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As part of our ongoing seminar series, the Centre of Excellence in Severe Asthma hosted Dr. Krystelle Godbout, for a webinar on “Occupational Asthma” on 29 August, 2016.
Presentation Summary:
Occupational asthma is asthma that is caused by or worsened by exposure in the workplace. Symptoms are caused by repeated exposures to specific triggers at work, which lead to disease pathology.
Occupational asthma can be subdivided into sensitiser-induced and irritant-induced subtypes. This seminar presentation focusses on sensitiser-induced occupational asthma, which represents approximately 90% of cases. A range of workplace exposures can act as sensitisers. Common sensitisers include flour, isocyanates, solvents, wood dust and chlorine.
Diagnosis of occupational asthma requires a combination of investigations. An initial confirmation of an asthma diagnosis is required. Relevant clinical history and questionnaires can suggest a diagnosis of occupational asthma. Lung function monitoring can demonstrate associations between symptoms and time at work. Further investigations may be useful to identify specific sensitisers (e.g. allergy testing). Specific inhalation challenge can demonstrate a causal relationship between sensitiser exposure and symptoms.
Management of occupational asthma includes pharmacological treatment based on asthma management guidelines and referral to a relevant workplace compensation board. Sensitiser avoidance is often necessary to improve symptoms, whereas reducing exposure to sensitisers can lead to a progressive worsening of disease.
Key Points:
- Work-related asthma can be subdivided into occupational asthma and work exacerbated asthma
- Work exacerbated asthma is pre-existing asthma that is worsened by exposure to triggers in the workplace
- Occupational asthma is asthma that is caused by or significantly worsened by exposure in the workplace environment, which would not exist otherwise
- Occupational asthma can be subdivided into sensitiser-induced and irritant-induced
- Sensitiser-induced occupational asthma accounts for 90% of cases, and is underdiagnosed
- Sensitisers are agents that induce a specific immunological response after repeated exposures
- Sites of sensitisation include respiratory, nasal, ocular or cutaneous routes
- Sensitisers are subdivided into 2 types, high molecular weight (e.g. proteins, such as flour or animal dander) and low molecular weight (e.g. chemicals, such as diisocyanates and wood dust)
- High molecular weight sensitisers stimulate allergic immune responses, which typically include Type-2 and eosinophilic airway inflammation
- Responses to low molecular weight sensitisers are less understood, but can contribute to eosinophilic or neutrophilic airway inflammation
- Risk factors for developing occupational asthma include pre-existing atopy, genetic predisposition, smoking status, occupational rhinitis, the level of sensitiser exposure and the type of sensitiser
- Investigations to diagnose occupational asthma include questionnaires, allergy testing, peak expiratory flow (PEF) monitoring at work and away from work, repeated measurement of bronchial hyperreactivity or inflammation at work and away from work, specific inhalation challenge and workplace challenge
- Confirmation of a diagnosis of asthma is required
- Questionnaires should assess the type of work and sensitiser exposure, use of respiratory protection, presence of symptoms in colleagues, latency of symptoms, whether improvements occur on weekends/holidays and associated symptoms
- Material Safety Data Sheets (MSDS) provide information on the ingredients found in workplace chemicals, which can be useful to identify potential sensitisers
- Bronchial provocation tests can be normal, if the patient is not currently exposed in the workplace
- Negative methacholine challenge can effectively rule out occupational asthma in symptomatic patients (note: hypertonic saline challenge is less sensitive)
- Specific allergy testing is available for most high molecular weight sensitisers, although specificity is quite low (while a positive result demonstrates sensitisation, it does not necessarily indicate occupational asthma)
- Peak expiratory flow (PEF) monitoring (4 measurements / day) including periods at work and off work is commonly used to document associations between lung function and time at work
- Serial measurements of bronchial hyperreactivity or airway inflammation, during periods of work versus off-work periods (after holiday) can improve diagnosis specificity
- Specific inhalation challenge can be useful if other investigations are equivocal or negative for occupational asthma, or identification of a specific sensitiser is necessary
- Workplace challenge may be useful if no causal agent is identified, the exposure cannot be recreated in the laboratory or a specific inhalation challenge is negative but occupational asthma is considered likely
- Management includes treatment with standard asthma medications (e.g. ICS + LABA), referral to a relevant workplace compensation board and avoidance of sensitiser exposure
About Dr. Krystelle Godbout:
Dr. Krystelle Godbout is a pulmonologist from Quebec, Canada with an interest in severe asthma and occupational asthma. Upon completion of her respiratory training, she spent a year at the Hôpital du Sacré-Coeur (Montreal, Canada), training in occupational asthma.
At the time of this seminar, she was completing a one-year fellowship in severe asthma at the Hunter Medical Research Institute (HMRI) and John Hunter Hospital, Newcastle.
