The Rising Diagnosis of Occupational Asthma

The diagnosis of “occupational asthma” appears to be increasing in clinical medicine. Some of this may be due to occupational exposure, but the majority appears to be due to a relaxation in the criteria for the diagnosis of occupational asthma. The distinction is important since it has implications for Workers’ Compensation loss history and may impact the employability of the individual with asthma.

The relationship of clinical asthma and exposures in the workplace is usually difficult to conclusively establish. The diagnosis of occupational asthma requires a clinical diagnosis of asthma and establishment of work relatedness. The features include a compatible history, presence of airflow limitation and its reversibility, and demonstration of work relatedness by objective means. Objective work relatedness may be established by one or more of the following criteria:

1. Documented exposure to an agent known to give rise to occupational asthma
2. Work-related changes in FEV₁ or peak expiratory flow rates
3. Work-related changes in bronchial responsiveness
4. Positive response to specific inhalation challenge tests
5. Onset of asthma with a clear association with a symptomatic exposure to an irritant in the workplace (ACCP Consensus Statement)

Pulmonary Sensitizers
There are some substances in the workplace that are known to be pulmonary sensitizers, the exposure to which may result in clinical asthma. Examples of substances known to cause occupational asthma are western red cedar dust (plicatic acid is the active agent), proteolytic enzymes, isocyanates, and acid anhydrides. A few case reports have suggested that exposure to formaldehyde and formaldehyde resin dust may produce pulmonary sensitization and asthma-like symptoms; however, most investigators feel that there is insufficient evidence to link formaldehyde to immunologic-based asthma.

Diagnosis
A detailed past medical history is essential in establishing a diagnosis of occupational asthma. The history should be targeted to situations in which the pulmonary symptoms are initiated or aggrevated. Does the patient feel better during the weekends and holidays? What triggers attacks at home and work? What makes symptoms better or worse? What medications is the employee taking, when and with what effects? From a diagnostic perspective, it may be necessary to perform peak expiratory flow rates over a period of days or weeks to look for indications of reversible bronchoconstriction and their relationship to exposures or activities. Pulmonary function tests before and after exposures may be useful in making the diagnosis.

Occupational asthma is a diagnosis that will impact on the work status and employability of the individual. It should be made only when documented asthma attacks are demonstrated to be unequivocally related to exposures in the workplace to substances known to pulmonary sensitizers of asthmatogens.