Occupational Asthma

1. Occupational Asthma Tee L. Guidotti The George Washington University

2. Presentation of Occ Asthma • Immediate hypersensitivity reaction • Immediate bronchospasm • Isolated late response (usually sensitizer-induced) • Sleep disorder • Variable/dual response

3. Types of Occupational Asthma • New Onset - Sensitizer-induced - Irritant induced • Aggravation of underlying asthma • Reactive airways dysfunction syndrome (RADS) • Cold air- or exercise-induced syndrome • Airways reactivity secondary to hypersensitivity pneumonitis

4. Sensitizer-induced Specific antigen Minimal exposure Stereotyped response PPE often insufficient to control symptoms Medical removal usually necessary Irritant-induced Any irritant Moderate to heavy exposure Often variable PPE often effective in preventing episodes Medical removal the last resort Occupational Asthma

5. Sensitizer-Induced Occ Asthma • Sensitization to a specific antigen - low molecular-weight, “hapten” - high molecular weight • Reaginic Ab, mostly IgE, mediated • Presentation variable - late phase reactivity - immediate sensitivity - dual or variable responsiveness

6. Sensitizer-Induced Asthma 2 • Sensitization may occur at <OEL • Sensitizers may also be irritants (e.g. TDI,TMA) • Prior history of atopy does not predict risk of asthma! • Therefore no basis of exclusion of persons with allergies from workplace

7. Low MW Isocyanates Anhydrides Metal salts Epoxy resins Fluxes Persulfate Aldehydes High MW Pharmaceuticals Animal proteins Latex Cereals Seafood Proteolytic enzymes Wood constituents Common Sensitizers(Incomplete List!)

8. Irritant-Induced Occupational Asthma • More common, clinically, than sensitizer-induced • Often represents clinical expression of airways hyperactivity + irritant exposure • May be induced by any irritating exposure • Usually history of intolerance to second-hand tobacco smoke • Some irritant exposures may also be sensitizing: CHO, TDI,TMA • Classic example is “hot wire” asthma

9. RADS • Acute onset following exposure to irritant • Generally exposure of moderate severity • Prognosis good but may have several years of airway hyperactivity and sequelae • Often associated with: • upper airway problems • sleep disorder • Independent of prior history of airways reactivity • Conventional management

10. Aggravational Asthma • Very common • Existing airways reactivity: • asthma • hay fever and rhinitis • other airways disease (e.g. COPD) • Initial condition not occupational • Moderate irritant exposure • Provokes airways response • Usually self-limited

11. Patterns of Airways Response

12. Immediate response • Same shift, rapid onset • Reaginic antibody if sensitizer-induced • Acute mediators • Responds to conventional asthma Rx • Often difficult to distinguish from conventional asthma • Irritant-induced tends to be milder

13. Late Responders • Onset of bronchospasm hours after exposure • Usually wheezing post-shift • Often presents as a sleep disorder • If isolated, usually associated with certain antigens (Western red cedar, TDI) • Often combined

14. Dual/Variable effects • Dual responders may combine immediate + late responses • Variations may include cyclic bronchospasm (esp. Western red cedar) • May be prolonged, sustained response (TDI, byssinosis) • Usually slow recovery, relatively refractory to conventional Rx

15. Special Cases The following subsets of occupational asthma have special features: • Laboratory animal sensitivity (high risk of anaphylaxis) • Cotton dust, byssinosis • Grain dust • Hypersensitivity pneumonitis may have an airways component

16. Cold Air / Exercise-Induced Asthma • May be associated with: • dry cold air • exertion • hyperventilation • Work in cold, dry climates • Immediate response, short duration • Further exercise may improve airflow! • Mechanism: airway drying and cooling • stimulates vagal receptors • histamine, mediator release from mast cells

17. Principles of Evaluation • Demonstrate airways reactivity - History - Presence of wheezing • Spirometry • Methacholine challenge • Bronchoprovocation or substitute - Symptom diary - Pre/post shift

18. Methacholine Challenge • + Test confirms airways reactivity only • A functional test not specific for asthma - atopy - transient reactivity • Bronchoprovocation with with specific antigen preferable to diagnose sensitizer-induced asthma • -Tests can occur with quiescent occ asthma

19. Risks of Bronchoprovocation • Anaphylaxis • Iatrogenic reaction • Sensitization

20. Ancillary Tests • Clinical immunology - skin prick tests - RAST - ELISA • PEF or FEV1, symptom and medication diary • Pre/post shift and/or holiday PFTs • Work place HHE

21. Management • Conventional Rx for asthma • Medical removal – consider options • Physician’s First Report • Impairment Assessment (c.f. AMA guidelines) • Avoid irritants • Evaluate PPE

22. Compensation Management • Document causation • Document impairment (episodic?) • Medical removal required? • Claimant factors - degree of impairment - age - retraining Impairment – Disability

23. Pop Health Management • Treat as “Sentinel event” • Surveillance • Identification of specific hazard when possible • Hazard Control - engineering controls - PPE