Chapter 34

• • Typical symptoms of asthma, bronchodilator reversible expiratory airflow limitation, and airway hyperresponsiveness.
• • Symptoms due to asthma rather than an alternative diagnosis.
• • Onset after entering the workplace.
• • Directly attributable to exposures in the workplace.
• • Specific immunoglobulin E (IgE) formation or positive skin testing may only represent allergic sensitization.
• • Specific inhalational challenge may confirm the diagnosis.

Occupational asthma can be defined as new-onset asthma that is directly attributable to one or more exposures in the workplace and not to exposures encountered outside the workplace. A diagnosis of occupational asthma can be made only after a diagnosis of asthma has been established and after the onset of asthma has been clearly related to the workplace. In addition to providing an environment in which asthma may be induced, the workplace can provide a number of exposures that exacerbate preexisting asthma and it is important to distinguish between preexisting asthma that is exacerbated by work and true occupational asthma.

Occupational asthma is the most prevalent occupational lung disease in the industrialized world. Studies in Canada and the United Kingdom indicate that occupational asthma accounts for up to approximately 50% of all cases of work-related lung disease, and a significant proportion of patients who are disabled due to asthma relate their disability to occupational asthma. United States Social Security Administration disability data indicate that approximately 15–20% of those individuals who are disabled due to asthma have occupational asthma.

Over 200 agents have been identified as causes of occupational asthma. Isocyanates are commonly implicated, as are wood dusts, anhydrides, dyes, metals, cereals, and latex. Common causes of occupational asthma in at-risk workers are listed in Table 34–1. Risk for occupational asthma appears to be directly related to the type of workplace exposures that an individual sustains, although traditional risk factors for asthma such as atopy are also considered to be risk factors for the development of occupational asthma.

Table 34–1. Selected Causes of Occupational Asthma in at-Risk Workers.

The pathogenesis of occupational asthma is complex and multifactorial, involving both environmental and host factors. The majority of patients with occupational asthma develop the disease within the first 1–2 years of exposure, although there are differences in the time to development of occupational asthma based on the molecular weight of the inciting antigen.

Occupational asthma can be classified as one of two types: immunological or nonimmunological (Table ...

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