 during the long time after seasonal period (P < 0.05). These results suggest that in pollen sensitive asthmatic patients, the cessation of exposure to pollen is associated with a reduction of non-specific bronchial responsiveness (PC20 and maximal degree of airway narrowing to methacholine).

Hypersensitivity pneumonitis-like reaction among workers exposed to diphenylmethane [correction to piphenylmethane] diisocyanate (MDI)

Isocyanates are well documented as a cause of occupational asthma. A hypersensitivity pneumonitis type of reaction has also been reported but only in a few isolated cases. We investigated nine subjects who complained of respiratory and general symptoms related to workplace exposure. All the subjects had worked in a plant where a resin based on diphenylmethane diisocyanate (MDI) is used in the manufacture of woodchip boards. They underwent inhalation challenges using the MDI resin for progressively increasing periods of time on separate days. In eight subjects, exposure to subirritant amounts of MDI induced a pattern of reaction consistent with hypersensitivity pneumonitis, i.e., significant falls in both FEV1 and FVC associated with a rise in body temperature (> 38 degrees C) and an increase in blood neutrophils (> +2,500/mm3). Bronchoalveolar lavage, performed in two subjects 24 h after the end of challenge exposure, revealed an increase in lymphocytes and neutrophils. Specific immunoglobulin G (IgG) and IgE antibodies to MDI human serum albumin (HSA) conjugates were present in all subjects. We conclude that the MDI resin caused an hypersensitivity pneumonitis type of reaction in at least eight (4.7%) of the 167 potentially exposed workers employed in the plant. These findings indicate that in some workplaces, a hypersensitivity pneumonitis type of reaction may be a more frequent consequence of isocyanate exposure than is usually thought.