Clinical Overview, Appendix A: Occupational Asthma
Occupational lung diseases which do not usually require chest imaging with ILO classification for surveillance or diagnosis.
One of the most common occupational lung diseases, occupational asthma (OA), is characterized by variable airflow obstruction, airway hyper-responsiveness and airway inflammation from workplace exposures. There are two main types: (1) OA occurring after a period of latency with on-going immunologic exposure, and (2) OA from non-immunologic exposures, often following a single exposure to a high concentration of a known irritant (e.g., chlorine or related compounds). Work-aggravated asthma is defined as pre-existing asthma that is exacerbated by workplace exposures such as secondhand smoke or extremes of temperature and humidity. Common immunologic exposures that can cause OA include low molecular weight chemicals (most commonly, isocyanates used in paints and foams, as well as wood dusts, acrylates and some metals such as platinum, nickel, cobalt and chromium) and high molecular weight (HMW) substances (e.g., latex, laboratory and farm animals, pharmaceutical agents, baking and detergent enzymes).
Typical symptoms of OA include cough, sputum production, wheezing, chest tightness and dyspnea. Pulmonary function testing to confirm the diagnosis of asthma may show airflow obstruction (FEV1/FVC ratio below the lower limit of normal) with significant improvement following bronchodilator (defined as a 12% or greater and >200 cc increase in FEV1). If airflow obstruction is not present on spirometry, methacholine challenge may be necessary to determine the presence and severity of bronchial hyper-responsiveness. Serial measurement of peak expiratory flow rates (PEFR) at and away from work is sometimes helpful. Skin prick testing or immunoassays for specific IgE using extracts of HMW substances may aid diagnosis in some circumstances. The chest radiograph in OA may be normal or show hyperinflation. HRCT is usually not necessary for the evaluation of suspected OA unless an abnormality is noted on chest radiograph, or if there is concern for other disease such as hypersensitivity pneumonitis.